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UC-NRLF 


MEMCAL    SCHOOL 


IN  MEMORIiUyi 
DR.    S.J.S.   ROGERS 


/ 


IBbik,. 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/elemephysioOOcarprich 


ELEMENTS    OF    PHYSIOLOGY. 


By  the  same  Author, 
PRINCIPLES 

OF 

GENERAL   AND    COMPARATIVE    PHYSIOLOGY 

WITH  NUMEROUS  ILLUSTRATIONS.    (AT  PRESS.) 

PRINCIPLES    OF    HUMAN    PHYSIOLOGY. 

WITH  NUMEROUS  ILLUSTRATIONS. 


A  POPULAR  TREATISE  ON  VEGETABLE  PHYSIOLOGY. 


WITH  NUMEROUS  CUTS. 


PUBLISHED  BY  LEA  AND  BLANCHARD. 


ELEMENTS 


OF 


PHYSIOLOGY, 


INCLUDING 


PHYSIOLOGICAL   ANATOMY, 


FOR  THE  USE  OF  THE  MEDICAL  STUDENT. 


BY 


WILLIAM  B./CARPENTER,  M.D.,F.R.S., 

rULLERIAN  PROFESSOR  OF  PHYSIOLOGY  IN  THE  ROYAL  INSTITUTION  OF  GREAT  BRITAIN  j 

MEMBER  OF  THE  AMERICAN  PHILOSOPHICAL  SOCIETY,  AND 

CORRESPONDING  MEMBER  OF  THE  NATIONAL  INSTITUTE  OF  THE  UNITED  STATES; 

ETC.  ETC. 


WITH  ONE  HUNDBED  AND  EIGHTY  ILLUSTBATIONS. 


PHILADELPHIA: 

LEA   AND    BLANCHARD. 

1846. 


PHILADELPHIA : 

T.  K.  AND  P.  G.  COLLINS, 

PRINTERS. 


AMERICAN  PUBLISHERS'  ADVERTISEMENT. 


The  sheets  of  this  volume,  in  their  passage  through  the  press, 
have  been  carefully  examined  by  Dr.  Meredith  Clymer,  the  Editor 
of  Dr.  Carpenter's  "Principles  of  Human  Physiology."  The  perfect 
adaptation  of  the  work  to  its  purposes  as  an  elementary  text-book, 
and  the  manner  in  which  it  is  brought  up  to  the  day,  have  rendered 
unnecessary  any  notes  or  additions ;  the  efforts  of  the  publishers, 
therefore,  have  been  directed  to  a  correct  reprint  of  the  London 
edition. 

That  it  may  correspond  in  size  with  the  Author's  other  works  on 
Physiology,  the  publishers  have  employed  a  type  larger  than  that 
used  in  the  London  edition,  and  consequently  they  have  been  induced 
to  substitute  the  word  '^Elements^^  in  place  of  ^^ Manual, ^^  which  was 
adopted  by  the  Author  more  with  reference  to  its  original  size  than 
to  its  contents,  as  stated  in  his  Preface. 

Philadelphia,  • 

April,  1846. 


il  ()•>{} 


PEEFACE. 


The  present  volume  owes  its  origin  to  a  desire,  on  the  part  of  the 
Publisher,  that  an  elementary  treatise  on  Physiology  should  be  added 
to  the  series  of  admirable  Students'  Manuals,  on  the  various  depart- 
ments of  Medical  Science,  which  he  has  already  issued.  But  for 
this  desire,  the  Author  would  have  preferred  not  again  to  present 
himself  so  soon  before  the  public,  in  a  capacity  in  which  he  fears 
that  he  has  already  trespassed  too  much  on  their  indulgence ;  his 
wish  being  rather  to  devote  as  much  time  as  possible  to  original 
inquiry  in  various  departments  of  Physiology,  which  stand  in  great 
need  of  elucidation. 

Although  this  Manual  combines,  in  some  degree,  the  scope  of  the 
Author's  two  larger  works  on  the  same  subject,  yet  it  cannot  be 
regarded  as  a  mere  abridgment  of  them ;  having  been  written  with 
very  little  reference  to  them,  and  on  a  plan  which  is  in  many  respects 
different.  His  object  has  been  to  convey  to  the  Student  as  clear  an 
idea  as  possible  of  the  principles  of  the  science,  to  point  out  the 
manner  in  which  these  principles  should  be  applied,  and  to  give  an 
outline  of  the  most  important  facts  which  indicate  the  nature  of  the 
various  changes  taking  place  in  the  living  organism.  In  following  out 
this  intention  he  has  thought  it  right  to  adopt  a  plan  which,  so  far  as  he 
knows,  is  a  novel  one : — namely,  to  commence  his  exposition  of  the 
characters  of  Organized  Structures  and  of  Vital  Phenomena  by  a  full 
account  of  the  Development  and  Metamorphoses  of  Cells,  and  of  the 
purposes  which  these  effect  in  the  living  body,  either  in  their  original 
or  in  their  altered  condition.  He  is  of  opinion  that  the  inferences, 
"which  may  be  drawn  from  the  observations  on  this  subject,  that  have 
rapidly  accumulated  during  the  last  few  years,  are  entitled  to  hold 
the  same  rank  in  Physiological  Science  as  that  taken  by  the  doctrine 
of  Mutual  Attraction  in  General  Physics,  or  of  Elective  Affinity  in 
Chemistry ;  and  that  the  enunciation  and  development  of  these  should 


viii  PREFACE. 

consequently  hold  the  first  place  in  an  Elementary  Treatise  on  Physi- 
ology. The  third  chapter,  constituting  more  than  one-fourth  of  the 
entire  Treatise,  is  therefore  devoted  to  this  subject.  The  topics  em- 
braced in  the  first  two  chapters,  and  in  the  whole  of  the  Second 
Book,  are  treated  of  on  a  much  more  extended  scale  in  the  Author's 
"Principles  of  General  and  Comparative  Physiology,"  and  *' Prin- 
ciples of  Human  Physiology,"  to  which  he  would  refer  those  who 
desire  further  information  upon  them.  As  the  matter  of  which  those 
volumes  are  composed  is  itself  condensed  to  the  utmost  possible  de- 
gree, it  is  manifestly  impossible  that  the  present  Manual  should  con- 
tain more  than  a  mere  outline  of  the  subjects  of  which  they  treat. 
The  Author  has  endeavoured  to  select  what  is  of  the  most  import- 
ance to  the  Student,  and  lies  most  readily  within  his  comprehension ; 
and  has  rather  desired  to  impress  the  minds  of  his  readers  with  a 
clear  notion  of  what  he  considers  the  leading  or  typical  facts  of  the 
science,  than  to  load  his  memory  with  details. 

The  Author  may  be  permitted  to  direct  attention  to  the  copiousness 
and  beauty  of  the  illustrations,  which  the  liberality  of  the  Publisher 
has  allowed  him  to  introduce.  The  greater  part  of  the  wood-engrav- 
ings have  been  executed,  expressly  for  this  volume,  by  Mr.  Vasey, 
whose  skill  and  fidelity  have  recently  shown  themselves  to  be  as 
great  in  the  treatment  of  anatomical  subjects  as  they  have  been  long 
known  to  be  in  the  representation  of  objects  of  natural  history. 

Stoke  Newington, 
Feb.  20th,  1846. 


TABLE   OF   CONTENTS 


BOOK  I. 

GENERAL  PHYSIOLOGY. 

Chapter  Page 

I.  Ox  THE  Nature  and  Objects  of  the  Science  of  Phtsiologt     -  -  17 

1.  Of  Organic  Structures        -            -           -           -           -  -  18 

2.  Of  Vital  Actions      -------  25 

3.  Connection  between  Vitality  and  Organization      -           -  -  48 

II.  Of  the  Vital  Stimuli      -------58 

1.  Of  Light,  as  a  Condition  of  Vital  Action                -            -  -  61 

2.  Of  Heat,  as  a  Condition  of  Vital  Action     -            -            -  -  72 

3.  Of  Electricity,  as  a  Condition  of  Vital  Action        -            -  -  98 

4.  Of  Moisture,  as  a  Condition  of  Vital  Action          -           -  -  loi 

III.  Of  the  Elementary  Parts  of  Animal  Structures       -            -  -  109 

1.  Of  the  original  Components  of  the  Animal  Fabric            -  -  IH 

2.  Of  the  Simple  Fibrous  Tissues       -            -            -            -  -  123 

3.  Of  the  Basement  or  Primary  Membrane    -            -            -  -  133 

4.  Of  Simple  Isolated  Cells,  employed  in  the  Organic  Functions  -  136 
6.  Of  Cells  connected  together,  as  permanent  constituents  of  the 

Tissues     -            --            -            -            -            -  -  159 

6.  Of  Cells  coalesced  into  Tubes,  with  Secondary  Deposit    -  -  203 


BOOK  II. 

SPECIAL  PHYSIOLOGY. 

IV.  Of  Food,  and  the  Digestive  Process       -----  243 

1.  Sources  of  the  Demand  for  Aliment            -            -            -            -  243 

2.  Of  the  Digestive  Apparatus,  and  its  Actions  in  general     -            -  261 

3.  Of  the  Movements  of  the  Alimentary  Canal          -            -            -  266 

4.  Of  the  Secretions  poured  into  the  Alimentary  Canal,  and  of  the 

Changes  which  they  effect  in  its  contents            -            .            .  273 

5.  Of  Hunger,  Satiety,  and  Thirst       -           -           -           -           -  282 

V.  Of  Absorption  and  Sanguification        -----  285 

1.  Of  Absorption  from  the  Digestive  Cavity               -            .            .  285 

2.  Of  the  Passage  of  Chyle  along  the  Lacteals,  and  its  admixture 

with  the  Lymph  collected  from  the  General  System        -            -  289 

3.  Of  the  Spleen,  and  other  Glandular  appendages  to  the  Lymphatic 

System      ...-----  294 

4.  Of  the  Composition  and  Properties  of  the  Chyle  and  Lymph        -  299 

5.  Of  Absorption  from  the  External  and  Pulmonary  Surfaces           -  303 

6.  Of  the  Composition  and  Properties  of  the  Blood  -           -           -  304 


Page 

•        • 

• 

312 

t  Fluid 

. 

312 

. 

. 

314 

. 

. 

329 

. 

. 

337 

. 

m 

340 

- 

- 

349 

. 

. 

353 

. 

. 

353 

. 

. 

355 

. 

. 

361 

. 

. 

362 

X  TABLE  OF  CONTENTS. 

Chaptek 
VI.  Of  the  CiHCULATio^r  of  the  Blood 

1.  Nature  and  Objects  of  the  Circulation  of  Nutrient  Fluid 

2.  Different  forms  of  the  Circulating  Apparatus 

3.  Action  of  the  Heart 

4.  Movement  of  the  Blood  in  the  Arteries 

5.  Movement  of  the  Blood  in  the  Capillaries 

6.  Movement  of  Blood  in  the  Veins    - 

VII.  Of  Nutritiok       --.-_. 

1.  Selecting  Power  of  Individual  Parts 

2.  Varying  Activity  of  tne  Nutritive  Processes 

3.  Of  Death,  or  Cessation  of  Nutrition 

4.  Disordered  Conditions  of  the  Nutritive  Processes 

Vni.  Of  Respiration    -            -            -            -            -            -            -            -  367 

1.  Essential  Nature  and  Conditions  of  the  Respiratory  Process        -  367 

2.  Different  forms  of  the  Respiratory  Apparatus  in  the  lower  Animals  373 

3.  Mechanism  of  Respiration  in  Mammalia  and  in  Man        -            -  385 

4.  Chemical  Phenomena  of  Respiration         -            -            -            -  392 

5.  Effects  of  Insufficiency,  or  Suspension,  of  the  Aerating  Process  -  399 

IX.  Of  Secretiox        ---.---.  403 

1.  Of  the  Secreting  Process  in  general;  and  of  the  Instruments  by 

which  it  is  effected            -..-.-  403 

2.  Of  the  Liver,  and  the  Biliary  Excretion      -            -            .            -  410 

3.  Of  the  Kidneys,  and  the  Urinary  Excretion            -            -            -  416 

4.  Of  the  Cutaneous  and  Intestinal  Glandulae             -            -            -  425 

5.  General  Summary  of  the  Excreting  Processes       -            -            -  430 

X.  Of  the  DETELOPMEiirT  OF  Light,  Heat,  and  Electricitt  in  the  Animal 

BoDr          ........  434 

^I.  Of  Reproduction               -.-.---  443 

1.  General  View  of  the  Nature  of  the  Process           ...  443 

2.  Action  of  the  Male  ..-----  446 

3.  Action  of  the  Female          ..---.  449 

XII.  Of  the  Nervous  System               -._.--  476 

1.  General  view  of  the  operations,  of  which  the  Nervous  System  is 

the  Instrument      --.--.-  476 

2.  Comparative  Structure  and  Actions  of  the  Nervous  System          -  481 

3.  Functions  of  the  Spinal  Cord  and  its  Nerves         ...  498 

4.  Functions  of  the  Medulla  Oblongata           ....  507 

5.  Functions  of  the  Sensory  Ganglia               ....  510 

6.  Functions  of  the  Cerebellum           -----  518 

7.  Functions  of  the  Cerebrum             .            .            -            -            -  520 

8.  Functions  of  the  Sympathetic  System        -            -            -            -  526 

XIII.  Of  Sensation,  General  and  Special       -----  528 

1.  Of  Sensation  in  general       ------  528 

2.  Of  the  Sense  of  Touch        ------  533 

3.  Of  the  Sense  of  Taste         .-.---  535 

4.  Of  the  Sense  of  Smell         ..----  537 

5.  Of  the  Sense  of  Hearing    - 539 

6.  Of  the  Sense  of  Sight         ------  542 

XIV.  Of  the  Voice,  and  Speech            ------  552 


LIST  OF  WOOD  ENGRAVINGS. 


Fig.  Page 

1.  Simple  isolated  Cells,  containing  reproductive  molecules             -           -  33 

2.  Fibrous  structure  of  exudation-membrane             .            .            -            >  120 

3.  Fibrous  membrane  lining  egg-shell  (original)       -            -            -            -  120 

4.  White  fibrous  tissue  of  areolar  tissue  and  tendon             -            -            .  124 

5.  White  fibrous  tissue  of  ligament                _            _            -            _            _  125 

6.  Yellow  fibrous  tissue  of  ligamentum  nuchae         -            -            -            -  125 

7.  Capillary  vessels  of  Skin;  after  Berres    -            -            -            -            -  132 

8.  Capillary  vessels  of  Intestinal  villi;  after  Berres              ...  132 

9.  Capillary  vessels  around  orifices  of  Mucous  follicles;  after  Berres         -  132 

10.  Capillary  vessels  around  follicles  of  Parotid  Gland;  after  Berres            -  132 

11.  Distribution  of  Sensory  nerves  in  Skin;  after  Gerber       -            -         '   -  133 

12.  Primary  membrane,  with  germinal  spots ;  after  Goodsir               -            -  134 

13.  Primary  membrane,  showing  component  cells ;  after  Goodsir      -            -  135 

14.  Simple  isolated  cells,  containing  reproductive  molecules              -            -  137 

15.  Cells  from  fluid  of  Herpes;  after  Addison             ...            -  133 

16.  Oblique  section  of  Epidermis;  after  Henle            -            -            -            -  145 

17.  Epidermic  cells  from  Conjunctiva;  after  Gerber              -            -            -  145 

18.  Portion  of  Choroid-coat,  showing  pigment  cells;  after  Gerber     -            -  147 

19.  Separate  Pigment-cells       -------  147 

20.  Detached  epithelium-cells  from  mucous  membrane  of  mouth      -            -  149 

21.  Pavement-epithelium  from  bronchial  tubes;  after  Lebert              -            -  149 

22.  Layer  of  cylindrical  epithelium,  with  cilia;  after  Henle               -            -  150 

23.  Follicles  from  liver  of  Crab,  with  contained  secreting  cells;  after  Goodsir  153 

24.  Follicles  of  Mammary  gland,  with  contained  secreting  cells ;  after  Lebert  153 

25.  Secreting  Cells  of  Human  Liver   ------  154 

26.  Formation  of  Spermatozoa  within  cells;  after  Wagner                -            -  154 

27.  Diagram  of  Intestinal  Mucous  membrane,  during  digestion  and  absorption 

of  chyle;  after  Goodsir               ------  156 

28.  Diagram  of  Intestinal  Mucous  membrane,  in  intervals  of  digestion;  after 

Goodsir                --------  156 

29.  Extremity  of  Placental  villus ;  after  Goodsir         -            -            -            -  157 

30.  Parent-cells,  with  contained  secondary  cells,  of  cancerous  structure ;  after 

Lebert     ---------  160 

31.  Progressive  stages  of  cell-growth,  in  shell-membrane  (original)              -  162 

32.  Progressive  stages  of  coalescence  of  cells,  in  shell-membrane  (original)  162 

33.  Transition  from  cellular  to  fusiform  tissue;  after  Lebert              -            -  164 

34.  Fusiform  tissue  of  plastic  exudations  ;  after  Lebert          -            -            -  164 

35.  Areolar  and  Adipose  tissue;  after  Berres               -            -            -            .  164 

36.  Capillary  network  around  Fat-cells;  after  Berres             -            -            -  165 

37.  Section  of  Cartilage;  after  Schwann         -----  168 

38.  Distribution  of  vessels  on  surface  of  Cartilage;  after  Toynbee    -            -  170 

39.  Nutrient  vessels  of  Cornea;  after  Toynbee           -            -            -            -  171 

40.  Cancellated  structure  at  extremity  of  Femur         -            -            -            -  173 

41.  Lacunae  of  Osseous  substance       ------  174 

42.  Section  of  Bony  Scale  of  Lepidosteus  (original)               -            -            -  174 

43.  Network  of  Haversian  canals,  from  vertical  section  of  Tibia      -           -  176 

44.  Transverse  section  of  long  bone               -           -           -           -           -  177 


Xll 


LIST  OF  WOOD  ENGRAVINGS. 


Fig. 
45. 
46. 
47. 
48. 
49. 
60. 
51. 
52. 
53. 
54. 
55. 
56. 
57. 
58. 
59. 
60. 
61. 
62. 
63. 
64. 
65. 
66. 
67. 
68. 
69. 
70. 
71. 

72. 

73. 

74. 

75. 

76. 

77. 

78. 

79. 

80. 

81. 

82. 

83. 

84. 

85. 

86. 

87. 

88. 

89. 

90. 

91. 

92. 

93. 

94. 

95. 

96. 

97. 

98. 

99. 
100. 
101. 
102. 
103. 
104. 
105. 


.  Shell  of  Echinus  (original)  -  -  -  . 

,  Sections  of  Shell  of  Pinna  (original) 
Tubular  shell-structure  from  Anomia  (original) 
Section  of  Cartilage,  near  seat  of  Ossification    - 
Section  of  Cartilage,  at  the  seat  of  Ossification  - 
Vessels  of  Dental  Papilla;  after  Berres 
Oblique  section  of  Dentine;  after  Owen 
Vertical  section  of  Human  Molar  Tooth;  after  Nasmyth 
Development  of  Teeth ;  after  Goodsir 
Fasciculus  of  Striated  Muscular  fibre ;  after  Mandll 
Non-striated  Muscular  fibres;  after  Bowman 
Ultimate  fibriilae  of  striated  fibre  (original) 
Muscular  fibre  cleaving  into  disks;  after  Bowman 
Transverse  section  of  muscular  fibres;  after  Bowman 
Structure  of  ultimate  fibriilae  of  striated  fibre  (original) 
Nucleated  fibres  from  non-striated  muscle ;  after  Bowman 
Nuclei  in  striated  muscular  fibres  of  foetus;  after  Bowman 
Capillaries  of  Muscle ;  after  Berres 
Distribution  of  nerves  in  Muscle;  after  Burdach 
Capillaries  of  Nervous  centres ;  after  Berres 
Components  of  gray  substance  of  Brain;  after  Purkinje 
Structure  of  Ganglion  of  Sympathetic;  after  Valentin   - 
Distribution  of  Sensory  Nerves  in  lip;  after  Gerber 
Capillaries  at  margin  of  lips;  after  Berres 
Diagram  of  Nervous  System  (original)  -  -  - 

Section  of  Human  Stomach         .  .  -  . 

Mucous  coat  of  small  intestine,  showing  Villi,  and  orifices  of  follicles ; 
after  Boehm        ...... 

Stomach  of  Sheep  -  -  .  .  . 

Section  of  Stomach  of  Sheep,  showing  demi-canal ;  after  Flourens 

Lobule  of  Parotid  Gland  -  -  .  .  - 

Gastric  glandulae;  after  Wagner  .  -  . 

Orifices  of  gastric  tubuli;  after  Boyd       - 

Distribution  of  Capillaries  in  Intestinal  Villi;  after  Berres 

Commencement  of  lacteal,  in  intestinal  villus;  after  Krause 

Diagram  of  Lymphatic  gland;  after  Goodsir 

Epithelial  cells  of  intra-glandular  lymphatic;  after  Goodsir 

Course  of  Thoracic  duct  .  _  .  - 

Appearance  of  inflamed  Blood;  after  Addison    - 

Vascular  area  of  Fowl's  egg;  after  Wagner 

Diagram  of  the  Circulation  in  Fish         .  -  - 

Diagram  of  the  Circulation  in  Reptile     .  -  - 

Diagram  of  complete  Double  Circulation 

Anatomy  of  Human  Heart  and  Lungs    -  .  - 

Capillaries  of  Muscle ;  after  Berres        -  -  - 

Capillaries  of  Nervous  centres;  after  Berres 

Capillaries  of  Glandular  follicles;  after  Berres 

Capillaries  of  Conjunctival  membrane  ;  after  Berres 

Capillaries  of  Choroid  coat;  after  Berres 

Capillaries  around  orifices  of  mucous  follicles;  after  Berres 

Capillaries  in  Skin  of  finger;  after  Berres 

Capillaries  in  fungiform  papilla  of  Tongue ;  after  Berres 

Doris,  showing  branchial  tufts;  after  Alder  and  Hancock 

One  of  the  arborescent  processes  of  gills  of  Doris;  ditto 

Respiratory  apparatus  of  Insects 

Diagram  of  different  forms  of  Respiratory  Apparatus  (original) 

Capillaries  of  Gill  of  Eel  (original)         _  -  - 

Section  of  Lung  of  Turtle;  after  Boganus  -  r 

Capillaries  of  Human  Lung  (original)     -  -  - 

Simple  glandular  follicles;  after  Miiller 

Embryonic  development  of  Liver;  after  Miiller 

Rudimentary  Pancreas,  from  Cod;  after  Miiller 


Pass 
181 
183 
184 
187 
187 
192 
193 
196 
198 
204 
204 
205 
205 
205 
206 
207 
208 
208 
209 
226 
226 
227 
228 
228 
236 
263 

264 
269 
270 
273 
275 
275 
287 
288 
289 
289 
290 
311 
319 


327 
328 
341 
342 
342 
342 
342 
342 
342 
343 
372 
375 
377 
378 
379 
382 
386 
407 
407 
407 


LIST  OF  WOOD  ENGRAVINGS.  xiii 

Fio.  Page 

106.  Mammary  Gland  of  Ornethorhyncees ;  after  Miiller       -            -            -  407 

107.  Meibomian  Glands;  after  Miiller              -            -            .            .            .  408 

108.  Portion  of  Co wper's  Gland;  after  Miiller             -            -            -            .  4O8 

109.  Lobule  of  Lachrymal  Gland;  after  Miiller           -            -      '       -            -  408 

110.  Hepatic  Follicles  from  Crab;  after  Goodsir         -            -            -            -  409 

111.  Ultimate  Follicles  from  Mammary  gland;  after  Lebert               -            -  409 

112.  Surface  of  Lobule  of  Liver  of  Squilla;  after  Miiller       -            -            -  410 

113.  Interior  of  Lobule  of  Liver  of  Squilla;  after  Miiller       -            -            -  410 

114.  Liver  of  Tadpole;  after  Miiller                -            -            -            -            -  411 

115.  Distribution  of  Blood-vessels  in  Lobules  of  Liver;  after  Kiernan          -  412 

116.  Connections  of  Lobules  of  Liver  with  Hepatic  vein;  after  Kiernan      -  412 

117.  Distribution  of  Hepatic  ducts  around  Lobules  of  Liver;  after  Kiernan  413 

118.  Secreting  Cells  of  Liver                ......  413 

119.  Development  of  Kidney,  in  embryo  of  Lizard;  after  Miiller      -            -  416 

120.  Kidney  of  foetal  Boa;  after  Muller           .....  417 

121.  Portion  of  Kidney  of  Coluber;  after  Miiller        ...            -  417 

122.  Fasciculus  of  tubuli  uriniferi  of  Bird;  after  Muller        .            .            -  417 

123.  Section  of  Kidney             .......  4I8 

124.  Section  of  portions  of  Kidney,  slightly  magnified;  after  Wagner            -  418 

125.  Distribution  of  vessels  in  Kidney  ;  after  Bowman            ...  418 

126.  Vertical  section  of  Skin    -            -            -            -            -            -            -  425 

127.  Hepatic  Cells  gorged  with  Fat;  after  Bowman   -            -            -            -  432 

128.  Simple  isolated  cells,  with  reproductive  molecules          -            -            -  443 

129.  Formation  of  Spermatozoa  within  seminal  cells;  after  Wagner              -  446 

130.  Anatomy  of  the  Testis      .......  447 

131.  Plan  of  early  Uterine  Ovum  ;  after  Wagner        ....  457 

132.  Vascular  Area  of  Fowl's  Egg ;  after  Wagner     ....  460 

133.  Diagram  of  Ovum,  at  commencement  of  separation  of  digestive  cavity; 

after  Wagner     ........  462 

134.  Diagram  of  Ovum,  showing  the  formation  of  the  Amnion  ;  after  Wagner  462 

135.  Diagram  of  Human  Ovum,  in  second  month,  showing  the  Allantois;  after 

Wagner             ........  463 

136.  Extremity  of  Placental  Villus;  after  Goodsir       ....  464 

137.  External  membrane  and  cells  of  placental  villus  ;  after  Goodsir             .  464 

138.  Diagram  illustrating  the  arrangement  of  the  placental  decidua ;   after 

Goodsir              ..-...-.  465 

139.  Plan  of  the  FoBtal  Circulation      ......  466 

140.  Termination  of  portion  of  milk-duct  in  follicles  ;  after  Sir  A.  Cooper    -  470 

141.  Portion  of  the  Ganglionic  tract  of  Polydesmus;  after  Newport    -            -  488 

142.  Human  embryo  at  sixth  week ;  after  Wagner     -            -            -            -  496 

143.  Diagram  of  the  origin  and  termination  of  Spinal  and  Cerebral  nerve      -  502 

144.  Section  of  the  base  of  the  Brain              .....  512 

145.  Mesial  surface  of  longitudinal  section  of  Brain    ....  522 

146.  Capillary  network  at  margin  of  Lips;  after  Berres         ...  533 

147.  Distribution  of  tactile  nerves  in  Skin  ;  after  Gerber         ...  534 

148.  Capillaries  of  fungiform  papilla  of  Tongue;  after  Berres       .     -            -  536 

149.  Distribution  of  Olfactory  nerve      ......  637 

150.  Refraction  of  rays  of  light  through  convex  lens  ....  ,543 

151.  Formation  of  images  in  eye          ......  544 

152.  Capillary  network  of  Retina;  after  Berres            -            -            -            -  546 

153.  Structure  of  the  Larynx;  after  Willis       .....  553 

Two  plates  embracing  27  figures,  making  altogether  180  figures. 


EXPLANATION  OF  PLATE  L 


The  Figures  in  this  Plate  represent  the  Cells  floating  in  the  various  animal  fluids ; 
and  they  are  all,  with  the  exception  of  Figs.  4  and  5,  copied  from  the  representations 
given  by  M.  Donne  in  his  Atlas  de  I'Anatomie  Microscopique.  These  representations 
are  transcripts  of  Daguerreotype  pictures,  obtained  from  the  objects,  by  a  solar  micro- 
scope, with  a  magnifying  power  of  400  diameters. 

Fig.  1.  Red  Corpuscles  of  Human  Blood,  viewed  by  their  flattened  surfaces  (§  215). 

Fig.  2.  Red  Corpuscles  of  Human  Blood,  adherent  by  their  flattened  surfaces,  so  as 
to  form  rolls  ; — at  a,  the  entire  surfaces  are  adherent;  at  6,  their  surfaces 
adhere  only  in  part. 

Fig.  3.  Red  Corpuscles  of  Human  Blood,  exhibiting  the  granulated  appearance  which 
they  frequently  present,  a  short  time  after  being  withdrawn  from  the  vessels. 

Fig.  4.  Colourless  Corpuscles  of  Human  Blood  (§  212). 

Fig.  5.  The  same,  enlarged  by  the  imbibition  of  water. 

Fig.  6.  Red  Corpuscles  of  Frog's  Blood  (§  215). 

Fig.  7.  The  same,  treated  with  dilute  acetic  acid ;  the  first  effect  of  which  is  to  render 
the  nucleus  more  distinct,  as  at  b ;  after  which  the  outer  vesicle  becomes 
more  transparent,  and  its  solution  commences,  as  at  a. 

Fig.  8.  The  same,  treated  with  water ;  at  a  is  seen  a  corpuscle  nearly  unaltered,  ex- 
cept in  having  the  nucleus  more  sharply  defined ;  at  b,  others  which  have 
become  more  spherical,  under  the  more  prolonged  action  of  water;  ate, 
the  nucleus  is  quitting  the  centre,  and  approaching  the  circumference  of 
the  disk ;  at  c?  it  is  almost  freeing  itself  from  the  envelop  ;  and  at  e  it  has 
completely  escaped. 

Fig.    9.  Globules  of  Mucus,  newly  secreted  (§  237). 

Fig.  10.  The  same,  acted  on  by  acetic  acid. 

Fig.  11.  Globules  of  Pus,  from  a  phlegmonous  abscess  (§  632). 

Fig.  12.  The  same,  acted  on  by  acetic  acid. 


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EXPLANATION  OF  PLATE  IL 


The  Figures  in  this  Plate  represent  the  principal  forms  of  the  Nervous  Centres  in 
different  classes  of  animals.  The  1st  is  copied  from  a  recent  Memoir  by  M.  Blanch- 
ard;  the  2d,  3d,  and  4th,  from  Mr.  Newport's  delineations;  the  5th  to  the  13th  from 
the  interesting  work  of  M.  Guillot  on  the  Comparative  Anatomy  of  the  Encephalon 
in  the  different  classes  of  Vertebrata;  and  the  two  last  from  the  work  of  M.  Leuret 
on  the  same  subject. 

Fig.  1.  Nervous  System  of  Solen;  a,  a,  cephalic  ganglia,  connected  together  by  a 
transverse  band  passing  over  the  (Esophagus,  and  connected  with  the  other 
ganglia  by  cords  of  communication ;  b,  pedal  ganglion,  the  branches  of 
which  are  distributed  to  the  powerful  muscular  foot;  c,  branchial  ganglion, 
the  branches  of  which  proceed  to  the  gills  d,  d,  the  siphons  c,  e,  and  other 
parts.  On  some  of  these  branches,  minute  ganglia  are  seen ;  as  also  at 
/,/,  on  the  trunks  that  pass  forwards  from  the  cephalic  ganglia  (§  852). 

Fig.  2.  Nervous  System  of  the  Larva  of  Sphinx  ligustri,-  a,  cephalic  ganglia;  1 — 12, 
ganglia  of  the  ventral  cord  (§  856). 

Fig.  3.  Thoracic  portion  of  the  Nervous  System  of  the  Pupa  of  Sphinx  ligustri;  a, 
b,  c,  three  ganglia  of  the  ventral  cord ;  d,  d,  their  connecting  trunks;  e,  e, 
respiratory  ganglia  (§  862). 

Fig.  4.  Anterior  portion  of  the  Nervous  System  of  the  Imago  of  Sphinx  ligustri;  a, 
cephalic  ganglia ;  b,  b,  eyes ;  c,  anterior  median  ganglion,  and  d,  d,  poste- 
rior lateral  ganglia  of  stomato-gastric  system;  e,f,  large  ganglionic  masses 
in  the  thorax,  giving  origin  to  the  nerves  of  the  legs  and  wings  (§  863). 

Fig.  5.  Brain  of  the  Perchy  seen  from  above  (§  869.) 

Fig.  6.  The  same,  as  seen  from  below. 

Fig.  7.  Interior  of  the  same,  as  displayed  by  a  vertical  section. 

The  following  references  are  common  to  the  three  preceding,  and  to  the  succeed- 
ing figures. 

a,  a.  Olfactory  lobes  or  ganglia. 

b,  by  Cerebral  ganglia  or  Hemispheres. 

c,  c.  Optic  lobes. 

d,  Cerebellum. 

e,  Spinal  Cord. 
/,  Pineal  gland. 

f,  Lobi  inferiores  (their  precise  character  not  determined). 
,  Pituitary  body. 
i,  Optic  Nerves. 
Fig.    8.  Brain  of  the  Common  Lizard,  seen  from  above  (§  871). 
Fig.    9.  The  same,  as  seen  from  below. 
Fig.  10.  The  same,  as  displayed  by  a  vertical  section. 
Fig.  11.  Brain  of  the  Common  Goose,  seen  from  above  (§  872). 
Fig.  12.  The  same,  as  seen  from  below. 
Fig.  13.  The  same,  as  displayed  by  a  vertical  section. 
Fig.  14.  Brain  of  the  Sheep,  viewed  sideways  (§  873). 
Fig.  15.  The  same,  as  displayed  by  a  vertical  section. 

In  addition  to  the  parts  indicated  by  the  preceding  references,  we  have  here  to 
notice;— A;,  the  corpus  callosum;  /,  the  septum  lucidum,  and  m,  the  Pons  Varolii. 


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BOOK   I. 

GENERAL   PHYSIOLOGY, 


CHAPTER  I. 

'     ON  THE  NATURE  AND  OBJECTS  OF  THE  SCIENCE  OF  PHYSIOLOGY. 

1.  The  general  distribution  of  the  objects  presented  to  us  by  ex- 
ternal Nature,  into  three  kingdoms, — the  animal,  the  vegetable,  and 
the  mineral, — is  familiar  to  every  one ;  and  not  less  familiar  is  the 
general  distinction  between  living  bodies,  and  dead  inert  matter. 
True  it  is,  that  we  cannot  always  clearly  assign  the  limits,  which  sepa- 
rate these  distinct  classes  of  objects.  Even  the  professed  naturalist 
is  constantly  subject  to  perplexity,  as  to  the  exact  boundary  between 
the  animal  and  the  vegetable  kingdoms;  and  the  distinction  between 
animal  and  vegetable  structures,  on  the  one  hand,  and  mineral  masses 
on  the  other, — or  between  living  bodies,  and  aggregations  of  inert  mat- 
ter,— is  by  no  means  so  obvious  in  every  case,  as  to  be  at  once  per- 
ceptible to  the  unscientific  observer.  Thus,  a  mass  of  Coral,  if  its 
growing  portion  be  kept  out  of  view^,  or  a  solid  Nullipore  attached  to 
the  surface  of  a  rock,  might  be  easily  confounded  with  the  mineral 
bodies  to  which  they  bear  so  close  a  resemblance;  and  a  minute  ex- 
amination might  be  required  to  detect  the  difference.  Nevertheless, 
a  well-marked  distinction  does  exist  between  the  organized  structures 
of  plants  and  animals,  and  the  inorganic  aggregations  of  Mineral 
matter ;  as  well  as  between  the  condition  of  a  living  being,  whether 
Animal  or  Plant,  and  that  of  dead  or  inert  Mineral  bodies.  It  is  upon 
these  distinctions,  which  are  usually  obvious  enough,  that  the  sciences 
of  Anatomy  and  Physiology  are  founded  ;  these  sciences  taking 
cognizance, — the  former  of  those  structures  which  are  termed  organ- 
ized^— and  the  latter  of  the  actions  which  are  peculiar  to  those  struc- 
tures, and  which  are  distinguished  by  the  term  vital.  It  will  be 
desirable  to  consider,  in  a  somewhat  systematic  order,  the  principal 
ideas  which  we  attach  to  these  terras ;  as  we  shall  be  thus  led  most 
directly  to  the  distinct  comprehension  of  the  nature  and  object  of 
Physiological  science. 
2 


18  NATURE  AND  OBJECTS  OF  THE 


1.  Of  Organic  Structures. 

2.  Organized  structures  are  characterized,  in  the  first  place,  by  the 
peculiarities  of  their  form.  Wherever  a  definite  form  is  exhibited  by 
Mineral  substances,  it  is  bounded  by  straight  lines  and  angles,  and  is 
the  effect  of  the  process  termed  crystalization.  This  process  results 
from  the  tendency  which  evidently  exists  in  particles  of  matter,  espe- 
cially when  passing  gradually  from  the  fluid  to  the  solid  state,  to 
arrange  themselves  in  a  regular  and  conformable  manner  in  regard  to 
one  another.  There  is,  perhaps,  no  inorganic  element  or  combination, 
which  is  not  capable  of  assuming  such  a  form,  if  placed  in  circum- 
stances adapted  to  the  manifestation  of  this  tendency  among  its  parti- 
cles; but  if  these  circumstances  should  be  wanting,  and  the  simple 
cohesive  attraction  is  exercised  in  bringing  them  together,  without 
any  general  control  over  their  direction,  an  indefinite  or  shapeless  figure 
is  the  result.  Neither  of  these  conditions  finds  a  parallel  in  the 
Organized  creation.  From  the  highest  to  the  lowest  we  find  the 
shape  presenting  a  determinate  character  for  each  species  or  race^ 
with  a  certain  limited  amount  of  variation  amongst  individuals  ;  and 
this  shape  is  such,  that,  instead  of  being  circumscribed  within  plane 
surfaces,  straight  lines,  and  angles,  organized  bodies  are  bounded  by 
convex  surfaces,  and  present  rounded  outlines.  We  may  usually 
gather,  moreover,  from  their  external  form,  that  they  are  composed 
of  a  number  of  dissimilar  parts,  or  organs  ;  which  are  combined  to- 
gether in  the  one  individual  body,  and  are  characteristic  of  it.  Thus, 
in  the  Vertebrated  or  Articulated  animal  we  at  once  distinguish  the 
head  and  extremities  from  the  trunk,  which  constitutes  the  principal 
mass  ;  and  where  there  exist  no  external  organs  of  such  distinctness, 
as  in  some  Mollusks,  the  rounded  character  of  the  general  form  is 
sufficiently  characteristic.  The  very  simplest  grades  of  animal  and 
vegetable  life  present  themselves  under  a  form,  which  approaches 
more  or  less  closely  to  the  globular.  It  is  among  the  lower  tribes  of 
both  kingdoms,  that  we  find  the  greatest  tendency  to  irregular  de- 
partures from  the  typical  form  of  the  species ;  and  thus  is  presented 
an  approach,  on  the  one  hand,  to  that  indefiniteness  which  is  charac- 
teristic of  uncrystaline  mineral  masses  ;  and,  on  the  other,  to  that 
variety  of  crystaline  forms  which  the  same  mineral  body  may  pre- 
sent, according  to  the  circumstances  which  influence  its  crystaliza- 
tion. 

3.  With  regard  to  size,  again,  nearly  the  same  remarks  apply.  The 
magnitude  of  Inorganic  masses  is  entirely  indeterminate,  being  alto- 
gether dependent  upon  the  number  of  particles  which  can  be  brought 
together  to  constitute  them.  On  the  other  hand,  the  size  of  Organized 
structures  is  restrained,  like  their  form,  within  tolerably  definite  limits, 
which  may  nevertheless  vary  to  a  certain  extent  among  the  indi- 
viduals of  the  same  species.  These  limits  are  least  obvious  in 
vegetables,  and  in  the  lower  classes  of  animals.     A  forest  tree  may 


SCIENCE  OF  PHYSIOLOGY.  'f9 

go  on  extending  itself  to  an  almost  indefinite  extent ;  certain  species 
of  sea-weed  attain  a  length  of  many  hundred  feet,  and  their  growth 
does  not  appear  to  undergo  any  check;  and  the  same  may  he  said  of 
those  enormous  masses  of  coral,  which  compose  so  many  islands  and 
reefs  in  the  Polynesian  Archipelago,  or  of  which  the  debris  seem  to 
have  constituted  many  of  the  calcareous  rocks  of  ancient  formation. 
But  in  these  cases  the  increase  is  produced,  not  so  much  by  the  con- 
tinued development  of  the  individual,  as  by  the  continued  production 
of  new  individuals,  which  remain  in  connection  with  the  original. 
Thus  each  bud  of  a  tree  may  be  regarded  as  a  distinct  individual  ; 
because,  if  placed  under  favourable  circumstances,  it  can  maintain 
its  life  by  itself,  and  can  perform  all  the  actions  proper  to  the  species; 
and,  consequently,  the  indefinite  extension  of  the  tree  by  the  multi- 
plication of  buds  is  not  in  reality  that  exception  to  the  rule  just  laid 
down,  which  it  would  appear  to  be.     Precisely  the  same  may  be  said 
in  regard  to  the  extension  of  a  coral  mass  ;  for  this  is  accomplished 
by  the  multiplication  of  polypes,  by  a  process  of  budding  from  the 
original  ;  and  yet  these  remain  connected  with  other,  so  as  to  form  a 
compound  whole,  bearing  a  strong  analogy  to  a  tree.     The  same 
cannot  be  said,  however,  of  the  extension  of  a  sea- weed,  for  this  can- 
not be  regarded  as  composed  of  a  collection  of  distinct  individuals; 
and  we  may  therefore  consider  it  as  an  illustration  of  the  tendency 
to  indefiniteness  in  point  of  size^  which  has  been  already  pointed  out 
in  regard  to  fornix  as  characteristic  of  the  lower  grades  of  organized 
structure,  and  as  therefore  leading  us  towards  the  inorganic  world. 
Where  this  is  the  case,  we  find  that  the  increase  depends,  as  in 
Minerals,  upon  the  multiplication  of  similar  parts.     Thus,  in  the  sea- 
weed, each  portion  of  the  frond   is  almost  a  precise  repetition   of 
ev^ery  other;   and  there  is  scarcely  any  of  that  mutual  dependence 
among  the  diflferent  parts,  which  makes  up  our  idea  of  one  individual. 
4.  It  is,  however,  in  the  internal  arrangement  or  aggregation  of  the 
particles,  respectively  composing  Organized  structures  and  Inorganic 
masses,  that  we   find  the   diflference  between   the  two  most  strongly 
marked.     Every  particle  of  a  Mineral  body  (in  which  there  has  not 
been  a  mixture  of  ingredients)  exhibits  the  same  properties  as  those 
possessed  by  the  whole  ;   so  that  the  chemist,  in  experimenting  with 
any  substance,  cares  not,  except  as  a  matter  of  convenience  merely, 
whether  a  grain  or  a  ton  be  the  subject  of  his  researches.     The  mi- 
nutest atom  of  carbonate  of  lime,  for  instance,  has  all  the  properties 
of  a  crystal  of  this  substance,  were  it  as  large  as  a  mountain.    Hence 
we  are  to  regard  a  mineral  body  as  made  up  of  an  indefinite  number 
of  constituent  particles,  similar  to  it  and  to  each  other  in  properties, 
and  having  no  further  relation  among  themselves  than  that  w^hich  they 
derive  from  their  juxtaposition.    Eachparticle,  then,  maybe  considered 
as  possessing  a  separate  individuality ;  as  w^e  can  predicate   of  its 
properties  all  that  can  be  said  of  the  largest  mass.     The  organized 
structure,  on  the  other  hand,  receives  its  designation  from  being  made 
up  of  a  number  of  distinct  parts  or  organs,  each  of  which  has  a  tex- 


20  NATURE  AND  OBJECTS  OF  THE 

ture  or  consistence  peculiar  to  itself;  and  it  derives  its  character  from 
the  whole  of  these  collectively.  Every  one  of  these,  as  we  shall 
hereafter  see,  is  the  instrument  of  a  certain  action  or  function,  which 
it  performs  under  certain  conditions  ;  and  the  concurrence  of  all 
these  actions  is  required  for  the  maintenance  of  the  structure  in  its 
normal  or  regular  state,  and  for  the  prevention  or  the  reparation  of 
those  changes,  which  chemical  and  physical  forces  would  otherwise 
speedily  produce  in  it,  from  causes  hereafter  to  be  explained.  Hence 
there  is  a  relation  oi  mutual  dependence  among  the  parts  of  an  Organ- 
ized structure  ;  which  is  quite  distinct  from  that  of  mere  proximity. 
Thus,  the  perfect  plant,  which  has  roots,  stem,  and  leaves,  is  an  ex- 
ample of  an  organized  structure,  in  which  the  relation  of  the  different 
parts  to  the  integrity  of  the  whole  is  sufficiently  obvious  ;  since,  when 
entirely  deprived  of  either  set  of  them,  the  plant  must  perish,  unless 
it  have  within  itself  the  power  of  replacing  them. 

5.  In  the  lower  animals,  as  in  vegetables,  we  find  a  marked  tend- 
ency to  the  repetition  of  similar  parts,  which  shows  an  evident  affi- 
nity to  the  mineral  kingdom ;  and  this  not  only  in  a  composite  tree, 
or  in  a  coral  mass,  which,  as  just  stated,  must  be  considered  as  an 
aggregation  of  distinct  individuals;  but  also  in  many  animals,  which 
cannot  be  divided  without  the  destruction  of  their  lives, — especially 
among  the  Radiated,  and  the  lower  Articulated  tribes.  Where  such 
a  repetition  exists,  some  of  the  organs  may  be  removed  without  per- 
manent injury  to  the  structure  ;  their  function  being  performed  by 
those  that  remain.  Thus,  it  is  not  uncommon  to  meet  with  specimens 
of  the  common  five-rayed  starfish,  in  which  not  only  one  or  two,  but 
even  three  or  four,  of  the  arms  have  been  lost  without  the  destruction 
of  the  animal's  life;  and  this  is  the  more  remarkable,  as  the  arms  are 
not  simply  organs  of  locomotion  or  prehension,  but  contain  prolonga- 
tions of  the  stomach.  In  the  bodies  of  the  higher  animals,  however, 
where  there  are  few  or  no  such  repetitions,  and  where  there  is  conse- 
quently a  greater  diversity  in  character  and  function  between  the 
different  organs,  the  mutual  dependence  of  their  actions  upon  one 
another  is  much  greater,  and  the  loss  of  a  single  part  is  much  more 
likely  to  endanger  the  existence  of  the  whole.  Such  structures  are 
said  to  be  more  highly  organized  than  those  of  the  lower  classes ; 
not  because  the  whole  number  of  parts  is  greater, — for  it  is  fre- 
quently much  less ;  but  because  the  number  of  dissimilar  parts,  and 
the  consequent  adaptation  to  a  variety  of  purposes,  is  much  greater, 
— the  principle  of  division  of  labour,  in  fact,  being  carried  much 
further,  a  much  larger  class  of  objects  being  attained,  and  a  much 
greater  perfection  in  the  accomplishment  of  them  being  thus  provided 
for. 

6.  Keeping  in  view,  then,  what  has  just  been  stated  in  regard  to 
the  divisibility  of  a  Tree  or  a  Zoophyte  into  a  number  of  parts,  each 
capable  of  maintaining  its  own  existence,  we  may  trace  a  certain  gra- 
dation from  the  condition  of  the  Mineral  body  to  that  of  the  highest 
Animal,  in  regard  to  the  character  in  question.     Thus  the  individu- 


SCIENCE  OF  PHYSIOLOGY. 


34 


I 


ality  of  a  Mineral  substance  may  be  said  to  reside  in  each  molecule ; 
that  of  a  Plant  or  Zoophyte,  in  each  member;  and  that  of  one  of  the 
higher  Animals,  in  the  sum  of  all  the  organs.  The  distinction  is 
much  greater,  however,  between  the  lowest  organized  fabric  and  any 
mineral  body,  than  it  is  between  the  highest  and  the  lowest  organized 
structures  ;  for,  as  we  shall  hereafter  see,  the  highest  and  most  com- 
plicated may  be  regarded  as  made  up  of  an  assemblage  of  the  lowest 
and  simplest ;  whose  structure  and  actions  have  been  so  modified  as 
to  render  them  mutually  dependent ;  but  which  yet  retain  a  separate 
individuality,  such  as  enables  them  to  continue  performing  their 
functions  when  separated  from  the  mass,  so  long  as  the  proper  con- 
ditions are  supplied. 

7.  Between  the  very  simplest  organized  fabric,  and  every  form  of 
mineral  matter,  there  is  a  marked  difference  in  regard  to  intimate 
structure  and  consistence.  Inorganic  substances  can  scarcely  be  re- 
garded as  possessing  a  structure  ;  since  (if  there  be  no  admixture  of 
components)  they  are  uniform  and  homogeneous  throughout,  whether 
they  be  existing  in  the  solid,  liquid,  or  gaseous  form  ;  being  composed 
of  similar  particles,  held  together  by  attractions  which  affect  all  alike. 
Far  different  is  the  character  of  Organized  structures ;  for  in  the 
minutest  parts  of  these  may  be  detected  a  heterogeneous  composition, — 
a  mixture  of  solid  and  fluid  elements,  which  are  so  intimately  combined 
and  arranged,  as  to  impart  such  peculiarities  to  the  tissues,  even  in 
regard  to  their  physical  properties,  as  we  never  encounter  amongst 
Mineral  bodies.  In  the  latter,  solidity  or  hardness  may  be  looked 
upon  as  the  characteristic  condition  ;  whilst  in  Organized  structures, 
softness  (resulting  from  the  large  proportion  of  fluid  components)  may 
be  considered  the  distinctive  quality,  being  most  obvious  in  the  parts 
that  are  most  actively  concerned  in  vital  operations.  This  softness  is 
evidently  connected  with  the  roundness  of  form  characteristic  of 
organized  fabrics,  w^hich  is  most  evident  when  the  tissues  contain  the 
greatest  proportion  of  fluid  ;  whilst  the  plane  surfaces  and  angular 
contours  of  mineral  bodies  are  evidently  due  to  the  mode  in  which 
the  solid  particles  are  aggregated  together,  without  any  intervening 
spaces. 

8.  The  greatest  solidity  exhibited  by  Organized  fabrics  is  found 
where  it  is  desired  to  impart  to  them  the  simple  physical  property  of 
resistance ;  and  this  is  attained  by  the  deposition  of  solid  particles, 
usually  of  a  mineral  character,  in  tissues  that  were  originally  soft  and 
yielding.  It  is  in  this  manner  that  the  almost  jelly-like  substance,  in 
which  all  the  organs  of  animals  originate,  becomes  condensed  inlo 
cartilage,  and  that  the  cartilage  is  afterwards  converted  into  bone  ;  it 
is  in  the  same  manner,  also,  that  the  stones  of  fruit,  and  the  heart- 
wood  of  timber-trees,  are  formed  out  of  softer  tissues.  But,  as  we 
shall  hereafter  see,  this  kind  of  conversion,  whilst  it  renders  the  tissue 
more  solid  and  durable,  cuts  it  off  from  any  active  participation  in  the 
vital  operations;  and  thence  reduces  it  to  a  state  much  more  nearly 
analogous  to  that  of  mineral  bodies.     This  resemblance  is  rendered 


22  NATURE  AND  OBJECTS  OF  THE 

more  close  by  the  fact,  that  the  earthy  deposits  frequently  retain  a 
distinctly  crystaline  condition  ;  so  that,  when  they  are  present  in  large 
proportion,  they  impart  a  more  or  less  crystaline  aspect  to  the  mass, 
and  especially  a  crystaline  mode  of  fracture,  which  is  evident  enough 
in  many  shells.  It  must  not  be  hence  concluded,  however,  that  such 
substances  are  of  an  inorganic  nature  ;  all  that  is  shown  by  their  crys- 
taline structure  being,  that  the  animal  basis  exists  in  comparatively 
small  amount,  and  that  the  mode  in  which  the  mineral  matter  w^as 
deposited  has  not  interfered  with  its  crystaline  aggregation. 

9.  It  is  not  to  be  disputed  that  a  certain  degree  of  homogeneity  is 
apparently  to  be  found  in  the  minutest  elements,  into  which  certain 
organized  tissues  are  to  be  resolved.  Thus,  in  the  membranes  vf\\\c\i 
form  the  walls  of  Animal  and  Vegetable  cells^  the  highest  powers  of 
the  microscope  fail  in  directing  any  such  distinction  of  fluid  and  solid 
components,  as  that  which  has  been  described  as  characteristic  of 
organized  structures.  Nevertheless  it  is  indubitable  that  such  distinct 
components  must  exist;  and  this  especially  from  the  properties  of  these 
membranes  in  regard  to  water.  For  it  is  one  of  the  most  remarkable 
facts  in  the  whole  range  of  science,  that  a  membrane,  in  which  not 
the  slightest  appearance  of  a  pore  can  be  discovered  under  the  highest 
powers  of  the  microscope,  should  be  traversed  by  water  ;  and  that, 
too,  with  no  inconsiderable  rapidity.  The  change  which  these  mem- 
branes undergo  in  drying  is  another  proof  that  they  are  not  so  homo- 
geneous as  they  appear,  and  that  water  is  an  element  of  their  structure, 
not  merely  chemically,  but  mechanically.  The  same  may  be  said  in 
regard  to  the  fibres^  which  form  the  apparently  ultimate  elements  of 
the  simple  fibrous  tissues  in  Animals,  and  which  are  also  met  with  in 
the  interior  of  certain  cells  and  vessels  in  Plants.  These  fibres  would 
appear  to  be  of  perfectly  simple  structure;  yet  we  know  from  the  loss 
of  fluid,  and  the  change  of  properties,  which  they  undergo  in  drying, 
that  water  must  have  formed  part  of  their  substance. — It  may  be 
remarked,  however,  in  regard  to  both  these  elementary  forms  of 
organized  tissue,  that  the  simplicity  of  their  function  is  in  complete 
conformity  w^ith  the  apparent  homogeneousness  of  their  structure  ;  for 
the  cell-membrane  is  chiefly  destined  to  act,  like  the  porous  septum 
in  certain  forms  of  the  voltaic  battery,  as  a  boundary-wall  to  the  con- 
tained fluid,  without  altogether  interfering  with  its  passage  elsewhere; 
the  forces  which  produce  its  imbibition  or  expulsion  being  probably 
situated,  not  in  this  pervious  wall,  but  in  the  cavity  which  it  bounds. 
And,  in  the  same  manner,  the  function  of  the  fibrous  tissues,  to  which 
allusion  was  just  now  made,  is  of  an  entirely  physical  character  ;  being 
simply  to  resist  strain  or  pressure,  and  yet  to  allow  of  a  certain  degree 
of  yielding  by  their  elasticity. 

10.  In  all  cases  in  w^hich  active  vital  operations  are  going  on,  we 
can  make  a  very  obvious  distinction  of  the  structures  subservient  to 
them,  into  liquid  and  solid  parts  ;  and  it  is,  indeed,  by  the  continual 
reaction  which  is  taking  place  between  these,  that  the  fabric  is  main- 
tained in  its  normal  condition.     For,  as  we  shall  hereafter  see,  it  is 


SCIENCE  OF  PHYSIOLOGY.  g|| 

liable  to  a  constant  decomposition  or  separation  into  its  ultimate  ele- 
ments ;  and  it  is  consequently  necessary  that  the  matters  which  have 
undergone  that  disintegration  should  be  carried  off,  and  that  they  should 
be  replaced  by  new  particles.  These  processes  of  removal  and  re- 
placement, with  the  various  actions  subservient  to  them,  make  up  a 
large  proportion  of  the  life  of  all  Organized  beings.  Now  as  all  the 
alimentary  matter  must  be  reduced  to  the  liquid  form,  in  order  that  it 
may  be  conveyed  to  the  situations  in  w^hich  it  is  required,  and  as  all 
the  decomposed  or  disintegrated  matter  must  be  reduced  to  the  same 
form  in  order  to  be  carried  off,  the  intermingling  or  mutual  penetra- 
tion of  solids  and  liquids  in  the  minutest  parts  of  the  body  is  at  once 
accounted  for.  We  shall  hereafter  see  that  a  cell^  or  closed  vesicle, 
formed  of  a  membranous  wall,  and  containing:  fluid,  maybe  regarded 
as  the  simplest  form  of  a  living  body,  and  tne  simplest  independent 
part  or  instrument  of  the  more  complex  fabrics  (§  30). 

11.  Organized  structures  are  further  distinguished  from  Inorganic 
masses,  by  the  peculiarity  of  their  chemical  constitution.  This  pecu- 
liarity does  not  consist,  however,  in  the  presence  of  any  elementary 
substances,  which  are  not  found  elsewhere ;  for  all  the  elements,  of 
which  organized  bodies  are  composed,  exist  abundantly  in  the  world 
around.  It  might  have  been  supposed  that  beings  endowed  with  such 
remarkable  powers  as  those  of  Animals  and  Plants, — powers  which 
depend,  as  we  shall  hereafter  see,  upon  the  exercise  of  properties  to 
which  we  find  nothing  analogous  in  the  Mineral  world, — would  have 
had  an  entirely  different  material  constitution  ;  but  a  little  reflection 
will  show,  that  the  identity  of  the  ultimate  elements  of  Organized 
structures  with  those  of  the* Inorganic  world,  is  a  necessary  conse- 
quence of  the  mode  in  which  the  former  are  built  up.  For  that  which 
the  parent  communicates,  in  giving  origin  to  a  new  being,  is  not  so 
much  the  structure  itself,  as  the  power  of  forming  that  structure  from 
the  surrounding  elements;  audit  is  by  gradually  drawing  to  itself 
certain  of  these  elements,  that  the  germ  becomes  developed  into  the 
complete  fabric.  Now,  of  the  fifty-jive  simple  or  elementary  sub- 
stances, which  are  known  to  occur  in  the  Mineral  world,  only  about 
eighteen  or  nineteen  are  found  in  Plants  and  Animals ;  and  many  of 
these  in  extremely  minute  proportion.  Some  of  these  appear  to  be 
merely  introduced  to  answer  certain  chemical  or  mechanical  purposes ; 
and  the  composition  of  the  parts  w^hich  possess  the  highest  vital  en- 
dowments, is  for  the  most  part  simpler  and  more  uniform. 

12.  The  actual  tissues  of  Plants,  when  entirely  freed  from  the  sub- 
stances they  may  contain,  have  been  found  to  possess  a  very  uniform 
composition,  and  to  agree  in  their  chemical  properties.  The  substance 
which  is  left  after  the  action,  upon  any  kind  of  Vegetable  tissue,  of 
such  solvents  as  are  fitted  to  dissolve  out  the  matters  deposited  in  its 
cavities  and  interstices,  is  termed  Cellulose.  It  consists  of  24  Carbon, 
21  Hydrogen,  and  21  Oxygen ;  or,  in  other  words,  of  Carbon  united 
to  the  elements  of  w^ater,  in  the  proportion  of  eight  of  the  former  to 
seven  of  the  latter.     It  may  be  very  easily  converted  into  gum  or 


24  NATURE  AND  OBJECTS  OF  THE 

sugar,  by  Chemical  processes,  which  effect  the  removal  or  the  addi- 
tion of  the  elements  of  water.  Now  there  is  no  compound  known  to 
exist  in  the  Inorganic  world,  which  bears  the  remotest  analogy  to  this ; 
and  we  have  no  reason  to  believe  that  it  could  be  produced  in  any 
other  way,  than  by  that  peculiar  combination  of  forces  which  exists  in 
the  growing  Plant. 

13.  In  like  manner,  a  large  proportion  of  the  Animal  tissues,  espe- 
cially those  most  actively  engaged  in  the  operations  of  nutrition,  have 
a  nearly  uniform  composition,  when  freed  from  the  substances  they 
contain.  We  may  distinguish  among  them  two  chiei proximate  prin- 
ciples, which  appear  under  various  modifications  in  a  great  variety  of 
dissimilar  parts,  and  which  seem  capable  of  conversion  into  other 
principles  by  the  addition  or  subtraction  of  some  of  their  constituents. 
The  first  and  most  important  of  these,  named  Proteine,  consists  of  40 
Carbon,  31  Hydrogen,  5  Nitrogen,  and  12  Oxygen ;  and  although  its 
composition  is  so  complex,  it  appears  to  act  like  a  simple  body,  in 
uniting  with  Oxygen,  Acids,  &c.,  in  definite  proportions,  as  well  as 
with  Sulphur  and  Phosphorus; — with  which  last,  indeed,  it  is  always 
found  combined,  in  the  Albumen,  Fibrin,  &c.,  that  are  commonly 
regarded  as  the  organic  constituents  of  the  Animal  tissues.  The 
second  of  the  chief  proximate  principles,  termed  Gelatine,  is  largely 
diffused  through  the  Animal  body  ;  but  there  is  much  uncertainty 
whether  it  exists  in  a  condition  that  can  be  properly  termed  organized, 
or  whether  it  is  a  mere  deposit,  possessing  a  definite  form,  like  many 
of  the  deposits  in  the  Vegetable  tissues.  It  consists  of  13  Carbon, 
10  Hydrogen,  2  Nitrogen,  and  5  Oxygen;  and  it  is  principally  cha- 
racterized by  its  solubility  in  hot  water;  and  by  the  insolubility  of  its 
compound  with  tannic  acid. 

14.  We  shall  hereafter  dwell  more  in  detail  upon  the  Chemical 
Constitution  of  the  Animal  tissues  and  products  (Chap.  III).  These 
substances  are  only  noticed  here,  in  illustration  of  the  general  state- 
ment, that  the  proximate  principles  of  Animal  and  Vegetable  bodies, — 
that  is,  the  simplest  forms  to  which  their  component  structures  can 
be  reduced,  without  altogether  separating  them  into  their  ultimate 
elements, — are  of  extremely  peculiar  constitution ;  being  made  up  of 
three  elements  in  Plants,  or  four  in  Animals;  of  which  the  atoms  do 
not  seem  to  be  united  two  by  two,  or  by  the  method  of  binary  com- 
position;  but  of  which  a  large  number  are  brought  together  to  form 
one  compound  atom,  of  ternary  or  quaternary  composition.  This  com- 
pound atom,  like  Cyanogen,  and  many  others  derived  from  Organic 
products,  acts  like  a  simple  or  elementary  one  in  its  combinations 
with  other  substances.  It  is  worthy  of  remark  that,  in  this  respect 
as  in  others,  the  Vegetable  kingdom  is  intermediate  between  the 
Animal  and  the  Mineral.  For  the  two  bases  of  the  Animal  tissues, 
whose  composition  has  been  just  given,  are  remarkable  not  only  for 
containing  ybwr  elements,  but  for  the  very  large  number  of  atoms  of 
each  which  enter  into  the  single  compound  atom  of  the  Proteine  or 
Gelatine ;  and  the  proportions  of  these  elements  to  each  other  are  not 


SCIENCE  OF  PHYSIOLOGY.  39^ 

such,  as  to  lead  to  the  suspicion  that  the  compound  atom  may  be 
regarded  as  made  up  of  simpler  ones,  united  together  in  the  manner  of 
the  acids  and  bases  of  Inorganic  Chemistry.  On  the  other  hand,  the 
Cellulose  of  Plants  is  much  simpler  in  its  composition,  since  it 
includes  only  three  elements,  and  the  numbers  which  represent  their 
proportions  are  smaller;  whilst  these  proportions  are  themselves  such, 
as  suggest  the  idea  of  simplicity  in  their  method  of  combination, — the 
union  of  water  and  carbon  in  the  common  binary  method.  This  idea 
is  confirmed  by  the  mode  of  the  original  production  of  cellulose,  which 
indicates  a  direct  union  of  carbon  with  water;  as  well  as  by  the  fact, 
that  the  chemical  difference  between  cellulose  and  numerous  other 
substances  found  in  Plants,  may  be  represented  by  the  simple  addition 
or  subtraction  of  a  certain  number  of  atoms  of  water ;  and  that  the 
chemist  can  effect  an  actual  conversion  of  the  former  into  certain  of 
the  latter,  by  means  which  are  calculated  to  effect  such  an  addition 
or  subtraction. 

15.  We  shall  hereafter  see  that  Vegetables  are  intermediate  be- 
tween the  Animal  kingdom  and  the  Inorganic  world  in  another  most 
important  particular — the  nature  of  the  Chemical  operations  they 
effect ;  for,  although  their  own  organized  tissues  uniformly  have  the 
composition  of  Cellulose,  they  nevertheless  have  the  power  of  secret- 
ing and  storing  up,  in  the  interstices  of  these  tissues,  compounds 
which  are  nearly  or  exactly  identical  with  animal  Proteine  in  com- 
position and  properties:  and  they  derive  the  materials  for  these  com- 
pounds— the  quaternary  as  well  as  the  ternary — directly  from  the 
Inorganic  world  ;  being  endowed  with  the  wonderful  power  of  elabo- 
rating them  from  the  carbonic  acid,  water,  and  ammonia,  supplied  by 
the  atmosphere  and  by  the  soil  in  which  they  are  implanted.  On  the 
other  hand,  Animals  possess  no  such  power;  they  are  entirely  de- 
pendent upon  Plants  for  their  alimentary  materials ;  and  they  employ 
for  the  building-up  of  their  own  structures,  not  the  tissues  of  Plants, 
but  the  substances  secreted  by  them. 

2.   Of  Vital  Actions. 

16.  We  are  now  arrived  at  the  second  head  of  our  inquiry, — 
namely  the  nature  of  those  actions,  which  distinguish  living  beings 
from  masses  of  inert  matter,  and  which  are  designated  as  Vital,  to 
point  out  their  distinctness  from  Physical  and  Chemical  phenomena. 
There  can  be  no  doubt  whatever,  that,  of  the  many  changes  which 
take  place  during  the  life,  or  state  of  vital  activity,  of  an  Organized 
being,  and  which  intervene  between  its  first  development  and  its 
final  decay,  a  large  proportion  are  effected  by  the  agency  of  those 
forces,  which  operate  in  the  Inorganic  world  ;  and  there  is  no  neces- 
sity whatever  for  the  supposition,  that  these  forces  have  any  other 
operation  in  the  living  body  than  they  would  have  out  of  it  under 
similar  circumstances.  Thus  the  propulsion  of  the  blood  by  the 
heart  through  the  large  vessels,  is  a  phenomenon  precisely  analogous 


26  NATURE  AND  OBJECTS  OF  THE 

to  the  propulsion  of  any  other  liquid  through  a  system  of  pipes  by 
means  of  a  forcing  pump  ;  and  if  the  arrangement  of  the  tubes,  the 
elasticity  of  their  walls,  the  contractile  power  of  the  heart,  and  the 
physical  properties  of  the  fluid,  could  be  precisely  imitated,  the  arti- 
ficial apparatus  would  give  us  an  exact  representation  of  the  actions 
of  the  real  one.  The  motor  force  of  the  muscles  upon  the  bones, 
again,  operates  in  a  mode  that  might  be  precisely  represented  by  an 
arrangement  of  cords  and  levers  ;  the  peculiarity  here,  as  in  the  for- 
mer case,  being  solely  in  the  mode  in  which  the  force  is  first  gene- 
rated. So,  again,  the  digestive  operations  which  take  place  in  the 
stomach  are  capable  of  being  closely  imitated  in  the  laboratory  of  the 
chemist:  when  the  same  solvent  fluid  is  employed,  and  the  same 
agencies  of  heat,  motion,  &c.,  are  brought  into  play.  Moreover  we 
shall  hereafter  see  reason  to  believe,  that  the  peculiar  form  of  Capillary 
Attraction,  to  which  the  term  Endosmose  is  applied,  performs  an 
important  part  in  the  changes  which  are  continually  taking  place  in 
the  living  body. 

17.  But  after  every  possible  allowance  is  made  for  the  operation 
of  Physical  and  Chemical  forces,  in  the  living  Organism,  there  still 
remain  a  large  number  of  phenomena,  which  cannot  be  in  the  least 
explained  by  them,  and  which  we  can  only  investigate  with  success, 
when  we  regard  them  as  resulting  from  the  agency  of  forces  as  dis- 
tinct from  those  of  Physics  and  Chemistry,  as  they  are  from  each 
other.  It  is  to  these  phenomena  that  we  give  the  name  of  Vital;  the 
forces  from  whose  operation  we  assume  them  to  result,  are  termed 
vital  forces  ;  and  the  properties,  which  we  must  attribute  to  the  sub- 
stances exerting  those  forces,  are  termed  vital  properties.  Thus  we 
say  that  the  act  of  contraction  in  a  Muscle  is  a  vital  phenomenon ;  be- 
cause its  character  appears  totally  distinct  from  that  of  a  Physical  or 
Chemical  action  ;  and  because  it  is  dependent  upon  other  vital  changes 
in  the  muscular  substance.  The  act  is  the  manifestation  of  a  certain 
force^  the  possession  of  which  is  peculiar  to  the  muscular  structure, 

and  which  is  named  the  Contractile  force.  Further,  that  force  may 
remain  (as  it  were)  dormant  in  the  muscular  structure,  not  manifest- 
ing itself  for  a  great  length  of  time,  and  yet  capable  of  being  called 
into  operation  at  any  moment;  and  this  dormant  force  is  termed  a 
property ;  thus  we  regard  it  as  the  essential  peculiarity  of  living  Mus- 
cular tissue,  that  it  possesses  the  vital  property  of  Contractility.  Or, 
to  reverse  the  order,  the  muscle  is  said  to  possess  the  property  of 
Contractility ;  the  property  called  into  operation  by  the  appropriate 
stimulus  gives  rise  to  the  Contractile  Force ;  and  the  Force,  produces, 
if  its  operation  be  unopposed,  the  act  of  Contraction. 

18.  It  may  be  said  that  the  distinction  here  made  is  a  verbal  one ; 
and  that  a  very  simple  thing  is  thus  made  complex  :  but  it  will  be 
presently  seen  that  it  is  necessary,  in  order  to  enable  us  to  take  cor- 
rect views  of  the  nature  of  Vital  phenomena,  and  to  understand  their 
analogies  with  those  of  the  Inorganic  world.  And,  in  fact,  the  dis- 
tinction between  the  property ^  the  force^  and  the  action^  becomes  ap- 


SCIENCE  OF  PHYSIOLOGY.  gfJT 

parent  upon  a  little  consideration.  Of  the  property  we  are  altogether 
unconscious,  so  long  as  it  is  not  called  into  exercise ;  we  could  not, 
for  example,  determine  by  the  simple  exercise  of  any  of  our  senses, 
whether  a  certain  piece  of  muscle  retained,  or  had  lost  its  contrac- 
tility. When  the  property  is  called  into  action  by  its  appropriate 
stimulus,  we  may  convince  ourselves  that  a  force  is  generated,  even 
if  no  sensible  action  is  prevented;  thus,  if  we  were  to  hold  the  two 
extremities  of  a  muscle  so  firmly,  as  to  prevent  them  from  approxi- 
mating in  the  least  degree  when  its  contractility  was  excited,  we 
should  be  conscious  of  a  powerful  force  tending  to  draw  our  hands 
together ;  and  we  might  measure  the  amount  of  that  force,  by  me- 
chanical means  adapted  to  determine  the  weight  it  would  sustain. 
And  lastly,  if  no  obstacle  be  interposed  to  the  act  of  Contraction,  it 
then  becomes  obvious  to  our  senses,  by  the  change  in  the  shape  of 
the  muscle,  and  by  the  approximation  of  its  two  extremities,  as  well 
as  of  the  bodies  to  which  they  are  attached. 

19.  The  advantage  of  this  method  of  viewing  the  phenomena  of 
Life  is  best  shown,  by  turning  our  attention  for  a  moment  to  the 
mode  of  investigation  practised  in  Physics  and  Chemistry.  Thus, 
when  a  stone  falls  towards  the  earth,  we  say  that  this  is  an  act  or 
phenomenon  of  Gravitation.  The  force  with  which  the  stone  tends 
to  fall  to  the  ground,  whether  it  actually  falls  or  not,  is  called  the 
force  of  Gravitation  ;  and  the  property,  by  the  exercise  of  which  that 
force  is  generated,  is  called  the  property  of  Gravitation.  Now,  from 
observation  of  the  moon's  motion  it  is  shown  that  she  too  descends 
towards  the  earth  by  an  act  of  Gravitation ;  and  that  she  does  so  with 
a  certain  force,  which,  acting  in  conjunction  with  her  tangential  or 
centrifugal  force,  produces  her  movement  in  an  elliptical  orbit  round 
the  earth  ;  which  force  is  the  result  of  the  exercise  of  her  property  of 
Gravitation.  Could  we  conceive  the  Earth  to  be  withdrawn,  or  an- 
nihilated, the  property  of  Gravitation  would  still  exist  in  the  stone, 
or  in  the  Moon's  mass ;  but  the  force  would  be  extinct,  for  want  of 
the  excitement  of  the  property  ;  and  the  action  would  consequently 
not  take  place. — Now,  it  may  be  further  established  from  Astronomi- 
cal observation,  that  not  only  does  the  Moon  gravitate  towards  the 
Earth,  but  the  Earth  gravitates  towards  the  Moon;  so  that,  if  the  two 
bodies  were  entirely  free  from  the  action  of  all  other  forces,  they 
would  fall  towards  each  other  (the  distance  traversed  by  each  being 
in  proportion  to  the  size  of  the  other),  and  would  meet  in  their  com- 
mon centre  of  Gravity.  Hence  it  is  evident  that  the  attractive  force 
is  similar  in  both  bodies ;  and  our  idea  of  the  property  of  Gravitation 
must  be  extended,  therefore,  from  the  Earth  to  the  Moon.  Again, 
we  find  ample  reason  to  believe  that  the  same  force  acts  between 
the  Sun  and  the  Planets, — between  the  Planets  and  the  Sun, — and 
amongst  the  Planets  themselves ;  and  further,  careful  experiment 
shows  that  masses  of  matter  upon  the  Earth's  surface  are  not  only 
attracted  by  it,  and  attract  it  in  their  turn,  but  that  they  attract  and  are 
attracted  by  each  other.     Hence  we  arrive  at  the  idea  of  the  univer- 


28  NATURE  AND  OBJECTS  OF  THE 

sality  of  this  property  of  mutual  attraction ;  and  we  perceive  that,  in 
spite  of  the  varieties  in  the  actions  it  produces,  and  of  the  differences 
in  the  amounts  of  the  forces  to  which  it  gives  rise,  the  property  is  the 
same  throughout ;  so  that  we  can  predict  all  these  actions,  and  anti- 
cipate the  forces  which  will  be  developed,  from  the  simple  general 
expression  of  the  property  of  Mutual  Attraction,  and  of  the  conditions 
according  to  which  it  operates, — constituting  the  Law  of  Gravitation 
or  Mutual  Attraction. 

20.  Now  in  this  case  of  Mutual  Attraction,  we  have  no  opportu- 
nity of  witnessing  the  dormant  condition  of  the  property  in  any  mass 
of  matter ;  for,  as  nothing  is  wanting  but  the  presence  of  another 
mass  to  call  this  property  into  operation,  it  is  always  generating  force, 
and  giving  rise  to  actions.  If  we  could  conceive  of  the  existence  of 
but  a  single  mass  of  matter  in  the  universe,  we  shall  at  once  see  that, 
though  possessed  of  the  property  of  mutual  attraction,  it  would  not  be 
able  to  exercise  it  so  as  to  generate  an  attractive  force,  or  to  produce 
a  movement. 

21.  But  we  will  turn  to  another  case;  in  which  there  is  a  closer 
analogy  to  the  condition  of  living  beings ;  and  by  which,  therefore, 
the  view  here  put  forth  may  be  more  clearly  illustrated.  When  a 
magnet  (itself  a  bar  of  iron,  having  no  peculiarity  of  appearance), 
draws  towards  it  a  piece  of  iron,  we  may  say  that  a  Magnetic  action 
or  phenomenon  takes  place ;  further,  we  speak  of  the  power  which  pro- 
duces the  movement,  as  the  Magnetic  force ;  and  we  attribute  this 
force  to  a  certain  property  inherent  in  the  Magnet,  by  virtue  of  which 
it  draws  towards  itself  all  pieces  of  iron  that  are  within  the  sphere  of 
its  operation, — and  we  speak  of  the  iron  bar  as  endowed  with  the 
property  of  Magnetic  attraction.  Now  we  cannot  ascertain  the  pre- 
sence or  absence  of  this  property  in  a  certain  bar  of  iron,  by  any  dif- 
ference in  its  aspect,  its  specific  gravity,  its  chemical  properties,  nor, 
in  fact,  by  any  other  mode  than  the  putting  it  in  circumstances  adapted 
to  call  the  Magnetic  property  into  action  if  it  really  exist ;  thus  we  dip 
it  into  iron  filings,  and  judge  by  their  adhesion  whether  it  is  capable 
of  attracting  them  ;  or,  as  a  still  more  delicate  test,  we  ascertain  whe- 
ther it  is  capable  of  exerting  any  repulsive  power  on  a  delicately- 
suspended  needle  already  magnetized.  Again,  a  needle,  or  bar  of 
iron,  which  exhibits  this  magnetic  power  of  attracting  other  portions 
of  the  same  metal,  exhibits  another  power  which  would  seem  at  first 
sight  totally  distinct ;  namely,  that  of  constantly  turning  one  of  its 
extremities  towards  the  north,  and  the  other  towards  the  south,  when 
it  is  so  supported  as  to  be  free  to  do  so.  And  yet  there  is  no  doubt 
whatever,  that  this  directing  power  is  only  another  manifestation  of 
the  same  magnetic  attractiveness ;  depending  on  the  relation  between 
the  magnetized  bar,  or  needle,  and  the  Earth,  which  must  itself  be 
regarded  as  a  great  magnet.  Hence  the  idea  of  a  peculiar  kind  of 
mutual  attractiveness, — existing  in  a  limited  class  only  of  bodies, 
capable  of  being  excited  in  one  by  a  certain  agency  on  the  part  of  the 


SCIENCE  OF  PHYSIOLOGY.  29 

other,* — and  requiring  for  its  exercise  or  manifestation  a  certain  set 
of  conditions,  without  which  no  phenomenon  results, — is  that  which 
we  regard  as  fundamental  in  the  Science  of  Magnetism. 

22.  We  may  now  turn  from  these  departments  of  Physical  Science 
to  Chemistry;  and  here  we  shall  find  that  the  investigation  is  carried 
on  upon  the  very  same  plan.  In  fact,  the  whole  science  of  Chemistry 
is  founded  upon  the  idea  of  a  certain  attractiveness  or  affinity  existing 
among  the  ultimate  particles  or  molecules  of  the  different  elementary 
substances  ;  and  therefore  entirely  distinct  from  the  homogeneous  at- 
traction which  holds  together  the  particles  of  the  same  mass,  or  from 
the  gravitative  attraction,  which  operates  alike  upon  all  masses,  what- 
ever be  their  composition.  Thus  we  say  that  Sulphuric  acid  and  Pot- 
ash have  an  affinity  for  each  other;  because  they  unite  when  they  are 
brought  together,  and  form  a  new  compound.  This  is  a  Chemical  action 
or  phenomenon.  Now  we  know  that  they  tend  to  unite  with  a  cer- 
tain ybrce;  a  force,  however,  which  cannot  be  measured  mechanically, 
and  which  can  only  be  expressed  by  comparing  it  with  some  other 
force  of  the  same  kind.  Thus  we  say  that  the  mutual  affinity  of  Sul- 
phuric acid  and  Potash  is  greater  than  that  of  Nitric  acid  and  Pot- 
ash ;  because,  if  we  pour  Sulphuric  acid  upon  Nitrate  of  Potash,  the 
Sulphuric  acid  detaches  (as  it  were)  the  Potash  from  its  connection 
with  the  Nitric  acid,  forms  a  new  compound  with  it,  and  sets  the 
Nitric  acid  free.  Hence  we  say  that  it  is  a  property  of  Sulphuric 
acid  to  have  a  very  strong  affinity  for  Potash.  This  property  exists 
in  every  particle  of  Sulphuric  acid  that  exists,  whether  free  or  com- 
bined ;  but  it  remains  dormant,  until  it  is  called  into  operation  by  the 
contact  of  Potash ;  and  it  then  develops  a  force,  which  may  com- 
pletely change  the  combinations  previously  existing,  and  give  rise  to 
new  ones. 

23.  Now  of  this  property  we  are  not  informed  by  any  of  the  other 
properties  of  Sulphuric  acid ;  and  we  only  recognize  its  existence  by 
the  action  which  is  the  result  of  its  exercise.  If  a  new  element  or 
compound  be  discovered,  the  chemist  is  totally  unable  to  predict  its 
force  of  affinity  for  this  or  that  substance ;  and  he  can  only  guess  by 
analogy,  what  will  be  its  behaviour  under  various  circumstances. 
Thus  if  it  have  the  external  properties  of  a  Metal,  he  presumes  that 
it  will  correspond  with  the  Metals  in  possessing  a  strong  affinity  for 
oxygen,  sulphur,  &c.;  whilst  if  it  seem  analogous  to  Iodine,  Chlorine, 
&c.,  he  infers  that  it  will  be  a  suppprter  of  combustion,  that  it  will  form 
an  acid  with  hydrogen,  and  so  on.  But  even  though  such  guesses  may 
be  made  with  a  certain  amount  of  probability,  nothing  but  experience 
can  show  the  positive  degrees  of  affinity,  which  the  substance  may 
have  for  others  of  different  kinds ;  and  the  experimental  determina- 
tion can  only  be  made  by  observing  the  actions  of  the  body  when 
placed  in  different  circumstances,  from  which  we  judge  of  its  pro- 

*  As  when  one  magnet  ismade  by  another;  or  when  iron  rails,  pokers,  &c.,  become 
magnetic  by  the  influence  of  the  earth. 


30  NATURE  AND  OBJECTS  OF  THE 

perties,  and  of  the  forces  to  which  these  properties  give  rise  when 
they  are  called  into  operation. 

24.  It  is  hoped  that  the  propriety  of  the  distinct  use  of  the  terms 
vital  action,  vital  force,  and  vital  property ,  will  now  be  evident ;  and 
that  the  student  will  be  now  prepared  to  attach  distinct  ideas  to  each 
of  them.  It  is  the  business  of  the  Physiologist  to  study  those  actions 
or  phenomena  which  are  peculiar  to  living  beings,  and  which  are  hence 
termed  vital;  he  endeavours  to  trace  them  to  the  operation  of  the  fun- 
damental properties  of  organized  structures — ^just  as  the  Astronomer 
traces  all  the  movements,  regular  and  perturbed,  of  the  heavenly  bodies 
to  the  mutual  attraction  of  their  masses,  acting  concurrently  with 
their  force  of  onward  rectilinear  movement;  or  as  the  Chemist  attri- 
butes the  different  acts  of  combination  or  separation,  which  it  is  his 
province  to  study,  to  the  mutual  affinities  of  the  substances  concerned  : 
and  the  physiologist,  like  the  astronomer  or  the  chemist,  seeks  to  de- 
termine the  laws  according  to  which  these  properties  act,  or,  in  other 
words,  to  express  the  precise  conditions  under  which  they  are  called 
into  play,  and  the  forces  which  they  then  generate.  It  is  only  in  this 
manner,  that  Physiology  can  be  rightly  studied  and  brought  to  the 
level  of  other  sciences.  There  can  be  no  doubt  that  its  progress  has 
been  greatly  retarded  by  the  assumption  that  its  phenomena  were  all 
to  be  attributed  to  the  operation  of  some  general  controlling  agency,  or 
Vital  Principle;  and  that  the  laws  expressing  the  conditions  of  these 
phenomena  must  be  sought  for  by  methods  of  investigation  entirely 
distinct  from  those  which  are  employed  in  other  sciences.  But  a 
better  spirit  is  now  abroad ;  and  the  student  cannot  be  too  strongly 
urged  to  discard  any  ideas  of  this  kind  as  absolutely  untenable;  and 
to  keep  steadfastly  in  view,  that  the  laws  of  Vital  Action  are  to  be  at- 
tained in  the  same  manner  as  those  of  Physics  or  Chemistry, — that  is, 
by  the  careful  collection  and  comparison  of  vital  phenomena,  and  by 
applying  to  them  the  same  method  of  reasoning,  as  that  which  is  used 
in  determining  the  forces  and  properties  on  which  other  phenomena 
depend.  True  it  is,  that  we  can  scarcely  yet  hope  to  reach  the  same 
degree  of  simplification,  as  that  of  which  other  sciences  are  capable; 
and  this  on  account  of  the  very  complex  nature  of  the  phenomena 
themselves,  and  the  difficulty  of  satisfactorily  determining  their  con- 
ditions. The  uncertainty  of  the  results  of  Physiological  experiments 
is  almost  proverbial ;  that  uncertainty  does  not  result,  however,  from 
any  want  of  fixity  in  the  conditions  under  w^hich  the  vital  properties 
operate,  but  merely  from  the  influence  of  differences  in  those  condi- 
tions, apparently  so  slight  as  to  elude  observation,  and  yet  suflficiently 
powerful  to  produce  an  entire  change  in  the  result.  And,  owing  to 
that  mutual  dependence  of  the  different  actions  of  the  organized 
structure,  to  which  reference  has  been  already  made  (§  5),  we  cannot 
seriously  derange  one  class  of  these  actions,  without  also  deranging, 
or  even  suspending  others; — a  circumstance  which  obviously  renders 
vital  phenomena  much  more  difficult  of  investigation  than  those  of 
inorganic  matter. 


SCIENCE  OF  PHYSIOLOGY.  31 

25.  All  sciences  have  their  "  ultimate  facts ;"  that  is,  facts  for  which 
no  other  cause  can  be  assigned  than  the  Will  of  the  Creator.  Thus, 
in  physics,  we  cannot  ascend  above  the  fact  of  Attraction  (which  ope- 
rates according  to  a  simple  and  universal  law)  between  all  masses  of 
matter ;  and  in  chemistry,  we  cannot  rise  beyond  the  fact  of  Affinity 
(limited  by  certain  conditions  which  are  not  yet  well  understood) 
between  the  particles  of  different  kinds  of  matter.  When  we  say 
that  we  have  explained  any  phenomenon,  we  merely  imply  that  we 
have  traced  its  origin  to  these  properties,  and  shown  that  it  is  a  ne- 
cessary result  of  the  laws  according  to  which  they  operate.  For  the 
existence  of  the  properties,  and  the  determination  of  the  conditions, 
we  can  give  no  other  reason  than  that  the  Creator  willed  them  so  to 
be  ;  and,  in  looking  at  the  vast  variety  of  phenomena  to  which  they 
give  rise,  we  cannot  avoid  being  struck  with  the  general  harmony 
that  exists  amongst  them,  and  the  mutual  dependence  and  adaptation 
that  may  be  traced  between  them,  when  they  are  considered  as  por- 
tions of  the  general  economy  of  Nature. — There  is  no  difference  in 
this  respect  between  Physiology  and  other  sciences;  except  that  the 
number  of  these  (apparently)  ultimate  facts  is  at  present  greater  in 
physiology,  than  it  is  in  other  sciences,  because  we  are  not  at  present 
able  to  include  them  under  any  more  general  expression.  Thus  we 
find  a  certain  peculiar  endowment  existing  in  one  form  of  structure ; 
and  another  endowment,  equally  peculiar,  inherent  in  another;  but 
we  can  give  no  reason  why  the  structure  called  muscular,  should 
possess  contractility,  and  w'hy  the  structure  called  nervous  should  be 
capable  of  generating  and  conveying  the  force  which  excites  that 
contractility  to  action.  Each  of  these  facts,  therefore,  is  for  the  pre- 
sent the  limit  to  our  knowledge  ;  we  can  ascertain  the  conditions, 
according  to  which  the  muscular  contractility,  and  the  exciting  powder 
of  the  nerve,  are  called  into  operation,  and  can  form  some  estimate 
of  the  amount  of  the  forces  which  they  generate  ;  but  we  cannot  see 
clearly  that  they  are  necessarily  connected  by  any  common  tie,  such 
as  that  which  binds  together  the  planetary  masses,  at  the  same  time 
that  it  weighs  down  the  bodies  on  the  surface  of  the  earth  towards  its 
centre. 

26.  The  present  condition  of  Physiology,  however,  finds  its  parallel 
in  the  history  of  some  other  sciences,  in  which  there  was  an  equal 
number  of  such  facts  that  were  for  a  time  regarded  as  ultimate.  Thus, 
until  the  phenomena  of  Terrestrial  Magnetism  had  been  investigated, 
the  polar  direction  of  the  magnetic  needle,  its  dip,  and  its  variation, 
were  regarded  as  phenomena  altogether  distinct  from  the  phenomena 
of  attraction  and  repulsion  w^hich  are  exhibited  between  two  magnets  ; 
and  the  former  seemed  "  ultimate  facts,"  of  which  no  further  account 
could  be  given.  So,  also,  before  the  time  of  Newton,  the  movements 
of  celestial  and  terrestrial  bodies  were  supposed  to  be  entirely  desti- 
tute of  connection  with  each  other.  But,  as  the  knowledge  of  the 
Earth's  Magnetism  has  shown  that  the  direction,  variation,  and  dip 
of  the  compass  are  referable  to  the  very  polar  forces  which   show 


32  NATURE  AND  OBJECTS  OF  THE 

themselves  on  a  small  scale  when  two  magnets  are  brought  near  each 
other ;  and  as  the  mutual  attraction  of  the  earth  and  moon,  of  the  sun 
and  planets,  has  been  shown  to  result  from  the  same  property,  as  that 
which  draws  together  any  two  masses  that  are  freely  suspended  ;  so 
may  it  be  fairly  anticipated  that  an  increased  attention  to  vital  phe- 
nomena, and  a  more  philosophical  method  of  reasoning  upon  them, 
will  tend  towards  the  same  kind  of  generalization,  and,  therefore,  to 
the  simplification  of  the  principles  of  the  science. 

27.  To  satisfy  ourselves — as  some  have  done — with  attributing 
the  phenomena  of  Life  to  the  agency  of  a  "  Vital  Principle,"  is  cer- 
tainly a  very  easy  way  of  extricating  ourselves  from  the  difficult  path 
of  physiological  inquiry.  But  we  are  not  in  that  manner  conducted 
one  step  nearer  to  the  object  of  that  inquiry.  For  it  is  just  as  if,  after 
the  manner  of  the  Ancients,  we  were  to  attribute  the  movements  of 
the  heavenly  bodies  to  a  "  principle  of  motion,"  without  inquiring 
into  the  conditions  according  to  which  it  acts.  Now,  as  Modern 
Physics  show  that  all  these  varied  movements  (so  different  in  kind, 
that  no  two  of  the  heavenly  bodies  move  at  the  same  rate,  or  in  paths 
of  similar  curvature),  are  the  results  of  two  forces,  each  acting  accord- 
ing to  its  own  laws,  and  modifying  the  other ;  and  as  it  refers  these 
forces  to  the  exercise  of  simple  properties  of  matter ;  so  should  the 
Physiologist  seek  for  the  common  sources  of  the  phenomena  he  wit- 
nesses, and  for  the  properties  of  the  organized  structures,  by  the 
exercise  of  which  they  are  produced.  These  properties  do  not  differ 
more  from  those  which  he  elsewhere  encounters,  than  organized 
fabrics  differ  from  masses  of  inorganic  matter,  both  in  structure  and 
composition  ;  and  there  is  no  necessity,  therefore,  to  call  in  the  aid 
of  any  other  agency,  to  account  for  the  peculiar  endowments  of  those 
fabrics. 

28.  The  advocates  of  the  existence  of  a  separate  Vital  Principle, 
as  the  unknown  cause  of  the  phenomena  of  life,  rely  much  upon  the 
peculiar  adaptation,  which  may  be  observed  amongst  the  several 
actions  of  an  organized  being ;  and  upon  their  common  subserviency 
to  the  maintenance  of  the  integrity  of  the  structure,  and  to  the  repara- 
tion of  the  effects  of  disease  or  injury,  which  imparts  to  them  a  cha- 
racter of  unity  that  seems  to  be  wanting  elsewhere.  But  if  we  take 
a  general  survey  of  the  phenomena  of  the  universe  at  large,  we  shall 
find  the  adaptation  just  as  complete,  the  mutual  dependence  as  close, 
the  unity  of  the  whole  as  perfect.  And  as  the  Philosopher  can  do 
nought  else  than  attribute  this  harmony,  this  mutual  adaptation  and 
dependence,  this  unity  of  purpose,  in  the  phenomena  of  the  Macro- 
cosm or  Universe,  to  the  Infinite  VV'isdom  and  Power  of  the  Design- 
ing Mind,  so  must  he  depart  from  all  right  methods  of  reasoning,  to 
suppose  that  the  like  harmony,  adaptation,  and  unity  in  the  operations 
of  the  Microcosm^  or  little  world  in  his  own  body,  can  have  any  other 
source. 

29.  The  only  sense  in  which  the  term  "Vital  Principle"  can  be 
properly  used,  is  as  a  convenient  and  concise  expression  for  the  sum 


SCIENCE  OF  PHYSIOLOGY.  33 

total  (so  to  speak)  of  the  powers  which  are  developed  by  the  action 
of  the  Vital  properties  of  Organized  structures — these  being  not  yet 
fully  understood,  and  the  conditions  of  their  action  being  but  imper- 
fectly known.  In  this  manner  it  has  been  customary  to  talk  of  the 
principles  of  Gravity,  of  Electricity,  of  Magnetism,  &c.,  as  the  un- 
known causes  of  certain  phenomena,  which  seemed  to  be  connected 
by  the  same  general  conditions;  but  as  the  advance  of  Physical  sci- 
ence has  done  away  with  these  modes  of  expression,  by  referring  all 
the  phenomena  to  the  simple  properties  of  matter,  and  by  fixing  the 
conditions  under  which  they  occur,  so  should  we  aim  at  a  corre- 
sponding simplification  and  precision  in  Physiology.  The  use  of  a 
term  like  Vital  Principle,  even  in  the  restricted  sense  now  specified, 
is  attended  with  this  danger: — that  it  rather  checks  inquiry,  by  giving 
rise  to  the  idea  that  a  reference  to  the  agency  of  such  a  principle  is 
alone  sufficient  to  explain  the  phenomena  ;  and,  as  it  is  attended  wdth 
no  corresponding  advantage,  it  seems  preferable  to  discard  the  term 
altogether.  It  will  not  be  again  introduced,  therefore,  in  this  Trea- 
tise ;  the  object  of  which  is  to  place  the  student  in  possession  of 
what  has  been  ascertained  regarding  the  peculiar  or  vital  properties 
of  Organized  Tissues.  This  may  be  most  advantageously  effected, 
by  first  making  him  acquainted  with  the  general  history  of  the  series 
of  phenomena  exhibited  by  Living  Beings  of  the  simplest  character, 
and  by  then  tracing  these  phenomena,  so  far  as  possible,  to  their  hid- 
den sources.  For  this  purpose  w^e  must  have  recourse  to  the  sim- 
plest forms  of  Cryptogamic  Plants,  which  consist  of  mere  aggrega- 
tions of  cells,  every  one  of  which  may  be  regarded  as  a  distinct  indi- 
vidual, since  it  is  perfectly  independent  of  the  rest,  and  performsybr 
and  by  itself,  all  the  functions  of  Growth  and  Reproduction.  We 
shall  find,  then,  in  the  operations  of  the  simple  cell,  an  epitome,  as  it 
were,  of  those  of  the  highest  and  most  complex  Plant ;  whilst  those  of 
the  higher  Plants  bear  a  close  correspondence 
with  those  which  are  immediately  concerned 
in  the  Nutrition  and  Reproduction  of  the  Ani- 
mal body.  The  functions  peculiar  to  Animals, 
and  distinguishing  them  from  Plants,  must  be 
separately  considered. 

30.  A  Cell,  in  Physiological  language,  is  a 
closed  vesicle  or  minute  bag,  formed  by  a 
membrane,  in  w^hich  no  definite  structure  can 
be  discerned,  and  having  a  cavity,  which  may       ^.    ,   .   ,  .  ,     „    

'  'IT  •  o       1  Simple  isolated  cells,  con- 

contam  matters  of  variable  consistence,     ouch     taining  reproductive  moie- 
a  cell  constitutes  the  whole  organism  of  such 

simple  plants  as  the  Protococcus  vivalis  (Red  Snow),  or  Palmella 
cruenta  (Gory  Dew);  for  although  the  patches  of  this  kind  of  vege- 
tation which  attract  our  notice,  are  made  up  of  vast  aggregations  of 
such  cells,  yet  they  have  no  dependence  upon  one  another,  and  the 
actions  of  each  are  an  exact  repetition  of  those  of  the  rest.  In  such 
a  cell,  every  organized  fabric,  however  complex,  originates.  The 
3 


34  NATURE  AND  OBJECTS  OF  THE 

vast  tree^  almost  a  forest  in  itself,  and  the  feeling,  thinking,  intelli- 
gent man^  spring  from  a  germ,  that  differs  in  no  obvious  particular 
from  the  permanent  condition  of  one  of  these  lowly  beings.  But 
whilst  the  powers  of  the  latter  are  restricted,  as  we  shall  see,  to  the 
continual  multiplication  of  new  and  distinct  individuals  like  itself, 
those  of  the  former  enable  it  to  produce  new  cells  that  remain  in 
closer  connection  with  each  other;  and  these  are  gradually  converted, 
by  various  transformations  of  their  own,  into  the  diversified  elements 
of  a  complex  fabric.  The  most  highly  organized  being,  however, 
will  be  shown  to  consist  in  great  part  of  cells  that  have  undergone 
no  such  transformation,  amongst  which  the  different  functions  per- 
formed by  the  individual  in  the  case  just  cited,  are  distributed,  as  it 
were  ;  so  that  each  cell  has  its  particular  object  in  the  general  eco- 
nomy, whilst  the  history  of  its  own  life  is  essentially  the  same  as  if  it 
were  maintaining  a  separate  existence. 

31.  We  shall  now"  examine,  then,  the  history  of  the  solitary  cell  of 
the  Red  Snow%  or  of  any  other  equally  simple  plant,  from  its  first 
development  to  its  final  decay;  in  other  words,  we  shall  note  those 
Vital  Phenomena,  w^hich  are  as  distinct  from  those  of  any  inorganic 
body,  as  is  its  organized  structure  (simple  as  it  appears)  from  the 
mere  aggregation  of  particles  in  the  inert  mass.  In  the  first  place, 
the  cell  takes  its  origin  from  a  germ,  which  is  a  minute  molecule,  that 
cannot  be  seen  without  a  microscope  of  high  power.  This  molecule 
appears,  in  its  earliest  condition,  to  be  a  simple  homogeneous  par- 
ticle, of  spherical  form;  but  it  gradually  increases  in  size  ;  and  a  dis- 
tinction becomes  apparent  between  its  transparent  exterior  and  its 
coloured  interior.  Thus  we  have  the  first  indication  of  the  cell-wall, 
and  the  cavity.  As  the  enlargement  proceeds,  the  distinction  be- 
comes more  obvious;  the  cell-wall  is  seen  to  be  of  extreme  tenuity 
and  perfectly  transparent,  and  to  be  homogeneous  in  its  texture; 
whilst  the  contents  of  the  cavity  are  distinguished  by  their  colour, 
which  is  bright-red  in  the  species  just  mentioned,  but  more  com- 
monly green.  At  first  they,  too,  seem  to  be  homogeneous;  but  a 
finely  granular  appearance  is  then  perceptible  ;  and  a  change  gradu- 
ally takes  place,  which  seems  to  consist  in  the  aggregation  of  the 
minute  granules  into  molecules  of  more  distinguishable  size  and  form. 
These  molecules,  which  are  the  germs  of  new  cells,  seem  to  be  at 
first  attached  to  the  wall  of  the  parent-cell ;  afterwards  they  separate 
from  it  and  move  about  in  its  cavity;  and  at  a  later  period,  the 
parent-cell  bursts  and  sets  them  free.  Now,  this  is  the  termination 
of  the  life  of  the  parent-cell;  but  the  commencement  of  a  life  of  a 
new^  generation  ;  since  every  one  of  these  germs  may  become  de- 
veloped into  a  cell,  after  precisely  the  foregoing  manner,  and  will 
then  in  its  turn  propagate  its  kind  by  a  similar  process. 

32.  By  reasoning  upon  the  foregoing  history,  we  may  arrive  at  cer- 
tain conclusions,  which  will  be  found  equally  applicable  to  all  living 
beings.  In  the  first  place,  the  cell  originates  in  a  germ  or  reproduc- 
tive molecule,  which  has  been  prepared  by  another  similar  cell  that 


SCIENCE  OF  PHYSIOLOGY.  35 

previously  existed.  There  is  no  sufficient  reason  to  believe,  that 
there  is  any  exception  to  this  rule.  So  far  as  we  at  present  know, 
every  Plant  and  every  Animal  is  the  offspring  of  a  parent,  to  which 
it  bears  a  resemblance  in  all  essential  particulars;  and  the  same  may 
be  said  of  the  individual  cells,  of  which  the  Animal  and  Vegetable 
fabrics  are  composed.  But  how  does  this  germ^  this  apparently  homo- 
geneous molecule,  become  a  Cell  ?  The  answer  to  this  is  only  to  be 
found  in  its  peculiar  property  of  drawing  materials  to  itself  from  the 
elements  around,  and  of  incorporating  these  with  its  own  substance. 
The  Vegetable  cell  may  grow  wherever  it  can  obtain  a  supply  of 
Water  and  Carbonic  acid  ;  for  these  compounds  supply  it  with  Oxy- 
gen, Hydrogen,  and  Carbon,  in  the  state  most  adapted  for  the  exer- 
cise of  the  combining  power,  by  which  it  converts  them  into  that 
new  compound,  whose  properties  adapt  it  to  become  part  of  the 
growing  organized  fabric.  Here,  then,  we  have  two  distinct  opera- 
tions ; — the  union  of  the  Oxygen,  Hydrogen  and  Carbon,  into  that 
gummy  or  starchy  product,  which  seems  to  be  the  immediate  ■pabulum 
of  the  Vegetable  tissues ; — and  the  incorporation  of  that  product  with 
the  substance  of  the  germ  itself. 

33.  The^r5^  of  these  changes  may  Z>e,  and  probably  ^5,  of  a  purely 
Chemical  nature  ;  and  analogous  cases  are  not  wanting,  in  the  pheno- 
mena of  Inorganic  Chemistry,  in  which  one  body,  a,  exerts  an  influ- 
ence upon  two  other  bodies,  b  and  c,  so  as  to  occasion  their  separa- 
tion or  their  union,  without  itself  undergoing  any  change.  Thus 
Platinum,  in  a  finely-divided  state,  will  cause  the  union  of  Oxygen 
and  Hydrogen  at  ordinary  temperatures;  and  finely-powdered  Glass 
will  do  the  same  at  the  temperature  of  572°.  This  kind  of  action  is 
called  Catalysis.  A  closer  resemblance,  perhaps,  is  presented  by  the 
act  oi  fermentation ;  in  which  a  new  arrangement  of  particles  takes 
place  in  a  certain  compound,  by  the  presence  of  another  body  which 
is  itself  undergoing  change,  but  which  does  not  communicate  any  of 
its  elements  to  the  new  products.  Thus,  if  a  small  portion  of  animal 
membrane,  in  a  certain  stage  of  decomposition,  be  placed  in  a  solu- 
tion of  sugar,  it  will  occasion  a  new  arrangement  of  its  elements, 
which  will  generate  two  new  products,  alcohol  and  carbonic  acid.  If 
the  decomposition  of  the  membrane  have  proceeded  further,  a  differ- 
ent product  w^ill  result;  for  instead  of  alcohol,  lactic  acid  will  be 
generated.  There  appears  no  improbability,  then,  in  the  idea,  that 
the  influence  exerted  by  the  germinal  molecule  is  of  an  analogous 
nature;  and  that  it  operates  upon  the  elements  of  the  surrounding 
water  and  carbonic  acid,  according  to  purely  Chemical  laws,  uniting 
the  Carbon  with  the  elements  of  Water,  and  setting  free  the  Oxygen. 
This  result  of  the  nutritive  operations  of  the  simple  cellular  plants 
may  be  easily  verified  experimentally,  by  exposing  the  green  scum, 
which  floats  upon  ponds,  ditches,  &c.,  and  which  consists  of  the 
cells  of  a  minute  Cryptogamic  Plant,  to  the  influence  of  light  and 
warmth  beneath  a  receiver;  it  is  found  that  oxygen  is  then  liberated, 
by  the  decomposition  of  the  carbonic  acid  contained  in  the  water. 


36  NATURE  AND  OBJECTS  OF  THE 

We  shall  presently  have  to  return  to  the  consideration  of  the  Chemi- 
cal phenomena  of  living  beings;  and  shall  pass  on,  therefore,  to  con- 
sider those  to  which  no  such  explanation  applies. 

34.  The  second  stage  in  the  nutritive  process  consists  in  the  appro- 
priation of  the  new  product  thus  generated  to  the  enlargement  of  the 
living  cell-structure; — a  phenomenon  obviously  distinct  from  the  pre- 
ceding. It  is  well  to  observe,  that  this  process,  which  constitutes  the 
act  of  organization,  may  be  clearly  distinguished  in  the  higher  Plants 
and  Animals,  as  consisting  of  two  stages ;  the  first  of  these  being  the 
further  preparation  or  elaboration  of  the  fluid  matter,  by  certain  altera- 
tions whose  nature  is  not  yet  clear,  so  as  to  render  it  organizable,  or 
fit  to  undergo  organization ;  the  second  being  the  act  of  organization 
itself,  or  the  conversion  of  the  organizable  matter  into  the  solid  text- 
ure, and  the  development  in  it  of  the  properties  that  distinguish  that 
texture.  Thus,  for  example,  we  do  not  find  that  a  solution  of  dex- 
trin (or  starch-gurn)  is  capable  of  being  at  once  applied  to  the  deve- 
lopment of  vegetable  tissue,  although  it  is  identical  in  composition 
with  cellulose ;  for  it  must  first  pass  through  a  stage,  in  which  it  pos- 
sesses a  peculiar  glutinous  character,  and  exhibits  a  tendency  to  spon- 
taneous coagulation,  that  seems  like  an  attempt  at  the  production  of 
organic  forms.  And  in  like  manner  the  albumen  of  Animals  is  evi- 
dently not  capable  of  being  applied  to  the  nutrition  of  the  fabric,  until 
it  has  been  first  converted  into  fibrin ;  which  also  is  distinguished  by 
its  tenacious  character,  by  its  spontaneous  coagulability,  and  by  the 
fibrous  structure  of  the  clot.  Now,  in  both  these  cases,  there  is  pro- 
bably some  slight  modification  in  Chemical  composition,  that  is,  in 
the  proportions  of  the  ultimate  elements;  but  the  principal  alteration 
is  evidently  that  which  is  eflfected  by  the  re-arrangement  of  the  con- 
stituent particles;  so  that,  without  any  considerable  change  in  their 
proportions,  a  compound  of  a  very  diflferent  nature  is  generated.  Of 
the  possibility  of  such  changes,  we  have  abundant  illustrations  in 
ordinary  Chemical  phenomena ;  for  there  is  a  large  class  of  sub- 
stances, termed  isomeric,  which,  with  an  identical  composition,  pos- 
sess chemical  and  physical  properties  of  a  most  diverse  character. 

35.  But  we  cannot  attribute  the  production  of  Fibrin  from  Albu- 
men, the  organizable  from  the  unorganizable  material,  to  the  simple 
operation  of  the  same  agencies  as  those  which  determine  the  produc- 
tion of  the  different  isomeric  compounds;  for  the  properties  of  Fibrin 
are  much  more  vitally  distinct  from  those  of  Albumen,  than  they  are 
either  chemically  or  physically  ;  that  is,  we  find  in  the  one  an  inci- 
pient manifestation  of  Life,  of  which  the  other  shows  no  indications. 
The  spontaneous  coagulation  of  fibrin,  which  takes  place  very  soon 
after  it  has  been  withdrawn  from  the  vessels  of  the  living  body,  is  a 
phenomenon  to  which  nothing  analogous  can  be  found  elsewhere  ;  for 
it  has  been  clearly  shown  not  to  be  occasioned  by  any  mere  physical 
or  chemical  change  in  its  constitution  ;  and  it  takes  place  in  a  man- 
ner which  indicates  that  a  new  arrangement  of  particles  has  taken 
place  in  it,  preparatory  to  its  being  converted  into  a  living  solid.  For 


( 


SCIENCE  OF  PHYSIOLOGY.  37. 

this  coagulation  is  not  the  mere  homogeneous  settings  which  takes 
place  in  a  solution  of  gelatine  in  cooling,  nor  is  it  the  aggregation  of 
particles  in  a  mere  granular  state,  (closely  resembling  that  of  a  che- 
mical precipitate),  which  takes  place  in  the  coagulation  of  albumen: 
it  is  the  actual  production  of  a  sim^Xe  fibrous  tissue^  by  the  union  of 
the  particles  of  fibrin  in  a  determinate  manner,  bearing  a  close  resem- 
blance to  the  similar  process  in  the  living  body  (§  188).  We  say, 
then,  that  the  coagulation  of  Fibrin,  and  the  production  of  a  fibrous 
tissue,  are  the  result  of  its  vital  properties,  rather  than  of  chemical  or 
physical  agencies;  because  no  substance  is  known  to  perform  any 
such  actions,  without  having  been  subjected  to  the  influence  of  a  liv- 
ing body;  and  because  the  actions  themselves  are  altogether  different 
from  any  which  we  witness  elsewhere.  This  production  of  an  organ- 
izahle  or  partially  vitalized  substance,  from  an  unorganizable  one, 
possessing  none  but  chemical  properties,  and  therefore  as  yet  inert^ 
so  far  as  the  living  body  is  concerned,  may  be  termed  Assimilation  ; 
and  it  may  be  conceived,  as  we  have  seen,  to  consist  of  a  new 
arrangement  of  the  particles  of  the  substance  thus  changed,  analo- 
gous to  that  which  occurs  when  one  isomeric  product  is  converted 
into  another  by  some  ordinary  chemical  agency, — Heat  or  Electricity 
for  example ;  but  not  ideiitical  with  it,  because  it  cannot  be  produced 
by  any  other  agency  than  that  furnished  by  a  living  structure. 

36.  We  now  come  to  the  act  of  Organization  itself;  which  seems 
to  consist  of  a  continuation  of  the  same  kind  of  change, — that  is,  a 
new  arrangement  of  the  particles,  producing  substances  which  differ 
both  as  to  structure  and  properties  from  the  materials  employed,  but 
which  maybe  so  closely  allied  to  them  in  chemical  composition,  that 
the  difference  cannot  be  detected.  Thus,  from  the  dextrin  of  plants 
is  generated,  in  the  process  of  cell-development,  the  cellulose  which 
constitutes  the  walls  of  the  cells  :  chemically  speaking,  there  seems 
to  be  no  essential  distinction  between  these  two  substances  ;  and  yet 
between  the  living,  growing,  reproducing  cell,  and  the  inert,  un- 
changing starch-grain,  how  wide  the  difference  !  So  in  the  animal 
body,  we  find  that  the  composition  of  the  fibrin  of  muscular  fibre 
scarcely  differs,  in  regard  to  the  proportion  of  its  elements,  from  the 
fibrin,  or  even  from  the  albumen,  of  the  blood;  and  yet  what  an  en- 
tire re-arrangement  must  take  place  in  the  particles  of  either,  before 
a  tissue  so  complex  in  structure,  and  so  peculiar  in  properties,  as 
muscular  fibre,  can  be  generated! 

37.  Both  in  the  Plant  and  the  Animal,  we  find  that  tissues  present- 
ing great  diversities  both  in  structure  and  properties,  may  take  their 
origin  in  the  same  organizable  material ;  but  in  every  case  (at  least 
in  the  ordinary  processes  of  growth  and  separation)  the  new  tissue  of 
each  kind  is  formed  in  continuity  with  that  previously  existing.  Thus 
in  the  stem  of  a  growing  tree,  from  the  very  same  glutinous  sap  or 
cambium,  intervening  between  the  wood  and  the  bark,  the  wood  ge- 
nerates, in  contact  with  its  last-formed  layer,  a  new  cylinder  of  wood; 
whilst  the  bark  produces,  in  contact  with  its  last-formed  layer,  a  new. 


38  NATURE  AND  OBJECTS  OF  THE 

cylinder  of  bark, — the  woody  cylinder  being  characterized  by  the 
predominance  of  ligneous  fibre  and  ducts,  and  the  cortical  by  the 
predominance  of  cellular  tissue.  In  like  manner  we  find  that,  in 
animals,  muscle  produces  muscle,  bone  generates  bone,  nerve  deve- 
lops nerve  in  continuity  with  it, — all  at  the  expense  of  the  materials 
supplied  by  the  very  same  blood.  The  JVutrition  of  tissues,  by  the 
organization  of  the  materials  contained  in  the  nutrient  fluid  with 
which  they  are  supplied,  may  be  superficially  compared  therefore  to 
the  act  of  crystalization,  when  it  takes  place  in  a  mixed  solution  of 
two  or  more  salts.  If  in  such  a  solution  we  place  small  crystals 
of  the  salts  it  contains,  these  crystals  will  progressively  increase  by 
their  attraction  for  the  other  particles  of  the  same  kind,  which  were 
previously  dissolved  ;  each  crystal  attracting  the  particles  of  its  own 
salt,  and  exerting  no  influence  over  the  rest.  But  it  must  be  borne 
in  mind,  that  such  a  resemblance  goes  no  further  than  the  surface ; 
for  the  growth  of  a  crystal  cannot  be  really  regarded  as  in  the  least 
analogous  to  that  of  a  cell.  The  crystal  progressively  increases  by 
the  deposit  of  particles  upon  its  exterior ;  the  interior  undergoes  no 
change  ;  and  whatever  may  be  the  size  it  ultimately  attains,  its  pro- 
perties remain  precisely  the  same  as  those  of  the  original  nucleus. 
On  the  other  hand,  the  cell  grows  from  its  original  germ  by  a  pro- 
cess o{  interstitial  deposit;  the  substance  of  which  its  wall  is  composed, 
extends  itself  in  every  part ;  and  the  new  matter  is  completely  incor- 
porated with  the  old. 

38.  Moreover,  as  the  increase  proceeds,  we  see  an  evident  distinc- 
tion between  the  cell-wall  and  its  cavity ;  and  we  observe  that  the 
cavity  is  occupied  by  a  peculiar  matter,  different  from  the  substance 
of  the  cell- wall,  though  obviously  introduced  through  it.  Of  the 
essential  difference  which  may  exist  in  composition,  between  the 
cell-wall  and  the  contents  of  the  cavity,  we  have  a  remarkable  exam- 
ple in  the  case  of  the  simple  Cryptogamic  plant,  which  constitutes 
Yeast,  and  which  differs  in  no  essential  part  of  the  history  of  its  growth 
from  the  species  already  referred  to.  The  substance  of  its  cell-walls 
is  nearly  identical  with  ordinary  Cellulose ;  whilst  the  contents  of 
the  cells  are  closely  allied  in  composition  to  Protein,  the  material  of 
many  Animal  tissues.  Again,  in  the  fat-cells  of  Animals,  the  cell- 
wall  is  formed  from  a  protein  compound  ;  whilst  the  oily  contents 
agree,  in  the  absence  of  nitrogen,  and  in  their  general  chemical  rela- 
tions, with  the  materials  of  the  tissues  of  Plants.  It  is  evident,  then, 
that  one  of  the  inherent  powers  of  the  cell,  is  that  by  which  it  not  only 
combines  the  surrounding  materials  into  a  substance  adapted  for  the 
extension  of  its  wall^  but  that  which  enables  it  to  exercise  a  similar 
combining  power  on  other  materials  derived  from  the  same  source, 
and  to  form  a  compound, — of  an  entirely  different  character,  it  may 
be, — which  occupies  its  cavity.  Now  this  process  is  as  essential  to 
our  idea  of  a  living  cell,  as  is  the  growth  of  its  wall  ;  and  it  must 
never  be  left  out  of  view,  when  considering  the  history  of  its  deve- 
lopment. 


SCIENCE  OF  PHYSIOLOGY,  3^ 

39.  Every  kind  of  cell  has  its  own  specific  endowments ;  and  ge- 
nerates in  its  interior  a  compound  peculiar  to  itself.  The  nature  of 
this  compound  is  much  less  dependent  upon  the  nutrient  materials 
which  are  supplied  to  the  cell,  than  upon  the  original  inherent  powers 
of  the  cell  itself,  derived  from  its  germ.  Thus  we  find  that  the  Red 
Snow  and  Gory  Dew  invariably  form  a  peculiar  red  secretion  ;  and 
that  they  will  only  grow  where  they  can  obtain,  from  the  air  and 
moisture  around,  the  elements  of  that  secretion.  Again,  the  Yeast 
Plant  invariably  forms  a  secretion  analogous  to  animal  protein ;  and 
it  will  only  grow  in  a  fluid  which  supplies  it  with  the  materials  of 
that  substance.  Hence  the  Red  Snow  would  not  grow  in  a  ferment- 
ible  saccharine  fluid  ;  nor  would  the  Yeast  Plant  vegetate  on  damp 
cold  surfaces.  Yet  there  is  little  diff*erence,  if  any,  between  their  cell- 
walls  in  regard  to  chemical  composition. — So,  also,  we  shall  find 
hereafter,  that  one  set  of  cells  in  the  animal  body  will  draw  into 
themselves,  during  the  process  of  growth,  the  elements  of  bile  ;  ano- 
ther, the  elements  of  milk ;  another,  fatty  matter,  and  so  on  ; — the 
peculiar  endowments  of  each  being  derived  from  their  several  germs, 
which  seem  to  have  an  attraction  for  these  substances  respectively, 
and  which  thus  draw  them  together ;  whilst  the  cell-wall  appears  to 
have  a  uniform  composition  in  all  instances. 

40.  The  term  Secretion,  or  setting-apart,  is  commonly  applied  to 
this  operation,  to  distinguish  it  from  Nutrition  or  growth  ;  but  it  is 
obvious  from  what  has  now  been  stated,  that  the  act  of  secretion  is 
in  reality  the  increase  or  growth  of  the  cell-contents,  just  as  the  pro- 
cess of  enlargement  is  the  increase  or  growth  of  the  cell-wall ;  and 
that  the  tw^o  together  make  up  the  whole  process  of  Nutrition,  which 
cannot  be  properly  understood,  unless  both  are  taken  into  account. 
It  is  to  be  remembered,  however,  that  the  contents  of  the  cell  may 
not  be  destined  to  undergo  organization  ;  indeed  we  shall  find  here- 
after, that  the  main  use  of  certain  cells  is  to  draw  off  from  the  circu- 
lating fluid  such  materials  as  are  incapable  of  organization  ;  and  the 
operation  may  be  so  far  attributed,  therefore,  to  the  agency  of  Che- 
mical forces.  But  we  shall  find  that,  in  other  instances,  the  cell-con- 
tents are  destined  to  undergo  organization,  and  this  either  within  the 
parent-cell,  or  after  they  leave  it ;  here,  then,  we  must  recognize  a 
distinct  vitalizing  agency,  as  exerted  by  the  cell  upon  its  contents. 

41.  This  organizing  or  vitalizing  influence  must  be  exerted  upon 
a  certain  portion  of  the  contents  of  every  cell  that  is  capable  of  repro- 
ducing itself;  for  it  is  in  this  manner  that  those  germs  are  produced, 
in  which  all  the  wonderful  properties  are  inherent,  that  are  destined 
to  manifest  themselves,  when  they  are  set  free  from  the  parent-cell. 
This  power  of  Reproduction  is  one  of  those,  which  most  remarkably 
distinguishes  the  living  being ;  and  we  shall  find  that,  in  the  highest 
Animal,  as  in  the  humblest  Plant,  it  essentially  consists  in  the  prepa- 
ration of  a  cell-germ,  which,  when  set  free,  gradually  develops  itself 
into  a  structure  like  that  from  which  it  sprang.  The  reproductive 
molecules  or  cell-germs  are  formed,  like  the  tissue  and  the  contents 


40  NATURE  AND  OBJECTS  OF  THE 

of  the  parent-cell,  from  the  nutrient  materials  which  it  has  the  power 
of  bringing  together  and  combining ;  and  in  their  turn  they  pass 
through  a  corresponding  series  of  changes ;  and  at  length  produce  a 
new  generation  of  similar  molecules,  by  which  the  race  is  destined 
to  be  continued.  Notwithstanding  the  mystery  which  has  been  sup- 
posed to  attach  itself  to  this  process,  it  is  obvious  that  there  is  nothing 
in  reality  more  difficult  to  understand  in  the  fact  that  the  parent-cell 
organizes  and  vitalizes  the  cellulose  which  it  has  elaborated,  so  that 
it  should  form  the  germ  of  a  new  individual  possessing  similar  pro- 
perties with  itself,  than  in  its  incorporating  the  same  material  with 
its  own  structure,  and  causing  it  to  take  a  share  in  its  own  actions. 

42.  Finally,  the  parent-cell  having  arrived  at  its  full  development, 
having  passed  through  the  whole  series  of  changes  which  is  charac- 
teristic of  the  species,  and  having  prepared  the  germs  by  which  the 
race  is  to  be  propagated,  dies  and  decays; — that  is,  all  those  opera- 
tions, which  distinguish  living  organized  structures  from  inert  matter, 
cease  to  be  performed  ;  and  it  is  subject  to  the  influence  of  chemical 
forces  only,  which  speedily  occasion  a  separation  of  its  elements,  and 
cause  them  to  return  to  their  original  forms,  namely,  water  and  car- 
bonic acid.  It  must  not  be  hence  supposed,  however,  that  there  is 
anything  peculiar  in  the  forces  which  hold  together  those  elements 
during  the  life  of  the  cell,  and  that  the  operation  of  the  ordinary  che- 
mical agencies  is  resisted  by  the  superior  power  of  vitality.  On  the 
contrary  it  is  certain  that  interstitial  death  and  decay  are  incessantly 
taking  place  during  the  whole  life  of  the  being ;  and  that  the  main- 
tenance of  its  healthy  or  normal  condition  depends  upon  the  constant 
removal  of  the  products  of  that  decay,  and  upon  their  continual  re- 
placement. If,  on  the  one  hand,  those  products  be  retained,  they  act 
in  the  manner  of  poisons  ;  being  quite  as  injurious  to  the  welfare  of 
the  body,  as  the  most  deleterious  substances  introduced  from  without. 
On  the  other  hand,  if  they  be  duly  carried  off,  but  be  not  replaced, 
the  conditions  essential  to  vital  action  are  not  fulfilled,  and  the  death 
of  the  whole  must  be  the  result. 

43.  Now  it  is  to  be  observed  that,  as  Plants  obtain  the  materials 
oi  ih^u  growth  from  water  and  carbonic  acid,  taking  the  carbon  from 
the  latter  and  setting  free  the  oxygen,  so  do  they  require,  as  the  con- 
dition for  their  decay,  the  presence  of  oxygen,  which  may  unite  with 
the  carbon  that  is  to  be  given  back  to  the  atmosphere.  If  secluded 
from  this,  the  vegetable  tissues  may  be  preserved  for  a  long  time 
without  decomposition.  Generally  speaking,  indeed,  they  are  not 
prone  to  rapid  decay,  except  at  a  high  temperature  ;  and  hence  it  is 
that  we  have  so  little  evidence,  in  Plants,  of  the  constant  interstitial 
change,  of  which  mention  has  just  been  made.  Its  existence,  how- 
ever, (at  least  in  all  the  softer  portions  of  the  structure,)  is  made  evi- 
dent by  the  fact,  that  a  continual  extrication  of  carbonic  acid  takes 
place,  to  an  amount  which  sometimes  nearly  equals  that  of  the  car- 
bonic acid  decomposed,  and  of  the  oxygen  set  free,  in  the  act  of 
Nutrition  (§  33).     The   latter  operation  is  only  effected  under  the 


I 


SCIENCE  OF  PHYSIOLOGY.  41 

stimulus  of  sun-light ;  the  former  is  constantly  going  on,  by  day  and 
by  night,  in  sunshine  and  in  shade ;  and  if  it  be  impeded  or  prevented 
by  want  of  a  due  supply  of  oxygen,  the  plant  speedily  becomes  un- 
healthy. Now  this  extrication  of  the  products  of  interstitial  decay  is 
termed  Excretion.  It  is  usually  confined  in  Plants  to  the  formation 
of  carbonic  acid  and  water,  by  the  union  of  the  particles  of  their  tis- 
sues with  the  oxygen  of  the  air, — a  process  identical  with  that  which 
occurs  after  the  death  of  the  entire  structure.  But  in  Animals  it  is 
much  more  complicated,  owing  to  the  larger  number  of  constituents 
in  their  fabric,  and  to  the  much  greater  variety  in  the  proportions  in 
which  these  are  combined ;  hence  the  products  of  interstitial  decom- 
position are  much  more  numerous  and  varied,  and  several  distinct 
modes  are  devised  for  getting  rid  of  them.  Moreover,  as  the  animal 
tissues  are  much  further  removed  than  the  Vegetable  from  the  com- 
position of  Inorganic  bodies,  they  are  subject  to  much  more  rapid 
and  constant  decay;  and  we  shall  find  that  this  decay  is  so  consider- 
able in  amount,  as  to  require  on  the  one  hand  a  very  complex  excre- 
tory apparatus  to  carry  off  the  disintegrated  matter,  and  on  the  other 
a  large  supply  of  nutrient  material  to  replace  it. 

44.  The  preceding  history  may  be  thus  summed  up. — 1.  The  Vege- 
table cell-germ  or  reproductive  molecule  draws  to  itself,  and  combines 
together,  certain  inorganic  elements;  and  thereby  produces  a  new  and 
peculiar  compound.  This  compound,  however,  exhibits  no  properties 
that  distinguish  it  from  others,  in  which  ordinary  Chemical  agencies 
have  been  concerned ;  and  we  may,  therefore,  regard  the  first  act  of 
the  cell-germ  as  of  a  purely  chemical  nature.  We  shall  presently  see 
that  chemical  agencies  are  undoubtedly  concerned  in  it,  to  a  very  con- 
siderable degree.  The  Animal  cell-germ  does  not  possess  the  same 
Chemical  power ;  it  is  not  capable  of  decomposing  the  water,  carbonic 
acid,  and  ammonia,  which  include  the  elements  of  its  tissues ;  and  it  is 
entirely  dependent  for  its  growth  upon  the  supply  of  nutriment  pre- 
viously prepared  for  it  by  the  agency  of  the  vegetable  kingdom,  many 
species  of  which  possess,  as  we  have  seen,  the  power  of  generating  a 
protein  compound  within  their  cells,  though  they  cannot  organize  it. — 

2.  The  cell-germ  then  exerts  an  agency  upon  the  pabulum  thus  pre- 
pared ;  by  which  a  new  arrangement  of  its  particles  is  produced. 
This  new  arrangement  gives  new  and  peculiar  qualities  to  the  fluid, 
which  show  that  it  is  something  more  than  a  mere  chemical  compound, 
and  that  it  is  in  the  act  of  undergoing  the  process  of  organization. — 

3.  The  Organization  of  this  elaborated  pabulum  then  takes  place: 
its  materials  are  withdrawn  from  the  fluid,  and  incorporated  with  the 
solid  texture ;  and  in  thus  becoming  part  of  the  organized  fabric,  they 
are  caused  to  exhibit  its  own  peculiar  properties. — 4.  At  the  same 
time  another  portion  of  this  pabulum  is  gradually  prepared  to  serve  as 
the  germ  of  a  new  cell,  or  set  of  cells,  by  which  the  same  properties 
are  to  be  exhibited  in  another  generation. — 5.  By  a  Chemical  opera- 
tion resembling  that  concerned  in  the  first  preparation  of  the  pabulum, 
a  certain  secretion  more  or  less  differing  from  it  in  character,  but  not 


42  NATURE  AND  OBJECTS  OF  THE 

destined  to  undergo  organization,  is  formed  in  the  cavity  of  the  cell. — 
6.  A  decomposition  or  disintegration  of  the  organized  structure,  is 
continually  going  on,  by  the  separation  of  its  elements  into  simpler 
forms,  under  the  influence  of  purely  Chemical  agencies;  and  the  setting 
free  of  these  products  by  an  act  of  excretion,  is  thus  incessantly 
restoring  to  the  inorganic  world  a  portion  of  the  elements  that  have 
been  withdrawn  from  it. — 7.  When  the  term  of  life  of  the  parent- 
cell  has  expired,  and  its  reproductive  molecules  are  prepared  to  con- 
tinue the  race,  the  actions  of  nutrition  cease;  those  of  decomposition 
go  on  unchecked ;  and  the  death  of  the  structure,  or  the  loss  of  its 
distinguishing  vital  properties,  is  the  result.  By  the  decomposition, 
which  then  takes  place  with  increased  rapidity,  its  elements  are  re- 
stored to  the  inorganic  w^orld;  presenting  the  very  same  properties  as 
they  did  when  first  withdrawn  from  it;  and  becoming  capable  of  be- 
ing again  employed,  by  any  successive  numbers  of  living  beings,  to 
go  through  the  same  series  of  operations. 

45.  Thus,  then,  we  see  that  our  fundamental  idea  of  the  properties 
of  the  simplest  living  being  consists  in  this : — that  it  has  the  capability 
of  drawing  into  its  own  substance  certain  of  the  elements  furnished  by 
the  inorganic  w^orld ; — that  it  forms  these  into  new  combinations 
(which  the  Chemist  may  find  out  methods  of  imitating); — that  it  re- 
arranges the  particles  of  these  combinations,  in  that  peculiar  mode 
which  we  call  organization; — that  in  producing  this  new  arrangement 
it  also  calls  forth  or  develops  in  them  a  new  set  of  properties,  which 
we  call  vital,  and  which  are  manifested  by  them,  either  as  connected 
with  the  parent  structure,  or  as  appertaining  to  the  germs  of  new 
structures,  according  to  the  mode  in  which  the  materials  are  applied ; 
— that,  notwithstanding  its  peculiar  condition,  it  remains  subject  to 
the  ordinary  laws  of  Chemistry,  and  that  decomposition  of  its  struc- 
ture is  continually  taking  place ; — and  finally,  that  the  duration  of  its 
vital  activity  is  limited  ;  the  changes  which  the  organic  structure  un- 
dergoes, in  exhibiting  its  peculiar  actions,  being  such  as  to  render  it 
(after  a  longer  or  shorter  continuance  of  them)  incapable  of  any  longer 
performing  them. 

46.  There  is  abundant  evidence,  that  the  duration  of  the  Life^  or 
state  of  Vital  Jlctivity^  of  an  organized  structure,  is  inversely  propor- 
tioned to  the  degree  of  that  activity ;  and  consequently  that  Life  is 
shortened  by  an  increased  or  abnormal  activity;  -whilst  it  may  often 
be  prolonged  by  influences  which  diminish  that  activity.  Thus  we 
shall  hereafter  find  reason  to  believe,  that  the  duration  of  life  in  the 
Muscular  and  Nervous  tissues  of  Animals  is  entirely  dependent  upon 
the  degree  in  which  they  are  exercised  ;  every  call  upon  their  activity 
causing  the  death  and  disintegration  of  a  certain  part;  whilst  if  they 
be  allowed  to  remain  in  repose  for  a  time,  only  that  amount  of  decom- 
position will  take  place  to  which  their  chemical  character  renders  them 
liable.  Again,  we  may  trace  the  connection  between  the  vital  activ- 
ity of  a  part  and  the  duration  of  its  life,  by  comparing  the  transitory 
existence  of  the  leaves  of  a  Plant,  which  are  its  active  organs  of  nu- 


SCIENCE  OF  PHYSIOLOGY.  43 

trition  with  the  comparative  permanence  of  its  woody  stem^  the  parts 
of  which,  when  once  completely  formed,  undergo  very  little  subse- 
quent change.  The  most  striking  manifestation  of  this  connection, 
however,  is  afforded  by  that  condition  in  which,  without  any  appre- 
ciable amount  of  vital  activity  or  change,  an  organized  structure  may 
remain  unaltered  for  centuries  ;  not  only  presenting  at  the  end  of  that 
time  its  original  structure,  but  being  prepared  to  go  through  its  regular 
series  of  vital  operations,  as  if  these  had  never  been  interrupted. 
This  state  may  be  designated  as  Dormant  Vitality.  It  differs,  on  the 
one  hand,  from  Life;  because  life  is  a  state  of  Jidivity.  On  the  other 
hand,  it  differs  from  Death;  because  Death  implies  not  merely  a  sus- 
pension of  activity,  but  a  total  loss  of  vital  properties.  Now  in  the 
state  of  Dormant  vitality,  the  vital  properties  are  retained ;  but  they 
are  prevented  from  manifesting  themselves  by  the  want  of  the  neces- 
sary conditions.  When  these  conditions  are  supplied,  the  state  of 
vital  activity  is  resumed,  and  all  the  functions  of  life  go  on  with 
energy. 

47.  Of  this  Dormant  Vitality  it  may  be  well  to  adduce  some  ex- 
amples ;  which  may  assist  in  impressing  on  the  mind  of  the  student 
the  general  views  here  put  forth.  This  condition  is  manifested  in  the 
most  remarkable  manner  by  the  seeds  and  germs  of  plants :  many  of 
which  are  adapted  to  remain,  for  an  unlimited  period,  in  a  state  of 
perfect  repose,  and  yet  to  vegetate  with  the  greatest  activity,  as  soon 
as  ever  they  are  subjected  to  the  necessary  influence.  Thus  the 
sporules  of  the  Fungi,  which  can  only  germinate  in  decaying  organ- 
ized matter,  seem  universally  diffused  through  the  atmosphere,  and 
ready  to  vegetate  with  the  most  extraordinary  rapidity,  whenever  a 
fitting  opportunity  presents  itself.  This  at  least  appears  to  be  the 
only  feasible  mode  of  explaining  their  appearance,  in  the  forms  of 
Mould,  Mildew,  &c.,  on  all  moist  decaying  substances;  and  that  there 
is  no  improbability  in  the  supposition  itself,  is  shown  by  the  excessive 
multiplication  of  these  germs,  a  single  individual  producing  not  less 
than  ten  millions  of  them,  so  minute  as  when  collected  to  be  scarcely 
visible  to  the  naked  eye,  rather  resembling  thin  smoke,  and  so  light 
as  to  be  wafted  by  every  movement  of  the  atmosphere  ; — so  that,  in 
fact,  it  is  difficult  to  imagine  any  place  from  which  they  can  be  ex- 
cluded. Moreover  it  is  certain  that  an  equally  tenacious  vitality  exists 
in  the  seeds  of  higher  plants.  Those  of  most  species  inhabiting  tempe- 
rate climates  are  adapted  to  remain  dormant  during  the  winter;  and 
may  be  easily  preserved,  in  dry  air,  and  at  a  moderate  temperature, 
for  many  years.  Some  of  those  which  had  been  kept  in  the  Herba- 
rium of  Tournefort  during  upwards  of  a  century,  were  found  to  have 
preserved  their  fertility.  Cases  are  of  no  unfrequent  occurrence,  in 
which  ground  that  has  been  turned  up,  spontaneously  produces  plants 
dissimilar  to  any  in  their  neighbourhood.  There  is  no  doubt  that  in 
some  of  these  cases,  the  seed  is  conveyed  by  the  wind,  and  becomes 
developed  in  spots  which  afford  congenial  soil, — as  already  remarked 
in  the  case  of  the  Fungi.     Thus  it  is  commonly  observed  that  clover 


44  NATURE  AND  OBJECTS  OF  THE 

makes  its  appearance  on  soils  which  have  been  rendered  alkaline  by 
lime,  by  strewed  wood-ashes,  or  by  the  burning  of  weeds.  But  there 
are  many  authentic  facts,  which  can  only  be  explained  upon  the  sup- 
'^josition,  that  the  seeds  of  the  newly-appearing  plants  have  lain  for  a 
long  period  imbedded  in  the  soil,  at  such  a  distance  from  the  surface 
as  to  prevent  the  access  of  air  and  moisture  ;  and  that,  retaining  their 
vitality  under  these  circumstances,  they  have  been  excited  to  germi- 
nation when  at  last  exposed  to  the  requisite  conditions.  Thus  Pro- 
fessor Lindley  states  as  a  fact,  that  he  has  raised  three  raspberry-plants 
from  seeds  taken  from  the  stomach  of  a  man,  whose  skeleton  was  found 
thirty  feet  below  the  surface  of  the  earth,  at  the  bottom  of  a  barrow 
which  was  opened  near  Dorchester ;  as  his  body  had  been  buried 
with  some  coins  of  the  Emperor  Hadrian,  there  could  be  no  doubt 
that  the  seeds  were  1600  or  I'TOO  years  old.  Again,  there  are  un- 
doubted instances  of  the  germination  of  grains  of  wheat,  which  were 
inclosed  in  the  wrappers  of  Egyptian  mummies,  perhaps  twice  that 
number  of  years  ago ;  the  wheat  being  different  in  some  of  its  charac- 
ters from  that  now  growing  in  the  country. 

48.  These  facts  make  it  evident,  that  there  is  really  no  limit  to  the 
duration  of  this  condition ;  and  that  when  a  seed  has  been  thus  pre- 
served for  ten  years,  it  may  be  for  a  hundred,  a  thousand,  or  ten 
thousand, — provided  no  change  of  circumstances  either  exposes  it  to 
decay,  or  calls  its  vital  properties  into  activity.  Hence  in  cases  where 
seeds  have  been  buried  deep  in  the  earth,  not  by  human  agency,  but 
by  some  geological  change,  it  is  impossible  to  say  how  long  anteriorly 
to  the  creation  of  man  they  may  have  been  produced  and  buried, — 
as  in  the  following  very  curious  instance.  Some  well-diggers  in  a 
town  on  the  Penobscot  river,  in  the  State  of  Maine  (New  England), 
about  forty  miles  from  the  sea,  came  at  the  depth  of  about  twenty  feet 
upon  a  stratum  of  sand,  which  strongly  excited  curiosity  and  interest, 
from  the  circumstance  that  no  similar  sand  was  to  be  found  anywhere 
in  the  neighbourhood,  and  that  none  like  it  was  nearer  than  the  sea- 
beach.  As  it  was  drawn  up  from  the  well,  it  was  placed  in  a  pile  by 
itself;  an  unwillingness  having  been  felt  to  mix  it  with  the  stones  and 
gravel  which  were  also  drawn  up.  But  when  the  work  was  about  to 
be  finished,  and  the  pile  of  stones  and  gravel  to  be  removed,  it  was 
necessary  also  to  remove  the  sand-heap.  This,  therefore,  was  scat- 
tered about  the  spot  on  which  it  had  been  formed,  and  was  for  some 
time  scarcely  remembered.  In  a  year  or  two,  however,  it  was  per- 
ceived that  a  large  number  of  small  trees  had  sprung  from  the  ground 
over  which  the  heap  of  sand  had  been  strewn.  These  trees  became 
in  their  turn  objects  of  strong  interest,  and  care  was  taken  that  no 
injury  should  come  to  them.  At  length  it  was  ascertained  that  they 
were  Beach-Plum  trees  ;  and  they  actually  bore  the  Beach-Plum, 
which  had  never  before  been  seen,  except  immediately  upon  the  sea- 
shore. The  trees  had  therefore  sprung  from  seeds,  which  were  in  the 
stratum  of  sea-sand,  that  had  been  pierced  by  the  well-diggers.  By 
what  convulsion  they  had  been  thrown  there,  or  how  long  they  had 


SCIENCE  OF  PHYSIOLOGY.  45 

quietly  slept  beneath  the  surface,  cannot  possibly  be  determined  with 
exactness ;  but  the  enormous  length  of  time  that  must  have  elapsed, 
since  the  stratum  in  which  the  seeds  were  buried  formed  part  of  the 
sea-shore,  is  evident  from  the  accumulation  of  no  less  than  twenty 
feet  of  vegetable  mould  upon  it. 

49.  Numerous  instances  will  be  related  in  the  succeeding  Chapter, 
of  the  occurrence  of  a  similar  condition  in  fully-developed  Plants,  and 
even  in  animals  of  high  organization.  In  some  of  these  it  is  a  regular 
part  of  the  history  of  their  lives,  coming  on  periodically  like  sleep ; 
whilst  in  others  it  is  capable  of  being  induced  at  any  time,  by  a 
withdrawal  of  some  of  the  conditions  essential  to  vital  activity.  In 
regard  to  all  of  them,  however,  it  may  be  observed,  that  the  vitality 
can  only  be  retained,  w^hen  the  organized  structure  itself  is  secluded 
from  such  influences  as  would  produce  its  decay.  Thus  the  hard  dry 
tissue  of  the  seed  is  but  little  liable  to  decomposition  ;  and  all  that  is 
usually  required  for  the  prevention  of  change  in  its  structure,  is  seclu- 
sion from  the  free  access  of  air  and  from  moisture,  and  a  steady  low 
or  moderate  temperature.  If  a  seed  be  exposed  to  air  and  moisture, 
but  the  temperature  be  not  high  enough  to  occasion  its  germination, 
it  will  gradually  undergo  decay,  and  will  consequently  lose  its  vitality. 
The  animal  tissues  are  more  liable,  as  already  mentioned,  to  sponta- 
neous decomposition ;  and  the  only  instances  in  which  they  can  retain 
their  vitality  for  a  lengthened  period,  without  any  nutritive  actions, 
are  those  in  which  all  decomposition  is  prevented,  either  by  the  action 
of  cold,  or  by  the  complete  deprivation  of  air  or  of  moisture — as 
when  Frogs,  Snakes,  &c.,  have  been  preserved  for  years  in  an  ice- 
house, or  Wheel-Animalcules  have  been  dried  upon  a  slip  of  glass. 

50.  The  class  of  phenomena  last  brought  under  notice,  serves  to 
exhibit  in  a  very  remarkable  manner  the  dependence  of  all  Vital 
Action,  upon  certain  other  conditions,  than  those  furnished  by  the 
organized  structure  possessed  of  vital  properties.  Thus  a  seed  does 
not  germinate  of  itself ;  it  requires  the  influence  of  certain  external 
agents,  such  as  warmth, — air,  and  moisture  ;  and  it  can  no  more  pro- 
duce a  plant  without  the  operation  of  these,  than  warmth,  air,  and 
moisture  could  produce  it  of  themselves.  Hence  these  agents  supply 
a  set  of  conditions  which  are  equally  essential  to  vital  action,  with 
the  properties  of  the  organized  structure  itself;  and  as  they  excite 
those  properties,  or  call  them  into  activity,  they  are  termed  Vital 
Stimuli.  Now^  we  have  in  this  fact  a  complete  analogy  with  the 
phenomena  which  we  may  elsewhere  notice.  Thus,  as  already 
pointed  out,  the  property  of  mutual  attractiveness  between  masses  of 
matter  is  only  manifested,  when  more  than  one  mass  is  present ;  and 
unless  that  condition  be  supplied,  the  property  remains  dormant.  Or, 
again,  the  attractive  property  of  a  magnet  is  only  manifested,  when  a 
piece  of  iron  is  brought  into  its  proximity.  We  find  still  closer  ana- 
logies in  the  phenomena  of  Chemistry  ;  thus  there  are  many  chemical 
operations,  which  require  a  certain  amount  of  heat  as  a  necessary 
condition  ;  and  the  heat  may  be  justly  said  to  be  the  stimulus  to  the 


46  NATURE  AND  OBJECTS  OF  THE 

chanpje.  We  find,  indeed,  that  the  amount  of  heat  is  even  capable  of 
subversing  the  relative  affinities  of  two  bodies  for  a  third  ;  and  that 
thus  two  changes  of  an  opposite  character  may  be  induced  by  the 
simple  regulation  of  temperature.  For  example,  at  a  white  heat,  the 
affinity  of  iron  for  oxygen  is  so  much  stronger  than  that  of  potassium, 
that,  by  placing  iron  in  contact  with  potassa,  the  latter  is  decomposed, 
and  the  result  is  oxide  of  iron  and  potassium.  At  ordinary  tempera- 
tures, on  the  other  hand,  the  affinity  of  potassium  for  oxygen  is  much 
the  stronger  of  the  two ;  and  if  potassium  and  oxide  of  iron  be  then 
brought  to  act  upon  each  other,  the  oxygen  quits  the  latter,  and 
restores  the  former  to  the  condition  of  potassa.  Hence  we  may 
justly  say,  that  a  particular  temperature  is  the  stimulus  to  each  of 
these  actions.  In  the  same  manner,  the  influence  of  light  is  con- 
cerned in  producing  a  large  number  of  chemical  changes,  including 
all  those  which  are  concerned  in  the  formation  of  Photographic  pictures 
of  various  kinds ;  the  materials  concerned  in  these  changes  remain 
dormant  or  inactive,  so  long  as  they  are  not  subjected  to  its  influence  ; 
but  when  it  is  allow^ed  to  operate  upon  them,  it  gives  occasion  to 
acts  of  decomposition  and  new  combination,  to  which  acts  it  may  be 
properly  said  to  be  the  stimulus. 

51.  Hence  the  dependence  of  Vital  actions  upon  certain  external 
stimuli,  as  well  as  upon  the  properties  of  the  organism  w^hich  manifest 
them,  is  no  greater  than  the  dependence  of  any  of  the  phenomena, 
exhibited  by  an  inorganic  substance,  upon  some  other  agency  external 
to  itself.  In  fact,  no  change  whatever  can  he  said  to  be  truly  sponta- 
neous; that  is,  no  property  can  manifest  itself,  unless  it  be  called  into 
action  by  some  stimulus  fitted  to  excite  it.  Thus  when  spontaneous 
decomposition  (as  it  is  commonly  termed)  occurs  in  an  organized  or 
inorganic  substance,  it  is  due  to  the  forces  generated  by  the  mutual 
attraction  between  certain  elements  of  the  substance,  and  the  oxygen 
of  the  atmosphere  ;  and  this  attraction  is  sufficient  to  overcome  the 
attraction,  which  tends  to  hold  together  the  particles  in  their  original 
state.  If  the  air  be  totally  excluded,  decay  will  not  take  place  ;* 
because  no  new  force  comes  into  operation,  to  cause  a  separation  of 
the  components  from  their  original  modes  of  union.  The  influence 
of  the  Vital  Stimuli, — that  is,  the  conditions  in  regard  to  Heat,  Light, 
&c.,  which  are  essential  to  Vital  activity, — will  be  fully  explained  in 
the  next  Chapter ;  and  at  present  it  will  be  sufficient  to  remark,  that 
the  degree  in  which  they  are  supplied  possesses  a  well-marked 
influence  upon  the  amount  of  activity  and  energy  manifested  in  the 
actions  of  the  organized  structure ;  that  there  is  a  limitation  in  the 
case  of  each  of  them,  as  to  the  degree  in  which  it  can  operate  bene- 
ficially, the  limitation  being  usually  narrower  and  more  precise,  accord- 
ing to  the  elevation  of  the  being  in  the  scale  ;  that  an  excessive  supply 

*  On  this  principle,  meats,  vegetables,  and  even  liquid  sonps,  are  now  largely  pre- 
served, for  the  use  of  persons  undertaking  long  voyages;  by  enclosing  them  in  tia 
cases,  carefully  soldered  up.  There  is  no  limit  to  the  time,  during  which  decompo- 
sition may  thus  be  prevented. 


SCIENCE  OF  PHYSIOLOGY.  47 

may  be  destructive  to  the  vital  properties  of  the  structure,  by  over- 
stimulating  it  and  thus  causing  it  to  live  too  fast,  or  by  more  directly 
producing  some  physical  or  chemical  change  in  its  condition  ;  and  that 
a  deficiency  will  keep  down  or  suspend  all  vital  activity,  leaving  the 
structure  to  the  unrestrained  operation  of  those  agents  which  are 
always  tending  to  its  disintegration,  and  consequently  occasioning  a 
speedy  loss  of  the  vital  properties, — save  in  those  cases  in  which  they 
may  be  preserved  in  a  dormant  condition,  and  which  are  exceptions 
to  the  general  rule,  that  the  death  or  departure  of  the  vital  properties 
follows  closely  upon  the  cessation  of  vital  actions. 

52.  Our  fundamental  idea  of  Life^  then,  is  that  of  a  state  of  con- 
stant change  or  action ;  this  change  being  manifested  in  at  least  two 
sets  of  operations ; — the  continual  withdrawal  of  certain  elements  from 
the  inorganic  world ; — and  the  incorporation  of  these  with  the  peculiar 
structures  termed  organized,  or  the  production  from  them  of  the  germs 
that  are  hereafter  to  accomplish  this.  As  the  conditions  of  this  con- 
tinual change,  we  recognize  the  necessity  of  an  organized  structure 
on  the  one  hand,  or  of  a  germ  which  is  capable  of  becoming  so; 
whilst  we  also  perceive  the  necessity  of  a  supply  of  certain  kinds  of 
matter  from  the  inorganic  world,  capable  of  being  combined  into  the 
materials  of  that  structure,  which  may  be  designated  as  the  alimentary 
substances;  and,  further,  we  see  that  the  organism  can  exert  no  influ- 
ence upon  these,  except  with  the  assistance  of  certain  other  agencies, 
such  as  light,  heat,  &c.,  which  are  termed  vital  stimuli.  This  ex- 
pression includes  all  the  essential  phenomena  of  vegetative  or  organic 
life  ;  whether  as  witnessed  in  the  lowest  or  highest  members  of  the 
Vegetable  kingdom ;  or  as  displayed  in  a  large  proportion  of  the 
structures  composing  the  Animal  fabric. 

53.  But  just  as  we  find  among  Inorganic  bodies,  that  various 
kinds  are  to  be  distinguished  by  their  different  properties,  whilst  all 
agree  in  the  general  or  essential  properties  of  matter,  so  do  we  find 
that  living  organized  substances  are  distinguished  by  a  variety  of  pro- 
perties inherent  in  themselves,  whilst  they  all  agree  in  the  foregoing 
general  or  essential  characters.  In  many  instances,  the  difference  of 
their  properties  is  as  obviously  coincident  with  differences  in  their 
structure  and  composition,  as  it  usually  is  among  the  bodies  of  the 
Mineral  world :  thus  we  always  find  the  property  of  Contractility  on 
the  application  of  a  stimulus,  restricted  to  a  certain  form  of  organized 
tissue,  the  Muscular ;  and  we  find  that  the  property  by  which  that 
stimulus  is  capable  of  being  generated  and  conveyed  to  a  distance,  is 
restricted  to  another  kind  of  tissue,  the  Nervous.  In  a  great  number 
of  cases,  however,  very  obvious  differences  in  properties  manifest 
themselves,  when  no  perceptible  variations  exist,  either  in  structure  or 
composition ;  thus  it  would  be  impossible  to  distinguish  the  germ-cell 
of  a  Zoophyte  from  that  of  Man,  by  any  difference  in  its  aspect  or 
composition  ;  yet  neither  can  be  developed  into  any  other  form  than 
that  of  the  parent  species,  and  they  must  be  regarded,  therefore,  as 
essentially  different  in  properties.     In  the  same  manner  we  shall  find 


48  CONNECTION  BETWEEN  VITALITY  AND  ORGANIZATION. 

that,  in  the  same  organized  fabric,  there  are  very  great  varieties  in  the 
actions  of  its  component  cells,  which  indicate  a  similar  variety  in 
their  properties  ;  and  yet  they  are  to  all  appearance  identical.  But 
there  can  be  no  reasonable  doubt,  that  differences  really  exist  in  such 
cases ;  though  our  means  of  observation  are  not  such  as  to  enable  us 
to  take  cognizance  of  these,  by  the  direct  impressions  they  make  upon 
our  senses.  Analogous  instances  are  not  wanting  in  the  Mineral 
world  ;  for  the  Chemist  is  familiar  with  a  class  of  compounds  de- 
signated isomorphous,  in  w^hich,  with  perfect  similarity  in  external 
form  and  physical  properties,  there  is  a  difference,  more  or  less  com- 
plete, in  chemical  composition. 

54.  Whatever  may  be  the  peculiar  vital  properties  possessed  by  an 
organized  tissue,  we  find  that  they  are  always  dependent  upon  the 
maintenance  of  its  characteristic  structure  and  composition,  by  the 
nutritive  operations  of  which  we  have  spoken ;  and  that  they  thus 
form  a  part,  as  it  were,  of  the  more  general  phenomena  of  its  Life. 
They  manifest  themselves  with  the  first  complete  development  of  the 
tissue  ;  they  are  retained  and  exhibited  so  long  as  active  nutritive 
changes  are  taking  place  in  it;  their  manifestation  is  weakened  or 
suspended  if  the  nutritive  operations  be  feebly  exerted;  and  they  de- 
part altogether,  whenever,  by  the  cessation  of  those  actions,  and  the 
uncompensated  influence  of  ordinary  Chemical  forces,  the  structure 
begins  to  lose  that  normal  composition  and  arrangement  of  parts, 
which  constitutes  its  state  of  organization.  Hence  we  may  regard 
these  peculiar  properties  as  conformable,  in  all  the  essential  condi- 
tions of  their  existence,  with  those  more  general  properties,  which 
have  been  previously  dwelt  upon  as  characterizing  a  living  organized 
structure. 

3.   Connection  between  Vitality  and  Organization. 

55.  The  idea  that  new  properties  may  be  called  forth  or  developed 
by  a  new  combination  of  elements,  and  by  a  new  arrangement  of  par- 
ticles,— and  that,  consequently,  the  class  of  properties  included  under 
the  general  term  vital  is  dependent  upon  the  peculiar  state  of  matter 
which  is  designated  as  organized, — is  so  perfectly  conformable  to 
what  is  seen  elsewhere,  and  is  so  fully  sufficient  to  explain  all  ob- 
served phenomena,  that  it  would  scarcely  seem  necessary  to  use  any 
further  argument  in  support  of  it.  But  the  notion  has  been  enter- 
tained, that  Vitality  is  a  something  superadded  to  matter,  and  that  it 
is  absurd  to  suppose  that  the  phenomena  of  Life  can  be  produced  by 
any  combinations  of  matter  ;  and  this  indeed  so  generally  prevails, 
that  it  seems  desirable  to  carry  our  investigations  with  regard  to  the 
causes  of  Vital  phenomena  a  little  further. 

56.  We  have  seen  that  the  properties  of  any  kind  of  matter,  even 
those  with  which  we  are  most  familiar,  require  certain  conditions  for 
their  manifestation.  Even  the  properties  of  which  we  take  most 
direct  cognizance  by  our  senses,  do  not  manifest  themselves  to  us, 


CONNECTION  BETWEEN  VITALITY  AND  ORGANIZATION.  49 

until  they  have  made  a  change  in  the  condition  of  our  own  organs.  And 
in  regard  to  those,  which  require  a  stimulus  of  some  kind  to  call  them 
into  action,  our  acquaintance  with  them  entirely  depends  upon  whether 
the  conditions  of  their  action  have  been  afforded.  Thus,  to  go  back 
to  a  former  illustration,  supposing  a  new  chemical  element  to  be  dis- 
covered, we  could  not  know  its  properties  in  regard  to  heat,  electri- 
city, or  magnetism,  the  mode  of  its  combination  with  other  elements, 
the  nature  and  properties  of  the  compounds  produced,  their  reactions 
with  other  compounds,  &c.  &c.,  until  we  have  tried  a  complete  series 
of  experiments  upon  it, — that  is,  until  we  have  placed  it  in  all  the 
circumstances  or  conditions  requisite  to  manifest  the  properties,  with 
which  we  seek  to  become  acquainted,  or  whose  absence  we  seek  to 
determine  if  they  do  not  exist.  Now  we  might  have  made  all  the 
experiments  we  could  devise  upon  such  a  body ;  and  yet  we  might 
have  failed  in  detecting  some  remarkable  and  distinguishing  property 
inherent  in  it,  simply  because  w^e  had  not  placed  it  in  the  requisite 
circumstances  for  the  manifestation  of  this  peculiarity.  Further,  even 
in  the  elements  or  compounds  with  w^hich  we  are  best  acquainted,  it 
is  very  possible  that  properties  exist,  of  which  we  as  yet  know  no- 
thing, simply  because  they  have  not  yet  been  called  into  action  by 
the  requisite  combination  of  conditions.  For  example,  no  one  would 
have  thought  it  possible,  a  few  years  since,  that  water  could  be  frozen 
in  a  red-hot  metallic  vessel ;  and  yet  this  is  now  know^n  to  be  effected 
with  ease  and  certainty,  in  the  proper  combination  of  conditions. 

57.  Again,  it  is  by  no  means  a  sufficient  definition  of  one  of  these 
elements, — Oxygen,  for  example, — to  enumerate  its  properties  in  its 
simple  or  uncombined  state  ;  these  are  the  properties  of  oxygen  gas ; 
but  a  complete  enumeration  of  the  properties  of  oxygen  itself  w^ould 
include  a  reference  to  those  of  every  compound  substance  into  which 
it  enters,  as  well  as  to  the  conditions  under  which  they  manifest  them- 
selves. We  are  accustomed  to  think  of  the  properties  of  these  com- 
pounds, as  if  they  were  something  altogether  distinct  from  those  of 
the  elements  of  which  they  are  composed ;  thus  in  considering  the 
properties  of  water,  we  commonly  lose  sight  of  the  fact,  that  it  is 
formed  by  the  union  of  oxygen  and  hydrogen,  and  that  we  must  re- 
gard these  elements  as  possessing,  in  a  dormant  state,  the  capability 
of  manifesting  such  properties,  when  they  are  brought  together  under 
certain  conditions.  Yet  we  cannot  reason  upon  the  ordinary  opera- 
tions of  Chemistry,  without  coming  to  the  conclusion?^  that  the  very 
act  of  combination  calls  forth  or  develops  properties,  which  were 
pre-existent  in  the  components,  and  which  became  manifest  as  soon 
as  these  were  placed  in  the  circumstances  required  to  display  them. 

58.  It  must  not  be  forgotten,  that  the  properties  of  a  compound 
substance  are,  in  general  at  least,  altogether  different  from  those  which 
present  themselves  in  either  of  its  components  ;  so  that  we  could  not 
in  the  least  degree  judge  of  the  former  from  the  latter,  or  of  the  latter 
from  the  former.  What  more  different,  for  example,  from  the  physi- 
cal and  chemical  properties  of  Water,  from  those  of  either  the  Oxygen 

4 


50         CONNECTION  BETWEEN  VITALITY  AND  ORGANIZATION. 

or  the  Hydrogen  that  enter  into  its  composition  ?  Or  what  more  dif- 
ferent than  the  properties  of  a  neutral  salt,  from  those  of  the  acid  and 
alkali  by  whose  union  it  is  produced  ?  We  are  continually  witness- 
ing, then,  the  complete  change  effected  in  the  sensible  properties  of 
bodies,  by  acts  of  combination  or  separation  ;  these  acts  calling  forth 
or  developing  properties  that  were  previously  dormant,  and  reducing 
to  the  dormant  condition  those  which  were  previously  sensible.  That 
this  is  the  true  way  of  accounting  for  the  phenomena  would  appear 
from  the  fact,  that  in  all  cases  the  converse  change  brings  back  the 
original  properties  ;  thus  the  oxygen  and  hydrogen  resulting  from  the 
decomposition  of  water,  have  all  the  properties  of  oxygen  and  hy- 
drogen that  are  being  combined  into  water.  Their  properties,  then, 
have  undergone  no  real  change ;  the  ostensible  change  being  due  to 
the  development  of  some  of  the  properties  of  the  elements,  and  the 
reduction  of  others  to  the  dormant  state,  by  the  very  alteration  of 
their  conditions. — Even  a  change  in  the  condition  of  a  single  body, 
without  any  combination,  may  cause  new  properties  to  be  manifested 
by  it,  and  old  ones  to  become  dormant.  Thus  the  particles  of  water 
have  so  strong  an  attraction  for  each  other,  at  a  low  temperature,  as 
to  become  aggregated  in  a  crystaline  form,  and  to  produce  a  dense 
solid  mass  ;  at  somewhat  a  higher  temperature,  their  mutual  attraction 
is  so  slight,  that  a  very  small  amount  of  mechanical  force  is  sufficient 
to  separate  them,  and  they  move  upon  each  other  with  the  utmost 
freedom  ;  whilst  at  a  still  higher  temperature,  they  manifest  a  power 
of  mutual  repulsion,  which  increases  with  the  greatest  rapidity  with 
every  augmentation  of  temperature.  Yet  when  the  temperature  of 
the  substance  is  lowered  to  its  former  standards,  we  observe  that  it 
first  returns  to  the  liquid,  and  then  to  the  solid  form ;  and  that,  in 
those  states,  it  manifests  all  the  properties  which  before  characterized 
it, 

59.  Again,  not  merely  the  physical,  but  the  chemical  properties  of 
bodies  may  be  affected  by  a  change  in  their  mechanical  condition. 
Thus,  it  is  well  known  that  oxygen  and  iron,  at  ordinary  tempera- 
tures, have  a  mutual  affinity,  which  is  only  sufficient  to  produce  a 
slow  combination  between  them  ;  whilst  at  high  temperatures,  that 
affinity  is  such  as  to  cause  their  rapid  and  energetic  union.  Now  if 
iron,  in  a  state  of  very  minute  division, — such  as  it  possesses  when 
set  free  from  the  state  of  oxide  by  means  of  hydrogen,  at  the  lowest 
possible  temperature, — be  brought  into  contact  with  oxygen  or  even 
with  atmospheric  air,  at  ordinary  temperatures,  it  immediately  be- 
comes red-hot,  and  is  converted  into  an  oxide.  The  minuteness  of 
the  division,  predisposing  to  chemical  union,  appears  to  be  the  occa- 
sion of  our  power  of  causing  many  substances  to  combine,  when  one 
or  both  are  in  the  nascent  state  (that  is,  when  just  set  free  from  some 
other  combination),  which  could  not  be  made  to  unite  in  any  more 
direct  manner ;  thus,  when  a  quantity  of  any  preparation  of  Arsenic, 
however  minute,  is  dissolved  in  fluid  in  which  hydrogen  is  being 
generated,  the  hydrogen  will  detach  the  m^etal  from  its  previous  com- 


I 


CONNECTION  BETWEEN  VITALITY  AND  ORGANIZATION.  51 

bination,  and  will  pass  forth  in  union  with  it,  as  arseniuretted  hydro- 
gen,— a  compound  which  cannot  be  formed  by  the  direct  union  of 
the  elements.  In  like  manner,  in  that  mechanical  mixture  of  three 
finely-divided  substances,  which  we  call  Gunpowder,  the  rapidity 
with  which  combustion  is  propagated  through  the  largest  collection 
of  it,  is  entirely  dependent  upon  the  minute  subdivision  of  its  com- 
ponents, and  the  very  close  approximation  of  their  particles.  Hence 
it  may  be  very  correctly  said,  that  the  true  chemical  properties  of  the 
substances  are  not  manifested,  except  when  they  are  in  a  state  of  very 
minute  division ;  and  that  these  are  in  fact  obscured,  by  the  aggrega- 
tion of  the  particles  into  masses. 

60.  Thus,  then,  we  are  at  no  loss  to  discover  examples,  in  the 
Inorganic  world,  of  an  interchange  of  the  sensible  properties,  both 
Chemical  and  Physical,  of  the  bodies  composing  it,  by  a  change  in 
the  conditions  in  which  they  are  placed.  And  it  may  be  stated  as  a 
general  fact,  that  we  never  witness  the  manifestation  of  new  proper- 
ties in  a  substance,  unless  it  has  undergone  some  change  in  its  own 
condition,  of  which  altered  state  these  properties  are  the  necessary 
attendants.  We  have  no  right,  therefore,  to  speak  of  any  property  as 
distinct  horn  the  matter  which  exhibits  it;  or  as  capable  of  being 
superadded  to  it,  or  subtracted  from  it.  On  the  other  hand  we  are  led 
to  the  conception  oi properties  as  either  dormant  or  latent^  on  the  one 
hand;  or  as  active  or  sensible  on  the  other;  the  difference  being 
entirely  due  to  the  condition  of  the  substance.  Thus,  oxygen  and 
hydrogen  have  a  latent  or  dormant  affinity  for  each  other ;  this  does 
not  manifest  itself  in  either  of  them,  so  long  as  they  are  separate;  nor 
does  it  manifest  itself  at  ordinary  temperatures,  when  they  are  min- 
gled together.  But  if  through  such  a  mixture  we  transmit  an  electric 
spark,  or  if  we  raise  the  temperature  of  the  smallest  part  of  it  by  the 
contact  of  a  heated  body,  or  if  we  simply  introduce  into  it  a  portion 
of  platinum  in  a  state  of  minute  division,  the  requisite  stimulus  or 
excitation  is  given  to  these  affinities,  and  chemical  union  of  the  two 
substances  is  the  result. 

61.  Now  if  we  apply  these  views  to  the  phenomena  of  Life  and 
Organization,  we  see  that  they  enable  us  to  regard  these  phenomena 
as  analogous  in  character  to  those  of  the  Inorganic  world,  though  not 
identical  with  them  ;  and  they  lead  to  a  simplification  of  our  ideas  of 
them,  which  more  clearly  marks  out  the  path  to  be  pursued  in  their 
investigation.  We  find  that  the  essential  materials  of  Animal  and 
Vegetable  structures  are  the  four  elements.  Oxygen,  Hydrogen,  Car- 
bon, and  Nitrogen ;  these  are  distinguished  by  the  extraordinary 
number  and  variety  of  the  combinations  into  which  they  will  enter, — 
so  much  so,  indeed,  as  to  constitute,  in  this  respect,  a  group  quite 
distinct  from  all  the  other  elementary  substances.  Now  we  are  per- 
fectly justified  by  what  we  elsewhere  see,  in  attributing  to  these  ele- 
ments the  property  or  dormant  capability  of  exhibiting  vital  actions 
(in  addition  to  the  ordinary  chemical  ones  with  which  we  are  fami- 
liar), so  soon  as  they  are  placed  in  the  requisite  conditions;  in  other 


52         CONNECTION  BETWEEN  VITALITY  AND  ORGANISATION. 

words,  as  soon  as  they  are  made  a  part  of  the  living  system  by  the 
process  of  Organization.  It  is  only  the  peculiarity  of  the  conditions 
required  to  manifest  this  capability,  which  prevents  us  from  recogniz- 
ing it  as  an  ordinary  property  of  matter,  or  at  least  of  those  forms 
of  it,  which  we  know  by  experience  to  be  capable  of  entering  into 
organized  structures. 

62.  Thus  we  perceive,  that  Vital  properties  are  called  forth  or  de- 
veloped in  the  substance  of  the  germ,  whilst  this  substance  is  being 
organized  by  the  agency  of  its  parent;  these  vital  properties  are  such 
as  to  give  it  the  means  of  assimilating  and  organizing  the  materials 
supplied  by  the  inorganic  world,  and  whilst  thus  making  them  a  part 
of  its  own  structure,  to  cause  them  to  manifest  their  vital  properties ; 
and  these  are  exercised  in  their  turn,  in  making  further  additions  to 
the  growing  structure,  and  in  the  formation  of  the  reproductive  germ. 
In  this  germ  we  cannot  perceive  a  single  trace  of  the  future  being ; 
the  various  organs  and  structures  of  which  are  evolved  by  a  process 
of  subsequent  development.  And  it  is  probable  that,  in  the  complete 
organism,  not  a  single  particle  remains  of  those  which  originally  con- 
stituted its  germ.  Now  it  seems  absurd  to  suppose  that  in  a  single 
cell- germ,  a  molecule  almost  invisible  with  a  high  magnifying  power, 
a  force  is  concentrated,  which  is  afterwards  to  be  diffused  through  the 
whole  structure  of  a  vast  tree;  or  through  the  ever-changing  fabric  of 
a  complex  animal ;  and  which  is  not  only  to  animate  the  individual 
organism,  but  is  to  occasion  the  production  of  thousands  or  tens  of 
thousands  of  germs,  each  possessing  a  similar  force,  and  capable  of 
imparting  it  to  their  successors.  On  the  other  hand,  if  we  suppose 
that  the  germ  calls  forth,  or  excites,  the  dormant  properties  of  the 
combining  elements  (like  the  spongy  platinum,  or  the  electric  spark, 
in  a  mixture  of  oxygen  and  hydrogen), — that  it  thus  originates,  first 
a  chemical  combination,  and  then  a  peculiar  structural  arrangement, 
— that  in  consequence  of  this  new  combination  and  arrangement,  the 
elements  then  manifest  peculiar  properties  in  place  of  their  old  ones, 
which  last  as  long  as  they  exist  in  that  condition, — that,  when  their 
union  in  the  organized  fabric  is  dissolved,  they  lose  these  newly- 
manifested  properties,  return  to  their  original  form,  and  manifest 
precisely  the  same  properties  as  before  they  were  combined, — and 
that  they  are  capable  of  being  thus  operated  on,  time  after  time,  their 
properties  not  being  added  to,  or  lost,  but  those  which  were  latent 
being  developed,  and  those  which  were  at  first  sensible  becoming 
latent, — we  get  rid  of  every  difficulty,  at  the  same  time  that  we  reason 
in  accordance  with  the  fundamental  principles  of  Logic  and  Philoso- 
phy, which  forbid  us  to  assume  any  agency  that  is  not  requisite  to 
explain  the  phenomena. 

63.  The  elements.  Oxygen,  Hydrogen,  Carbon  and  Nitrogen,  in 
a  certain  state  of  combination  and  arrangement,  form  the  substance 
which  we  term  Muscular  fibre ;  and  they  then  manifest  certain  pecu- 
liar properties,  which  we  designate  as  vital.  On  the  other  hand, 
those  same  elements  exist  in  nearly  the  same  proportions,  but  in  a 


CONNECTION  BETWEEN  VITALITY  AND  ORGANIZATION.  53 

different  state  of  combination  and  arrangement,  in  the  substance 
which  we  term  Cyanate  of  Ammonia ;  and  they  then  exhibit  a  differ- 
ent set  of  properties,  which  we  call  Physical  and  Chemical.  Now 
we  have  just  as  much  right  to  say,  that  the  contractility  of  muscular 
fibre  results  from  the  peculiar  combination  and  arrangement  of  the 
elementary  particles  in  its  substance,  as  we  have  to  say  that  the  solidi- 
ty, translucency,  hardness,  and  other  qualities  of  the  salt  (all  of  which 
are  opposed  to  the  vital  properties,  and  cannot  co-exist  with  them), 
are  necessarily  connected  with  its  peculiar  mode  of  combination  and 
crystaline  aggregation.  If  we  were  acquainted  with  these  elements 
only  as  they  exist  in  organic  compounds,  their  transposition  into  a 
crystaline  salt  would  be  almost  as  marvelous  to  us,  as  the  opposite 
change  is  now. 

64.  The  general  history  of  the  Phenomena  of  Life  is  fully  conform- 
able with  the  view,  that  the  Vital  properties  of  a  tissue  are  dependent 
upon  that  state  of  combination  and  arrangement  which  is  termed 
Organization.  As  long  as  each  tissue  retains  its  normal  or  regular 
constitution,  renovated  by  the  actions  of  absorption  and  deposition 
through  which  that  constitution  is  preserved,  and  surrounded  by  those 
other  conditions  which  a  living  system  alone  can  afford,  so  long,  we 
have  reason  to  believe,  it  will  retain  its  vital  properties, — and  no 
longer.  And  just  as  we  have  no  evidence  of  the  existence  of  vital 
properties  in  any  other  form  of  matter  than  that  which  we  call  organ- 
ized, so  have  we  no  reason  to  believe  that  organized  matter  can  re- 
tain its  regular  constitution,  and  be  subjected  to  its  appropriate 
stimuli,  without  exhibiting  vital  actions.  The  advance  of  pathological 
science  renders  it  every  day  more  probable  (indeed  the  probability 
may  now  be  said  to  amount  to  almost  positive  certainty),  that  de- 
rangement in  function, — in  other  words,  an  imperfect  or  irregular 
action, — always  results,  either  from  some  change  of  structure  or  com- 
position in  the  tissue  itself,  or  from  some  corresponding  change  in  the 
stimuli  by  which  the  properties  of  the  organ  are  called  into  action. 
Thus,  when  a  Muscle  has  been  long  disused,  it  can  scarcely  be  ex- 
cited to  contraction  by  the  usual  stimulus,  or  may  even  be  altogether 
powerless;  and  minute  examination  of  its  structure  shows  it  to  have 
undergone  a  change,  which  is  obvious  to  the  microscope,  though  it 
may  not  be  perceptible  to  the  unaided  eye,  and  which  results  from 
imperfect  nutrition.  Or,  again,  convulsive  or  irregular  actions  of  the 
Nervous  system  may  be  produced,  not  by  any  change  in  its  own  com- 
position, but  by  the  presence  of  various  stimulating  substances  in  the 
blood,  although  their  amount  be  so  small  that  they  can  scarcely  be 
recognized. 

65.  As  there  is  a  constant  tendency,  in  the  Animal  tissues  more 
especially,  to  spontaneous  decay,  so  must  the  maintenance  of  the  vital 
properties  depend  upon  their  continual  regeneration  by  the  nutritive 
operations.  Hence  we  have  no  difficulty  in  accounting  for  the  Death 
of  the  whole  system,  on  the  cessation  or  serious  disturbance  of  any  one 
important  function ;  for  any  such  check  or  change  must  suspend  or 


54  CONNECTION  BETWEEN  VITALITY  AND  ORGANIZATION. 

disorder  the  nutrient  processes,  in  such  a  degree  that  they  can  no 
longer  maintain  the  normal  constitution  of  the  several  tissues.  But 
as  there  is  a  great  variety  in  the  rapidity  of  the  decomposition  of  the 
tissues,  when  the  act  of  nutrition  is  suspended,  so  do  we  witness  a 
corresponding  variety  in  the  duration  of  their  vital  properties,  after 
that  permanent  severance  of  the  chain  of  functions,  which  is  distin- 
guished as  somatic  death, — i.  e.,  the  death  of  the  body  as  a  whole. 
It  is  by  the  Circulation  of  the  Blood,  that  the  connection  of  the  dif- 
ferent functions  is  essentially  maintained ;  that  fluid  being  not  only 
the  material  for  the  nutrition  of  the  tissues,  but  in  many  cases  serving 
also  as  the  stimulus  to  their  activity.  Hence  with  the  permanent 
cessation  of  the  Circulation,  5oma/ic  death  must  be  regarded  as  taking 
place. 

66.  Yet  after  this,  we  observe  that  vitality  lingers  in  the  tissues; 
and  that  it  departs  from  them  only  as  they  lose  their  proper  composi- 
tion. Thus  we  find  that,  although  the  Nervous  centres  cannot  originate 
the  stimulus  necessary  to  produce  Muscular  contraction,  after  the  Cir- 
culation has  ceased, — yet  the  Nervous^6re5  can  convey  such  a  stimu- 
lus, long  after  somatic  death ;  so  that  contractions  may  be  excited  in 
muscles  by  the  application  of  galvanism,  or  of  mechanical  or  chemical 
stimulants,  to  the  trunks  that  supply  them.  The  molecular  death  of  the 
Nervous  tissue,  therefore,  has  not  yet  taken  place.  After  a  time,  how- 
ever, this  power  is  lost ;  the  tissue  no  longer  exhibits  its  distinguishing 
vital  properties ;  and  incipient  decomposition  and  change  of  structure 
manifest  themselves.  Yet  for  some  time  after  this,  the  Muscular 
tissue,  especially  in  a  cold-blooded  animal,  continues  to  possess  its 
peculiar  contractility ;  for  contractions  may  be  excited  in  it,  by  stimuli 
directly  applied  to  itself,  long  after  the  nerves  have  ceased  to  convey 
their  influence.  Sometimes,  indeed,  the  contractility  of  muscle  endures, 
until  changes  in  its  structure  and  composition  become  evident  to  the 
senses;  thus  the  heart  of  a  Sturgeon,  removed  from  the  body,  and  hung 
up  to  dry,  has  been  known  to  continue  alternately  contracting  and 
dilating,  until  the  movement  produced  a  crackling  noise,  in  conse- 
quence of  the  dryness  of  the  texture.  Again,  there  is  evidence,  that 
various  processes  of  nutrition  and  secretion  may  go  on,  for  some  time 
after  somatic  death,  and  even  after  the  removal  of  the  organs  from  the 
body,  provided  a  sufficient  quantity  of  blood  remains  in  them  ;  and  the 
blood  itself  retains  its  vitality,  so  as  not  to  coagulate,  whilst  contained 
in  the  vessels  of  tissues  still  living. 

67.  Hence  it  is,  that  parts  which  have  been  completely  separated 
from  the  body  may  often  be  reunited  with  it,  if  they  were  previously 
in  a  healthy  state,  and  too  much  time  has  not  elapsed  ;  thus,  there 
are  many  cases  on  record,  in  which  fingers,  toes,  noses,  or  ears,  that 
have  been  accidentally  chopped  off,  have  been  made  to  adhere  and 
grow  as  before,  by  bringing  the  cut  surfaces  into  contact,  even  some 
hours  after  their  severance.  It  is  evident,  then,  that  the  parts  so 
severed  cannot  have  lost  their  vitality;  since  no  treatment  could  pro- 
duce union  between  a  dead  mass  and  a  living  body.     And  we  are 


CONNECTION  BETWEEN  VITALITY  AND  ORGANIZATION.         55 

fully  justified  in  assuming  that,  in  cases  where  attempts  at  such  re- 
union have  not  been  successful,  the  death  of  the  separated  part  has 
resulted  from  the  too-prolonged  interruption  of  its  regular  nutritive 
operations,  whereby  chemical  and  physical  changes  have  taken  place 
in  it,  and  destroyed  the  peculiar  structure  and  composition  of  its 
several  parts.  The  ordinary  phenomena  of  Death,  therefore,  as  well 
as  those  of  Life,  bear  out  the  views  which  have  been  here  advanced. 

68.  But  it  has  been  maintained  by  those  who  consider  Vitality  as 
something  superadded  to  an  Organized  Structure,  essentially  independ- 
ent of  it,  and  capable  of  being  subtracted  from  it,  that  Death  fre- 
quently takes  place  under  circumstances,  which  leave  the  organism 
as  it  was  ;  so  that  "  the  dead  body  may  have  all  the  organization  it 
ever  had  whilst  alive."  For  such  an  assumption,  there  is  not  the 
least  foundsstion.  In  nearly  all  cases  in  which  death  takes  place  as 
a  result  of  disease,  the  connection  between  changes  of  structure  and 
composition,  either  in  the  tissues  or  in  the  blood,  and  such  a  loss  of 
the  vital  properties  of  some  part  or  organ  as  is  sufficient  to  bring  the 
Circulation  to  a  stand,  is  so  palpable  as  to  require  no  proof;  and  in 
by  far  the  greater  majority  of  cases  in  which  it  is  not  at  once  obvious, 
a  more  careful  scrutiny  will  reveal  it.  It  must  be  confessed  on  both 
sides,  that  our  means  of  investigation,  and  our  knowledge  of  the 
normal  structure  and  composition  of  the  tissues  and  the  blood,  are 
not  yet  sufficient  to  enable  us  to  detect  minute  shades  of  alteration, 
nor  to  assert  what  extent  of  change  is  inconsistent  with  the  continu- 
ance of  life.  And  as  no  one  has  yet  shown,  by  the  careful  and  exact 
microscopical  and  chemical  examination  of  the  solids  and  fluids  of  a 
dead  body,  that  it  has  all  the  organization  it  had  whilst  alive,  the 
assertion  above  quoted  is  totally  unwarranted  by  experience,  and  is 
contradicted  by  all  our  positive  knowledge  of  the  matter.  (See  § 
187.) 

69.  But  it  has  been  urged,  that  Death  may  result  from  the  sudden 
operation  of  some  agency  of  an  immaterial  character,  which  leaves 
no  trace  behind  it, — such  as  a  powerful  electric  shock,  or  a  violent 
mental  emotion.  Here,  too,  the  argument  entirely  fails.  It  is  impos- 
sible that  a  powerful  electric  shock  could  be  transmitted  through  a 
mass  like  the  animal  body,  composed  of  elements  in  such  a  loose 
state  of  combination  that  they  are  always  undergoing  decomposition, 
without  producing  important  chemical  changes  in  it ;  and  its  imper- 
fect conducting  power  renders  it  equally  liable  to  physical  disturb- 
ances. As  a  matter  of  fact  it  has  been  noticed,  that  the  bodies  of 
animals  killed  by  electricity  pass  into  decomposition  with  unusual 
rapidity ;  showing  that  the  ordinary  chemical  affinities  of  their  com- 
ponents have  received  a  powerful  stimulus;  and  it  has  also  been 
ascertained,  that  when  Eggs  in  process  of  development  have  had 
their  vitality  destroyed  by  an  Electric  shock,  the  minute  vessels  of 
the  vascular  area  (Chap.  XI.)  have  been  ruptured. — Nor  is  it  more 
difficult  to  explain  the  immediate  cause  of  death,  as  a  result  of  Men- 
tal emotion.     In   some  cases,  an  obvious  physical  change  has  been 


56  CONNECTION  BETWEEN  VITALITY  AND  ORGANIZATION. 

produced  by  the  too  violent  action  of  the  heart,  the  movements  of 
which  are  stimulated  by  the  emotion  ;  thus,  even  in  a  healthy  person, 
rupture  of  the  heart  or  aorta  has  been  known  to  take  place,  an  occur- 
rence to  which  those  affected  by  previous  disease  of  that  organ  are 
much  more  liable.  Where  there  is  any  disorder  in  the  heart's  action, 
resulting  from  thickened  valves,  narrowed  orifices,  &c.,  the  physical 
influence  of  mental  emotion  can  be  easily  accounted  for.  But  it 
must  be  admitted  that  cases  have  occurred,  in  which  no  such  explana- 
tion can  be  offered ;  sudden  death  having  taken  place  without  any 
perceptible  structural  cause.  We  are  not  obliged,  however,  to  have 
recourse  to  any  hypothesis  for  an  explanation  of  even  these  cases, 
which  is  not  borne  out  by  ample  analogy.  For  it  is  well  known  that 
mental  emotions  exert  a  powerful  influence  over  the  composition  of 
the  fluids  of  the  body,  and  are  capable  of  instantaneously  altering 
these.  Thus  in  many  human  beings,  and  still  more  in  the  lower 
animals,  alarm  or  agitation  will  occasion  the  immediate  disengage- 
ment of  powerfully  odorous  secretions,  which  must  have  resulted 
from  new  combinations  suddenly  formed.  And  there  can  be  no 
doubt  that  a  fit  of  passion  may  immediately  occasion  such  a  change 
in  the  milk  of  a  nurse,  as  renders  it  a  rank  poison  to  the  infant. 
There  is  no  reason  to  doubt,  therefore,  that  the  blood  itself  may 
undergo  changes  of  analogous  character  from  the  same  cause  ;  and 
that  it  may  become  a  violent  poison  to  the  individual  himself,  instead 
of  being  the  source  of  wholesome  nutriment,  or  the  stimulus  to  vital 
activity. 

70.  To  conclude,  then  ; — we  only  know  of  Vital  action^  as  exhi- 
bited by  an  Organized  structure,  under  the  influence  of  certain  stimuli; 
and  we  only  know  of  Vitality^  or  the  state  or  endowment  of  the  being 
that  exhibits  that  action,  as  conjoined  with  that  particular  aggregation 
and  composition  which  we  term  Organization.  The  real  cause  of 
that  endowment  must  be  traced  to  the  properties  of  the  original  ele- 
ments of  the  structure  exhibiting  it,  and  to  the  conditions  under 
which  they  came  into  action.  We  have  thus  two  objects  for  con- 
sideration, in  regard  to  the  process  of  organization  and  the  develop- 
ment of  the  vital  properties  ;  namely,  the  original  component  elements, 
and  the  organizing  germ  which  is  the  means  of  bringing  them  into 
combination.  The  former  are  permanent  in  their  character,  for  what- 
ever be  the  nature  of  the  changes  they  are  made  to  undergo,  in  the 
various  acts  of  combination,  they  manifest  their  original  properties 
when  restored  to  their  pristine  state,  and  can  thus  be  successfully 
made  to  form  part  of  innumerable  compounds,  organic  or  inorganic. 
On  the  other  hand,  the  properties  of  the  germ  are  but  transitory  ;  its 
own  existence,  as  well  as  the  duration  of  the  entire  organism  to  which 
it  gives  rise,  is  limited  ;  and  the  whole  Organized  Creation  would 
speedily  come  to  an  end,  and  would  be  resolved  into  its  pristine 
elements,  if  a  provision  had  not  been  made  in  the  reproductive  pro- 
cess, for  antagonizing  the  continual  decay  of  living  beings  by  a  con- 
tinual succession. 


CONNECTION  BETWEEN  VITALITY  AND  ORGANIZATION.  57 

71.  For  the  existence  of  those  dormant  properties  in  the  elements 
commonly  termed  inorganic,  which  enable  them  to  become  component 
parts  of  organized  structures  and  then  to  perform  vital  actions,  we  can 
assign  no  other  cause  than  the  Will  of  the  Creator.  The  constancy 
of  the  actions  which  result  from  them,  when  the  conditions  are  the 
same, — that  is,  their  conformity  to  a  fixed  plan,  or  (in  the  language 
commonly  employed)  their  subordination  to  laws^ — indicates  the  con- 
stancy and  unchangeableness  of  the  Divine  Will,  as  well  as  the  Infinity 
of  that  Wisdom,  by  which  the  plan  was  at  first  arranged  with  such 
perfection,  as  to  require  no  departure  from  it,  in  order  to  produce  the 
most  complete  harmony  in  its  results. 

72.  So  also,  if  we  endeavour  to  assign  a  cause  for  the  existence  of 
a  cell-germ,  we  are  led  at  first  to  fix  upon  the  vital  operations  of  the 
parerital  organism  by  which  it  was  produced.;  and  for  these  we  can 
assign  no  other  cause  than  the  peculiar  endowments  of  27^  components, 
brought  into  activity  by  the  cell-germ  that  originated  it.  Thus  we 
are  obliged  to  go  backw^ards  in  idea  from  one  generation  to  another  ; 
and  when  at  last  brought  to  a  stand  by  the  origin  of  the  race,  we  are 
obliged  to  rest  in  the  Divine  Will  as  the  source  of  those  wonderful 
properties,  by  which  the  first  germ  developed  the  first  organism  of  the 
race  from  materials  previously  unorganized,  this  organism  producing  a 
second  germ,  the  second  germ  a  second  organism,  and  so  on  without 
limit,  by  the  uniform  repetition  of  the  same  processes.  Yet  we  are 
not  to  suppose  that  the  continuation  of  the  race  is  really  in  any  way 
less  dependent  upon  the  Will  of  the  Creator,  than  the  origin  of  it. 
For  whilst  Science  leads  us  to  discard  the  idea  that  the  Deity  is  con- 
tinually interfering^  to  change  the  working  of  the  system  He  has  made, 
— since  it  everywhere  presents  us  with  the  idea  of  uniformity  in  the 
plan,  and  of  constancy  in  the  execution  of  it, — it  equally  discourages 
the  notion  entertained  by  some,  that  the  creation  of  matter,  endowed 
with  certain  properties,  and  therefore  subject  to  certain  actions,  was 
i\i&  final  act  of  the  Deity,  as  far  as  the  present  system  of  things  is  con- 
cerned, instead  of  being  the  mere  commencement  of  His  operations. 
If  it  be  admitted,  that  matter  owes  its  origin  and  properties  to  the 
Deity,  or,  in  other  words,  that  its  first  existence  vj^ls  but  an  expression 
of  the  Divine  Will,  what  is  its  continued  existence,  but  a  continued 
operation  of  that  same  Will  ?  To  suppose  that  it  could  continue  to 
exist,  and  to  perform  its  various  actions,  hy  itself,  is  at  once  to  assume 
the  property  of  self-existence  as  belonging  to  matter,  and  thus  to  do 
away  with  the  necessity  of  a  Creator  altogether ; — a  conclusion  to 
which  it  may  be  safely  aflSrmed  that  no  ordinarily-constituted  Man 
can  arrive,  who  reasons  upon  the  indications  of  Mind  in  the  pheno- 
mena of  Nature,  in  the  same  way  as  he  does  in  regard  to  the  creations 
of  Human  Art. 


58  VITAL  STIMULI. 


CHAPTER  II. 

OF  THE  VITAL  STIMULI. 

73.  It  has  been  shown  in  the  preceding  Chapter,  that  the  most 
general  conditions  of  Vital  phenomena  are  two-fold  ; — one  set  being 
supplied  by  the  organized  structure,  which  is  endowed  (in  virtue  of 
its  organization)  with  certain  peculiar  properties,  but  which  is  inert  so 
long  as  it  is  altogether  secluded  from  the  influence  of  external  agents ; 
— and  the  other  being  furnished  by  external  agents  of  various  descrip- 
tions, some  of  which  supply  the  materials  from  which  the  organized 
structure  is  built  up,  whilst  others  serve  to  stimulate  or  excite  the 
process  of  organization,  or  call  forth  the  peculiar  properties  of  the 
organized  structure.  Thus  in  the  case  of  the  germinating  seed,  the 
embryo  within,  possessed  of  a  peculiar  organization,  and  capable  of 
development  into  a  living  fabric  of  complex  structure,  remains  in  a 
dormant  state,  until  it  is  aroused  to  activity  by  the  influence  of  warmth, 
air,  and  moisture.  Here,  then,  we  have  the  distinction  between  the 
organism  and  the  external  agents  most  palpably  exhibited.  No  vital 
activity  can  manifest  itself  without  the  concurrence  of  both;  and  the 
germ  could  no  more  produce  a  plant  without  the  materials  supplied  to 
it  by  the  external  world,  and  the  stimuli  which  excite  it  to  the  action 
of  appropriating  these,  than  the  latter  could  develop  themselves  into 
a  plant,  without  the  formative  agency  of  the  germ. 

74.  In  this  dependence  of  Vital  action  upon  the  concurrence  of 
several  conditions,  we  only  see  that  which  is  true,  under  a  simpler 
form,  of  Chemical  action ;  and  here,  too,  we  trace  the  distinct  agency 
of  the  materials  employed,  and  the  stimuli  which  excite  their  mutual 
aflSnities,  and  thus  bring  about  their  union.  The  materials  of  Chemi- 
cal Action  are  the  substances  (either  elementary  or  composite),  which 
are  ready  to  enter  into  new  combinations  with  each  other ;  and  that 
readiness  or  Affinity  is  one  of  their  distinguishing  properties.  Thus 
the  mutual  affinities  of  oxygen  and  hydrogen,  or  of  an  acid  and  an 
alkali,  are  characteristic  properties  of  these  substances  respectively. 
Sometimes  this  affinity  is  strong  enough  to  cause  union  between  the 
substances  under  any  ordinary  circumstances.  But  in  many  other 
cases,  a  stimulus  of  some  kind  is  necessary  to  bring  these  aflinities  to 
bear  (so  to  speak)  upon  one  another.  Now  the  stimuli  to  Chemical 
action  belong  to  the  class  of  agents  commonly  termed  imponderable^ — 
namely.  Light,  Heat,  and  Electricity;  and  the  union  between  two 
substances,  which  were  previously  altogether  dormant  in  regard  to 
each  other,  although  in  close  contact,  may  be  frequently  caused  to  take 
place,  wath  various  manifestations  of  energy,  by  the  momentary  influ- 
ence of  one  of  these  agents.     Thus,  when  chlorine  and  hydrogen  are 


VITAL  STIMULI.  59 

mingled  together  in  a  bottle,  and  this  is  placed  in  darkness,  they  may 
be  kept  for  any  length  of  time  without  change  ;  but  if  they  are  exposed 
to  diffused  daylight,  they  slowly  Unite  ;  and  if  they  be  subjected  to 
the  direct  rays  of  the  sun,  instantaneous  explosion  takes  place,  with 
production  of  hydrochloric  acid.  Here,  then,  the  agency  of  Light 
brings  the  previously-dormant  affinities  of  these  two  bodies  into  a  state 
of  activity  in  regard  to  each  other.  The  same  effect  may  be  produced 
by  Heat ;  for  a  union  of  the  two  gases,  with  a  violent  explosion,  takes 
place  when  any  incandescent  substance  is  introduced  into  the  mixture. 
And  a  like  result  is  produced  hy  Electricity ;  hydrochloric  acid  being 
generated  under  the  same  circumstances,  by  the  influence  of  the 
electric  spark. "* 

75.  In  like  manner  it  is  requisite  to  distinguish,  among  the  external 
agents  that  concur  with  the  organic  germ  to  produce  an  organized 
structure,  between  those  which  furnish  the  materials  of  that  structure, 
or  which  enter  into  chemical  union  with  its  elements,  and  those  which 
act  as  stimuli  to  its  actions ;  and  we  find  that  this  distinction  coincides, 
as  in  the  former  case,  with  the  division  between  the  ponderable  or 
material,  and  the  imponderable  agents.  Under  the  former  group  are 
included  the  various  elements,  which  are  capable  of  being  appro- 
priated by  the  organism  as  the  materials  of  its  own  structure,  and 
which  are  possessed  of  peculiar  propAies  that  are  then  developed  ; 
in  other  words,  the  various  articles  of  food.  The  oxygen  of  the 
atmosphere,  whose  union  with  certain  elements  of  the  organism,  in 
the  process  of  Respiration,  is  also  an  agent  essential  to  its  functional 
activity, — belongs  to  the  same  division.  The  general  dependence  of 
the  living  organized  body  upon  food  and  oxygen,  has  been,  however, 
already  noticed  ;  and  it  will  be  preferable  to  defer  the  detailed  con- 
sideration of  the  mode  and  conditions  under  which  they  act  upon  it, 
until  the  history  of  the  Nutritive  operations  is  more  fully  entered  upon. 
This  will  be  the  fitting  opportunity,  however,  for  the  examination  of 
the  general  influence  of  the  Imponderable  agents,  and  of  some  others 
which  cannot  be  so  well  treated  of  elsewhere. 

76.  In  regard  to  all  these  Vital  Stimuli  it  may  be  observed,  that 
the  dependence  of  Vital  Action  upon  their  constaiit  influence  is  greater 
in  proportion  to  the  high  organization  of  their  structure,  and  vice  versa; 
so  that  beings  of  simple  organization  are  capable  of  enduring  a  depri- 
vation of  these  stimuli,  which  would  be  fatal  to  those  higher  in  the 
scale.  This  will  be  partly  understood,  when  it  is  borne  in  mind  that 
the  higher  the  development  of  the  living  being,  the  more  complete  is 
the  distribution  of  its  different  actions  amongst  separate  organs, — the 
more  close,  therefore,  is  their  mutual  dependence, — and  the  more 
readily,  in  consequence,  are  they  all  brought  to  a  close  by  the  inter- 

*  Although  the  conditions  of  this  union  appear  linDited  to  the  mutual  proximity  of 
the  two  bodies,  and  to  the  influence  of  one  of  these  three  stimuli,  yet  it  may  be  asserted 
that  they  are  probably  more  complex  than  they  appear;  for  although  a  high  tempera- 
ture is  competent  to  produce  their  union  when  Heat  is  employed  alone,  yet  it  is  pro- 
bable that  neither  Light  nor  Electricity  would  suffice  to  effect  it,  if  they  were  Dot  kepi 
in  the  gaseous  state  by  the  large  amount  o{  latent  heat  they  possess. 


60  VITAL  STIMULI. 

ruption  of  any  one.  But  there  is  no  doubt,  that  the  actions  of  even 
the  individual  parts  of  the  higher  organisms  require  for  their  excite- 
ment a  greater  supply  of  these  stimuli,  than  the  similar  actions  of  the 
corresponding  parts  in  the  lower :  whilst  if  these  stimuli  be  exerted 
upon  the  lower  with  the  intensity  that  is  required  for  the  higher,  they 
destroy  the  vital  properties  of  the  tissues  altogether,  by  the  excess  of 
their  action.  This  distinction  is  most  obvious  in  regard  to  the  rela- 
tive influence  of  Heat,  upon  warm-blooded  and  cold-blooded  animals; 
of  which  examples  will  be  given  hereafter. 

77.  It  may  also  be  observed  of  the  influence  of  these,  as  of  that  of 
other  stimuli  whose  agency  is  less  general,  that  it  is  rather  relative 
than  absolute;  being  frequently  dependent  upon  the  degree  of  change, 
rather  than  upon  the  actual  measure  of  the  amount  of  the  stimulus. 
This  constitutes  a  marked  difference  between  the  influence  of  these 
stimuli  on  mere  chemical  compounds,  and  their  operation  on  bodies 
endowed  with  vitality.  In  the  former  case,  their  action  is  always 
uniform ;  thus  the  same  amount  of  heat,  the  same  exposure  to  light, 
the  same  charge  of  electricity,  would  be  required  to  produce  a  given 
Chemical  effect,  how  often  soever  the  action  might  be  repeated.  But 
this  is  not  the  case  with  living  bodies  ;  since  an  increase  or  diminution 
in  the  intensity  of  the  vital  stimuli,  which,  if  made  suddenly,  would  be 
scarcely  compatible  with  the  TOntinuance  of  Life,  may  be  so  brought 
about,  as  to  produce  no  marked  change  in  its  phenomena, — the  or- 
ganism possessing  a  certain  power  of  adapting  itself  to  conditions 
which  are  habitual  to  it,  and  thus  allowing  great  changes  in  these 
conditions  to  be  gradually  effected,  without  any  serious  disturbance. — 
Thus  of  two  individuals  of  the  same  species,  one  may  become  torpid 
at  a  temperature  of  60°,  because  it  has  been  accustomed  to  a  tempe- 
rature of  70° ;  whilst  another,  habituated  to  a  temperature  of  60°, 
would  require  to  be  cooled  down  to  50°,  in  order  to  induce  torpidity  ; 
— the  influence  of  temperature  upon  the  vital  conditions  being  propor- 
tioned, more  to  the  variation  from  the  usual  standard,  than  to  the  actual 
elevation  of  that  standard.  Yet  the  first  of  these  individuals  might 
be  gradually  habituated  to  live  in  the  same  temperature  with  the 
second  ;  and  to  require  the  same  amount  of  further  depression  to  in- 
duce torpidity.  (See  §  129.) 

78.  It  is  a  very  curious  fact  that,  whilst  the  lower  classes  of  living 
beings  are  more  capable  than  the  higher  of  bearing  the  deprivation  of 
these  Vital  stimula,  they  are  at  the  same  time  more  liable  to  alterations 
in  their  own  structure  and  development,  in  consequence  of  variations 
in  the  degree  of  their  agency,  or  from  other  causes  external  to  them- 
selves. Thus  ihe.  forms  of  the  lower  tribes  of  Plants  and  Animals  are 
liable  to  be  greatly  affected  by  the  conditions  under  which  they  grow  ; 
and  these  especially  modify  their  degree  of  development.  It  seems 
as  if  the  formative  power  were  less  vigorous  in  the  lower,  than  in  the 
higher  classes  ;  so  that  the  mode  in  which  it  manifests  itself  in  the 
former  is  more  dependent  upon  external  influences  ;  whilst  in  the 
latter  it  either  predominates  over  them,  causing  the  regular  actions 


OF  LIGHT  AS  A  VITAL  STIMULUS.  61 

to  be  performed,  or  gives  way  altogether. — The  same  principle  applies 
to  the  early  condition  of  the  higher  organisms ;  their  embryos,  like 
those  beings  of  permanently  low  type  which  they  resemble  in  degree 
of  development,  being  liable  to  be  affected  by  modifying  causes, 
which  the  perfect  beings  of  the  same  kind  are  able  to  resist.  It  is  in 
this  way  that  we  are  to  explain  the  influence,  which  the  female  parent 
exerts  upon  the  embryo  ;  the  germ  of  which  she  receives  from  the 
male,  but  to  which  she  supplies  the  materials  for  its  development. 

1.   0/  Light ^  as  a  Condition  of  Vital  Action. 

79.  The  importance  of  this  agent,  not  only  to  the  Vegetable,  but 
to  the  Animal  World,  is  not  in  general  sufficiently  estimated.  Under 
its  influence  alone,  can  the  first  process  be  accomplished,  by  which 
inorganic  matter  is  transformed  into  ^an  organic  compound,  adapted 
by  its  nature  and  properties  to  form  part  of  the  organized  fabric.  The 
following  is  an  example  of  the  simplest  phenomenon  of  this  kind; 
and  it  demonstrates  the  influence  of  Light  the  more  clearly  on  account 
of  that  simplicity.  "  If  we  expose  some  spring-water  to  the  sunshine, 
though  it  may  have  been  clear  and  transparent  at  first,  it  presently 
begins  to  assume  a  greenish  tint ;  and,  after  a  while,  flocks  of  green 
matter  collect  on  the  sides  of  the  vessel,  in  which  it  is  contained.  On 
these  flocks,  whenever  the  sun  is  shining,  bubbles  of  gas  may  be  seen, 
which,  if  collected,  prove  to  be  a  mixture  of  oxygen  and  nitrogen, 
the  proportion  of  the  two  being  variable.  Meanwhile  the  green  matter 
rapidly  grows ;  its  new  parts  as  they  are  developed,  being  all  day 
long  covered  with  air-bells  which  disappear  as  soon  as  the  sun  has 
set.  If  these  observations  be  made  upon  a  stream  of  water,  the  cur- 
rent of  which  runs  slowly,  it  will  be  discovered  that  the  green  matter 
serves  as  food  for  thousands  of  aquatic  Insects,  which  make  their 
habitations  in  it.  These  insects  are  endowed  with  powers  of  rapid 
locomotion,  and  possess  a  highly  organized  structure ;  in  their  turn 
they  fall  a  prey  to  the  Fishes  which  frequent  such  streams."*  Such  is 
the  general  succession  of  nutritive  actions  in  the  Organized  Creation. 
The  highest  Animal  is  either  directly  dependent  upon  the  Vegetable 
Kingdom  for  the  materials  of  its  fabric,  or  it  is  furnished  with  these 
by  some  other  Animal,  this  again  (it  may  be)  by  another,  and  so  on  ; 
the  last  in  the  series  being  always  necessitated  to  find  its  support  in 
the  Vegetable  kingdom,  since  the  Animal  does  not  possess  the  power 
of  causing  the  Inorganic  elements  to  unite  into  even  the  simplest 
Organic  compound.  This  power  is  possessed,  in  a  high  degree  by 
Plants  ;  but  it  can  only  be  exercised  under  the  influence  of  Light. 
We  shall  now  examine,  more  in  detail,  the  conditions  of  this  influence, 
both  in  the  instance  just  quoted,  and  in  others  drawn  from  the  actions 
of  the  higher  Vegetable  organisms. 

80.  The  "  green  matter  of  Priestley,"  (as  it  is  commonly  called,) 

•  Prof.  Draper,  on  the  Forces  which  produce  the  Organization  of  Plants,  p.  15. 


62  OF  LIGHT  AS  A  VITAL  STIMULUS. 

which  makes  its  appearance  when  water  of  average  purity  is  sub- 
mitted to  the  action  of  the  Sun's  light,  and  which  also  pnesents  itself 
on  the  surface  of  walls  and  rocks,  that  are  constantly  kept  damp,  is 
now  known  by  Botanists  to  consist  of  cells  in  various  stages  of  de- 
velopment,— the  early  forms,  it  may  be,  of  several  different  species  of 
Confervee.  That  these  cells  all  originate  from  germs,  and  not  from 
any  direct  combination  of  the  inorganic  elements,  appears  not  only 
from  general  considerations,  but  also  from  the  fact  that,  if  measures 
be  taken  to  free  the  water  entirely  from  any  possible  infusion  of  or- 
ganic matter,  and  to  admit  into  contact  with  it  such  air  alone  as  has 
undergone  a  similar  purification,  no  green  flocks  make  their  appear- 
ance, under  the  prolonged  influence  of  the  strongest  sunlight.  We 
find,  then,  that  the  presence  of  a  germ  is  one  of  the  conditions  indis- 
pensable to  the  chemical  transformation  in  question.  It  maybe  asked 
how  it  can  be  certainly  ascertained  that  light  and  not  heat  is  the 
essential  condition  of  this  process ;  seeing  that  the  two  agents  are 
combined  in  the  solar  beam.  To  this  it  may  be  replied,  that  a  certain 
moderate  amount  of  heat  is  undoubtedly  necessary  ;  but  that  no  degree 
of  heat  without  light  will  be  effectual  in  producing  the  change,  as  is 
easily  proved  by  exposing  the  water  to  warmth  in  a  dark  place. 
Moreover,  when  a  certain  measure  of  light  is  afforded,  variations  in 
the  amount  of  heat  make  very  little  difference ;  but  we  shall  presently 
see  that  under  the  same  degree  of  heat,  the  amount  of  the  change  is 
directly  proportional  to  the  intensity  of  the  light.  Although,  there- 
fore, heat  furnishes  an  essential  condition,  it  cannot  be  questioned 
that  light  is  the  chief  stimulus  to  that  process,  by  which  the  germ 
brings  into  union  the  elements  to  be  employed  in  the  development  of 
its  own  fabric. 

81.  The  next  question  is, — What  are  these  elements,  and  whence 
are  they  obtained  ?  All  water  that  is  long  exposed  to  the  atmosphere, 
absorbs  from  it  a  certain  amount  of  its  constituent  gases  ;  but  these 
do  not  enter  it  in  the  proportions  in  which  they  are  contained  in  the 
atmosphere  itself;  their  relative  quantities,  in  a  given  measure  of 
water,  being  proportioned  to  the  facility  with  which  they  are  respect- 
ively absorbed  by  the  liquid.  Thus  carbonic  acid  is  most  readily 
absorbable ;  oxygen  next,  and  nitrogen  least  so.  From  the  expe- 
riments of  Prof.  Draper  it  would  appear,  that  notwithstanding  the 
very  small  proportion  of  carbonic  acid  contained  in  the  atmosphere 
(usually  not  more  than  l-2000th  part),  it  forms  as  much  as  29  per 
cent,  of  the  whole  amount  of  air  expelled  from  water  by  boiling.  Of 
the  residue,  one-third  consists  of  oxygen,  and  the  remaining  two- 
thirds  of  nitrogen  ;  so  that  the  proportion  of  the  oxygen  to  the  nitro- 
gen is  as  one  to  two,  instead  of  being  one  io  four,  as  in  atmospheric 
air.  The  absolute  quantity  of  this  water-gas,  contained  in  any  mea- 
sure of  water,  is  subject  to  variation  with  the  temperature;  the  quan- 
tity being  diminished  as  the  temperature  rises. — Now  when  water 
thus  impregnated  with  carbonic  acid,  oxygen,  and  nitrogen,  and  con- 
taining the  germs  of  aquatic  plants,  is  exposed  to  the  sun's  light,  a 


J 


OF  LIGHT  AS  A  VITAL  STIMULUS.  63 

development  of  vegetable  structure  takes  place,  indicated  by  the  green 
flocculent  appearance,  as  already  mentioned.  If  the  changes,  which 
are  now  occurring  in  the  water,  be  examined,  we  find  that  the  carbo- 
nic acid  is  diminishing  in  amount ;  and  that  oxygen  is  being  evolved. 
The  growing  mass  increases  in  volume  and  weight ;  and  after  a  time 
exhausts  the  whole  carbonic  acid  originally  contained  in  the  water. 
If  then  it  be  prevented  from  receiving  an  additional  supply,  the  pro- 
cess stops ;  but  as  conducted  naturally,  there  is  a  free  exposure  to 
the  atmosphere,  through  which  carbonic  acid  is  diffused  ;  and  hence, 
as  fast  as  it  is  removed  by  decomposition,  it  is  restored  by  absorption. 

82.  Here  then  are  the  conditions  and  materials  ;  what  is  the  re- 
sult ?  As  a  consequent  of  the  conjoint  action  of  light  and  of  a  vege^ 
table  cell-germ,  with  a  moderate  degree  of  heat,  upon  carbonic  acid 
and  water,  we  find  a  vegetable  structure  produced,  whose  fabric  con- 
sists of  carbon,  united  with  the  elements  of  water.  Whether  this 
union  is  really  as  simple  and  direct,  as  is  implied  by  this  expression, 
or  whether  the  same  proportions  of  oxygen,  hydrogen,  and  carbon 
are  united  in  a  different  form,  is  not  a  matter  of  consequence  to  the 
present  inquiry  ;  the  general  fact  being,  that  by  the  decomposition  of 
the  carbonic  acid,  oxygen  is  set  free,  and  carbon  is  made  to  unite 
with  the  elements  of  water ;  so  as  to  form  an  organic  compound, 
which  is  appropriated  by  the  Vegetable  organism  as  the  material  for 
its  growth. — How  far  Light  is  also  concerned  in  the  production  of 
the  protein-compounds  (of  which  azote  forms  a  part),  that  are  pre- 
pared by  Plants  for  the  use  of  Animals,  has  not  been  yet  ascertained  ; 
but  it  is  probable  that  these  are  not  the  less  dependent  upon  its  agency 
for  their  formation,  since  they  are  generated  under  the  same  circum- 
stances with  the  preceding.  Indeed  it  may  be  questioned  whether  a 
minute  quantity  of  azote  is  not  an  essential  part  of  the  contents  of  every 
vegetable  cell,  though  it  does  not  enter  into  the  composition  of  the 
cell-wall. 

83.  The  process  whose  conditions  we  have  thus  examined,  is  car- 
ried on  in  the  individual  cells,  that  compose  the  highest  and  most 
complex  Plants,  precisely  as  in  those  which  constitute  the  entire  forms 
of  the  lowest.  Thus  if  a  few^  garden-seeds  of  any  kind  be  sown  in 
a  flower-pot,  and  be  caused  to  germinate  in  a  dark  room,  it  will  soon 
be  perceived  that  although  they  can  grow  for  a  time  without  the  influ- 
ence of  light,  that  time  is  limited  ;  the  weight  of  their  solid  contents 
diminishes,  although  their  hulk  may  increase  by  the  absorption  of 
water;  their  young  leaves,  if  any  should  be  put  forth,  are  of  a  yellow 
or  gray-white  colour,  and  they  soon  fade  away  and  die.  But  if 
these  plants  are  brought  out  sufficiently  soon  into  the  bright  sun- 
light, they  speedily  begin  to  turn  green,  they  unfold  their  leaves,  and 
evolve  their  different  parts  in  a  natural  way ;  and  the  proportion  of 
their  solid  contents  goes  on  increasing  from  day  to  day.  If  the  fabric 
be  then  subjeeted  to  chemical  analysis,  it  is  found  to  contain  oxygen, 
hydrogen,  carbon,  and  azote  ;  united  in  various  proportions,  so  as  to 
form  compounds  that  differ  in  the  various  species,  though  some, — 


64  OF  LIGHT  AS  A  VITAL  STIMULUS. 

such  as  gum,  starch,  and  cellulose, — are  the  same  in  all.  If  the 
plants  be  made  to  grow  in  closed  glass  vessels,  under  such  circum- 
stances that  an  examination  can  be  accurately  made  as  to  the  changes 
they  are  impressing  on  the  atmosphere,  it  is  discovered  that  they  are 
constantly  decomposing  its  carbonic  acid, — appropriating  its  carbon, 
and  setting  free  its  oxygen, — so  long  as  they  are  exposed  to  the  in- 
fluence of  sunshine  or  bright  daylight.  They  also  appropriate  a  part 
of  the  minute  quantity  of  ammonia  which  is  diffused  through  the 
atmosphere  ;  extracting  its  nitrogen  to  employ  it  in  the  production  of 
their  azotized  compounds.  It  is  capable  of  being  demonstrated  by 
experiment,  that  these  changes  are  confined  to  the  green  surfaces  of 
plants,  and  therefore  to  the  leaves  or  leaf-like  organs,  the  young 
shoots,  and  the  stems  of  herbaceous  plants,  or  of  those  in  which  (as 
in  the  Cactus  tribe)  the  leaves  are  wanting  and  the  enlarged  succu- 
lent stem  supplies  their  place.  When  these  surfaces  cease  to  become 
green,  the  decomposing  action  also  ceases;  carbon  is  no  longer  fixed, 
and  oxygen  set  free ;  but,  on  the  contrary,  carbonic  acid  is  exhaled : 
this  is  the  case  when  the  leaves  change  colour,  previously  to  their 
fall,  in  the  autumn.  The  compounds  which  are  thus  generated  in  the 
green  surfaces,  are  conveyed  to  the  remote  parts  of  the  fabric,  by  the 
circulation  of  the  sap,  and  become  the  materials  of  their  nutrition  ; 
and  thus  the  green  cells  of  the  leaves  have  exactly  the  same  function, 
in  ministering  to  the  growth  of  the  fabric  of  the  largest  tree,  which 
the  green  cells  of  the  humble  Conferva  perform  in  regard  to  them- 
selves alone. 

84.  It  has  been  already  mentioned,  that  the  decay  which  is  always 
taking  place  in  the  softer  vegetable  structures,  gives  rise  to  a  con- 
tinual production  of  carbonic  acid,  even  in  the  living  plant  ;  this 
process,  which  must  be  regarded  as  a  true  Respiration,  is  effected, 
as  in  Animals,  by  the  union  of  the  carbon  of  the  Plant  with  oxygen 
derived  from  the  atmosphere  ;  and  it  is  carried  on,  not  by  the  green 
parts  only,  but  also,  perhaps  chiefly,  by  the  darker  surfaces.  Being 
antagonized  during  the  day  by  the  converse  change  just  described, 
it  can  only  be  made  sensible,  by  placing  the  plants  for  a  time  in  an 
atmosphere  in  which  no  carbonic  acid  previously  existed  ;  and  it 
will  then  be  found  that,  even  in  full  daylight,  a  certain  amount  of 
that  gas  is  exhaled.  The  fact,  however,  becomes  much  more  obvious 
at  night,  or  in  darkness  ;  since  the  decomposition  of  the  surrounding 
carbonic  acid  by  the  green  surfaces  is  then  completely  at  a  stand, 
and  a  full  effect  of  the  respiratory  process  is  seen.  Moreover, 
when  a  plant  becomes  unhealthy,  from  too  long  confinement  in  a 
limited  atmosphere,  it  begins  to  exhale  more  carbonic  acid  than  it 
decomposes ;  and  the  same  is  the  case,  as  just  now  stated,  in  regard 
to  leaves  that  have  nearly  reached  the  term  of  their  lives.  It  does 
not  admit  of  question,  however,  that,  under  ordinary  circumstances, 
nearly  the  whole  carbon  of  a  slow-growing  plant  is  derived  from  the 
carbonic  acid  of  the  atmosphere  ;  either  directly  through  the  leaves, 
or  indirectly  by  absorption  through  the  roots ;  and  that  there  must  be 


OF  LIGHT  AS  A  VITAL  STIMULUS.  65 

a  vast  surplus,  therefore,  of  the  carbonic  acid  decomposed,  over  that 
which  is  exhaled,  during  the  whole  life  of  the  tree, — that  surplus  being 
in  fact  represented  by  the  total  amount-  of  carbon  contained  in  its 
tissues. 

85.  It  is  probable  that  the  minute  amount  of  carbonic  acid  at  pre- 
sent contained  in  the  atmosphere,  is  as  much  as  could  be  beneficially 
supplied  to  Plants,  under  the  average  amount  of  light  to  which  they 
are  subjected,  over  the  whole  globe,  and  throughout  the  year.  It  has 
been  clearly  shown,  that,  under  the  influence  of  strong  sunlight,  an 
atmosphere  containing  as  much,  as  7  or  8  per  cent,  of  carbonic  acid 
may  be  not  merely  tolerated  by  Plants,  but  may  be  positively  bene- 
ficial to  them,  producing  a  great  acceleration  in  their  growth  ;  but  as 
soon  as  the  light  is  withdrawn,  it  acts  upon  them  most  injuriously, 
causing  them  speedily  to  become  unhealthy,  and  altogether  destroying 
their  vitality,  if  they  are  long  subjected  to  it.  Under  more  cloudless 
skies  than  ours,  however,  the  continual  supply  of  a  larger  quantity  of 
carbonic  acid,  than  our  atmosphere  contains,  is  found  to  be  quite  com- 
patible with  healthy  vegetation ;  especially  in  the  case  of  Cryptoga- 
mic  plants,  w^hich  (as  wdll  be  presently  shown)  require  a  less  amount 
of  this  stimulus  than  those  of  a  higher  kind.  Thus  in  the  lake  Sol- 
fatara  in  Italy,  an  unusual  supply  of  carbonic  acid  is  afforded  by  the 
constant  escape  of  that  gas  from  fissures  in  the  bed  of  the  lake,  with 
a  violence  that  gives  to  the  water  an  appearance  of  ebullition  ;  and 
on  its  surface  there  are  numerous  floating  islands,  which  consist 
almost  entirely  of  Confervse  and  other  simple  cellular  plants,  growing 
most  luxuriantly  on  this  rich  pabulum.  And  it  has  been  remarked, 
that  the  vegetation  around  the  springs  in  the  valley  of  Gottingen, 
w^hich  abound  in  carbonic  acid,  is  very  rich  and  luxuriant;  appearing 
several  weeks  earlier  in  the  spring,  and  continuing  much  later  in  the 
autumn,  than  at  other  spots  in  the  same  district.  Many  circumstances 
lead  to  the  belief,  that  at  former  epochs  in  the  Earth's  history,  the 
atmosphere  was  much  more  highly  charged  with  carbonic  acid  than 
at  present ;  and  that  to  this  circumstance,  in  conjunction  with  a  more 
intense  and  constant  influence  of  light  and  heat,  we  are  to  attribute 
that  extraordinary  luxuriance  of  the  vegetation  of  those  periods,  of 
which  we  have  most  abundant  evidence,  in  the  vast  beds  of  disin- 
tegrated vegetable  matter — Coal — that  are  of  such  value  to  Man,  and 
in  the  remains  which  have  been  more  perfectly  preserved  to  us,  and 
which  indicate  that  not  only  the  general  forest-mass,  but  many  of  the 
individual  forms  attained  a  degree  of  development,  which  cannot 
now  be  paralleled  even  between  the  Tropics. 

86.  Various  experiments  have  been  recently  made,  with  the  view 
of  determining  more  precisely  the  conditions  under  w^hich  Light  acts, 
in  producing  the  chemical  changes  that  have  been  now  discussed. 
These  experiments  for  the  most  part  agree  in  the  very  interesting  re- 
sult, that  the  amount  of  carbonic  acid  decomposed  by  plants  subjected 
to  the  differently  coloured  rays  of  the  solar  spectrum,  but  otherwise 
placed  in  similar  circumstances,  varies  with  the  illuminatwg  power 

5 


66  OF  LIGHT  AS  A  VITAL  STIMULUS. 

of  the  rays,  and  not  with  their  heating  or  their  chemical  power.  The 
method  adopted  by  Prof.  Draper,  which  seems  altogether  the  most 
satisfactory,  consisted  in  exposing  leaves  of  grass,  in  tubes  filled  with 
water  which  had  been  saturated  with  carbonic  acid  (after  the  expul- 
sion of  the  previously  dissolved  air  by  boiling),  to  the  influence  of 
the  different  rays  of  the  solar  spectrum,  dispersed  by  a  prism;  these 
were  kept  motionless  upon  the  tubes  for  a  sufficient  length  of  time, 
to  produce  an  active  decomposition  of  the  gas  in  the  tubes  which 
were  most  favourably  influenced  by  the  solar  beams  ;  and  the  relative 
quantities  of  the  oxygen  set  free  were  then  measured.  It  was  then 
evident  that  the  action  had  been  almost  entirely  confined  to  two  of 
the  tubes,  one  of  them  being  placed  in  the  red  and  orange  part  of  the 
spectrum,  and  the  other  in  the  yellow  and  green.  The  quantity  of 
carbonic  acid  decomposed  by  the  plant  in  the  latter  of  these,  was  to 
that  decomposed  in  the  former  in  the  ratio  of  nine  to  Jive;  the  quan- 
tity found  in  the  tube  that  had  been  placed  in  the  green  and  blue  por- 
tion of  the  spectrum,  would  not  amount,  in  the  same  proportion,  to 
one;  and  in  the  other  tubes,  it  was  either  absolutely  nothing,  or  ex- 
tremely minute.  Hence  it  is  obvious  that  the  yellow  ray,  verging  into 
orange  on  one  side,  and  into  green  on  the  other,  is  the  situation  of  the 
greatest  exciting  power  possessed  by  light  on  this  most  important  func- 
tion of  plants ;  and  as  this  coincides  with  the  seat  of  the  greatest  illu- 
minating power  of  the  spectrum,  it  can  scarcely  be  doubted  that  light 
is  the  agent  here  concerned ;  more  especially  as  the  place  of  greatest 
heat  is  in  the  red  ray,  and  that  of  greatest  chemical  power  is  in  the 
hlue^  both  of  which  rays  were  found  to  be  quite  inert  in  the  experi- 
ment just  quoted.  It  must  not  be  supposed  from  this  experiment, 
how^ever,  that  the  yellow  ray,  and  those  immediately  adjoining  it,  are 
the  only  sources  of  this  power  in  the  Solar  spectrum  ;  since  it  proves 
no  more  than  that,  when  the  leaves  were  exposed  to  a  highly  car- 
bonated atmosphere,  they  could  only  decompose  it  under  the  influence 
of  these  rays.  It  is  certain,  from  other  experiments,  that  plants  will 
grow,  in  an  ordinary  atmosphere,  under  rays  of  different  colours;  and 
it  appears  that  the  amount  of  carbon  they  severally  fix,  bears  a  con- 
stant proportion  to  the  illuminating  powers  of  the  respective  rays. 

87.  Although  this  fixation  of  carbon  by  the  decomposition  of  car- 
bonic acid,  is  the  most  universally-dependent,  of  all  the  processes  of 
the  Vegetable  economy,  upon  the  influence  of  Light,  yet  it  is  not  the 
only  one,  especially  among  the  higher  Plants,  in  which  that  agent 
becomes  an  important  condition.  Of  the  whole  quantity  of  moisture 
imbibed  by  the  roots,  and  contained  in  the  ascending  sap,  a  large 
proportion  is  exhaled  again  by  the  leaves ;  a  small  part  only  being 
retained  (together  with  the  substances  previously  dissolved  in  the 
whole)  to  form  part  of  the  fabric.  Now  upon  the  rapidity  of  this  ex- 
halation depends  the  rapidity  of  the  absorption  ;  for  the  roots  will  not 
continue  to  take  up  more  than  a  very  limited  amount  of  fluid,  when 
it  is  not  discharged  again  from  the  opposite  extremity  (so  to  speak) 
of  the  stem.     The  loss  of  fluid  by  the  leaves  appears  to  be  a  simple 


OF  LIGHT  AS  A  VITAL  STIMULUS.  67 

process  of  evaporation,  depending  in  great  part  upon  the  temperature 
and  dryness  of  the  surrounding  air;  this  evaporation,  however,  does 
not  take  place  solely,  or  even  chiefly,  from  the  external  surface  of  the 
leaves,  but  from  the  walls  of  the  passages  which  are  channeled  out  in 
their  interior.  Into  this  complex  labyrinth,  the  outer  air  finds  its  way 
through  orifices  in  the  cuticle,  which  are  termed  stomata  ;  and  through 
these  it  comes  forth  again,  charged  with  a  large  amount  of  vapour 
communicated  to  it  by  the  extensive  moist  surface,  with  which  it 
comes  into  contact  in  the  interior  of  the  leaf.  Now  the  stomata  are 
bounded  by  two  or  more  cells,  in  such  a  manner  that  they  can  be 
opened  or  closed  by  changes  in  the  form  of  these ;  and  this  alteration 
is  regulated  by  the  amount  of  Light,  to  which  the  leaves  are  sub- 
jected. When  the  stomata  are  opened  under  the  influence  of  light, 
the  external  air  is  freely  admitted  to  the  extended  surface  of  moist 
tissue  within  the  leaf,  and  a  rapid  loss  of  fluid  is  the  result;  more 
especially  if  the  temperature  be  high,  and  the  atmosphere  in  a  dry 
state.  On  the  other  hand,  if  the  stomata  be  closed,  the  only  loss  of 
fluid  that  can  take  place  from  the  internal  tissue  of  the  leaves,  is 
through  the  cuticle ;  the  organization  of  which  seems  destined  to 
enable  it  to  resist  evaporation,  so  that  the  exhalation  is  almost  entirely 
checked.  The  influence  of  light  upon  this  important  function  is 
easily  shown  by  experiment.  If  a  plant,  which  is  actively  transpiring 
and  absorbing  under  a  strong  sunshine,  be  carried  into  a  dark  room, 
both  these  operations  are  almost  immediately  checked,  even  though 
the  surrounding  temperature  be  higher  than  that,  to  which  the  plant 
was  previously  exposed. 

88.  The  effect  of  the  complete  and  continued  withdrawal  of  light 
from  a  growing  plant,  is  to  produce  an  etiolation  or  blanching  of  its 
green  surfaces;  a  loss  of  weight  of  the  solid  parts,  owing  to  the  con- 
tinued disengagement  of  carbon  from  its  tissues,  unbalanced  by  the 
fixation  of  that  element  from  the  atmosphere ;  a  dropsical  distension 
of  the  tissues,  in  consequence  of  the  continued  absorption  of  water, 
which  is  not  got  rid  of  by  exhalation ;  a  want  of  power  to  form  its 
peculiar  secretions,  or  even  to  generate  new  tissues,  after  the  mate- 
rials previously  stored  up  have  been  exhausted;  in  fine,  a  cessation 
of  all  the  operations  most  necessary  to  the  preservation  of  the  vitality 
of  the  structure,  of  which  cessation  its  death  is  the  inevitable  result. 
A  partial  withdrawal  of  the  influence  of  light,  however,  is  frequently 
used  by  the  Cultivator,  as  a  means  of  giving  an  esculent  character  to 
certain  Plants,  which  would  be  otherwise  altogether  uneatable  ;  for 
in  this  manner  their  tissues  are  rendered  more  succulent  and  less 
stringy,  whilst  their  peculiar  secretions  are  formed  in  diminished 
amount,  and  communicate  an  agreeable  flavour  instead  of  an  un- 
wholesome rankness  of  taste. 

89.  There  is  one  period  in  the  life  of  the  Flowering  Plant,  how- 
ever, in  which  the  influence  of  Light  is  injurious  instead  of  beneficial ; 
this  is  during  the  first  part  of  the  process  of  germination  of  seeds, 
w^hich  is  decidedly  retarded  by  its  agency.     This  forms  no  exception, 


68  OF  LIGHT  AS  A  VITAL  STIMULUS. 

however,  to  the  general  rule  ;  since  the  decomposition  of  the  carbonic 
acid  of  the  atmosphere,  and  the  fixation  of  carbon  in  the  tissues,  do 
not  constitute  a  part  of  it ;  on  the  contrary,  the  chemical  changes  that 
take  place  in  that  substance  of  the  seed,  which  has  been  stored  up 
for  the  nutrition  of  the  embryo,  involve  the  opposite  change, — the 
extrication  of  carbon,  which  is  converted  into  carbonic  acid  by  unit- 
ing with  the  oxygen  of  the  atmosphere.  It  is  obvious,  then,  why 
light  should  not  only  be  useless,  but  even  prejudicial,  to  this  process  ; 
since  it  tends  to  fix  the  carbon  in  the  tissues,  which  ought  to  be 
thrown  off.  As  soon,  however,  as  the  cotyledons  or  seed-leaves  are 
unfolded,  the  influence  of  light  upon  them  becomes  as  important,  as 
it  is  on  the  ordinary  leaves  at  a  subsequent  time ;  their  surfaces  be- 
come green,  and  the  fixation  of  carbon  from  the  atmosphere  com- 
mences. Up  to  that  point,  the  young  plant  is  diminishing  day  by 
day  (like  a  plant  that  is  undergoing  etiolation),  as  to  the  weight  of  its 
solid  contents ;  although  its  bulk  is  increased  by  the  absorption  of 
water.  From  the  time,  however,  that  its  cotyledons  begin  to  act 
upon  the  air,  through  the  stimulus  of  light,  the  quantity  of  solid  mat- 
ter begins  to  increase  ;  and  its  augmentation  subsequently  takes  place, 
at  a  rate  proportional  to  the  amount  of  green  surface  exposed,  and  the 
degree  of  light  to  which  it  is  subjected. 

90.  The  influence  of  Light  upon  the  direction  of  the  growing  parts 
of  Plants,  upon  the  opening  and  closing  of  flowers,  &c.,  is  probably 
due  to  its  share  in  the  operations  already  detailed.  Thus  the  green 
parts  of  Plants,  or  those  which  effect  the  decomposition  of  carbonic 
acid  (such  as  the  leaves  and  stems),  have  a  tendency  to  grow  towards 
the  light;  whilst  the  roots,  through  whose  dark  surfaces  carbonic  acid 
is  thrown  out  by  respiration,  have  an  equal  tendency  to  avoid  it. 
That  the  first  direction  of  the  stems  and  roots  of  plants  is  very  much 
influenced  in  this  manner,  appears  from  the  fact,  that,  by  reflecting 
light  upon  germinating  seeds,  in  such  a  manner  as  that  it  shall  only 
fall  upon  them  from  below,  the  stems  are  caused  to  direct  themselves 
downwards,  whilst  the  roots  grow  upwards.  There  can  be  no  doubt, 
however,  that  Light  has  also  a  more  direct  influence  on  the  develop- 
ment of  particular  organs  in  certain  Vegetables.  Thus  when  the 
gemmules*  of  the  Marchantia  polymorpha  (one  of  the  Hepaticce  or 
Liverworts)  are  in  process  of  development,  it  has  been  shown  by 
repeated  experiments,  that  stomata  are  formed  on  the  side  exposed  to 
the  light,  and  that  roots  grow  from  the  lower  surface  ;  and  that  it  is 
a  matter  of  indifference  which  side  of  the  little  disk  is  at  first  turned 
upwards,  since  each  has  the  power  of  developing  stomata,  or  roots, 
according  to  the  influence  it  receives.  After  the  tendency  to  the  for- 
mation of  these  organs  has  once  been  given,  however,  by  the  suflS- 
ciently  prolonged  influence  of  light  upon  one  side,  and  of  darkness 

*  These  geramules  are  analogous  to  the  buds  of  higher  plants;  and  they  consist  of 
little  collections  of  cells,  arranged  in  the  form  of  flat  disks;  which  are  at  first  attached 
by  footstalks  to  the  parent  plant,  but  afterwards  fall  off",  and  are  developed  into  new 
iadividuals. 


I 


OF  LIGHT  AS  A  VITAL  STIMULUS.  69 

and  moisture  upon  the  other,  any  attempt  to  alter  it  is  found  to  be 
vain;  for  if  the  surfaces  be  then  inverted,  they  are  soon  restored  to 
their  original  aspect  by  the  twisting  growth  of  the  plant. 

91.  The  same  amount  of  this  stimulus  is  not  requisite  or  desirable 
for  all  Plants ;  and  we  find  in  the  different  habitats  which  are  charac- 
teristic of  different  species,  even  amongst  our  native  plants,  that  the 
amount  congenial  to  each  varies  considerably.  Generally  speakings 
the  succulent  thick-leaved  Plants  require  the  largest  amount  ;  their 
stomata  are  few  in  number;  and  the  full  influence  of  light  is  requisite 
to  induce  sufficient  activity  in  the  exhaling  process ;  accordingly  we 
find  them  growing,  for  the  most  part,  in  exposed  situations,  where 
there  is  nothing  to  interfere  with  the  full  influence  of  the  solar  rays. 
On  the  other  hand,  plants  w^ith  thinner  and  more  delicate  leaves,  in 
which  the  exhaling  process  is  easily  excited  to  an  excessive  amount, 
evidently  find  a  congenial  home  in  more  sheltered  situations  ;  and 
there  are  some  which  can  only  develop  themselves  in  full  luxuriance 
in  the  deep  shades  of  a  plantation  or  a  forest.  By  a  farther  adaptation 
of  the  same  kind,  some  species  of  Plants  are  enabled  to  live  and 
acquire  their  green  colour,  under  an  amount  of  deprivation  which 
would  be  fatal  to  most  others ;  thus  in  the  mines  of  Freyberg,  in  which 
the  quantity  of  light  admitted  must  be  almost  infinitesimally  small, 
Humboldt  met  with  Flowering-Plants  of  various  species  ;  and  Mustard 
and  Cress  have  been  raised  in  the  dark  abysses  of  the  colleries  of 
this  country. 

92.  Generally  speaking,  however,  the  Cryptogamia  would  seem  to 
be  better  adapted  than  Flowering-Plants,  to  carry  on  their  vegetating 
processes  under  a  low  or  very  moderate  amount  of  this  stimulus. 
Thus  Humboldt  found  a  species  of  Sea-weed  near  the  Canaries, 
which  possessed  a  bright  grass-green  hue,  although  it  had  grown  at 
a  depth  of  190  feet  in  the  sea,  where,  according  to  computation,  it 
could  have  received  only  l-1500th  part  of  the  solar  rays  that  would 
have  fallen  upon  it  at  the  surface  of  the  ocean.  Many  Ferns,  Mosses, 
and  Lichens  seem  as  if  they  avoided  the  light,  choosing  the  northern 
rather  than  the  southern  sides  of  hedges,  buildings,  &c.,  for  their  resi- 
dence; so  that  the  former  often  present  a  luxuriant  growth  of  Crypto- 
gamic  vegetation,  whilst  the  latter  are  comparatively  bare.  It  must 
not  be  supposed,  however,  that  they  avoid  light  altogether,  but  only 
what  is  to  them  an  excessive  degree  of  it.  The  avoidance  of  light 
seems  to  be  much  stronger  in  the  Fungi,  which  grow  most  luxuriantly 
in  very  dark  situations ;  and  the  reason  of  this  is  probably  to  be  found 
in  the  fact,  that,  like  the  germinating  seed,  they  form  rather  than  de- 
compose carbonic  acid ;  their  food  being  supplied  to  them  from  the 
decaying  substances  on  which  they  grow  ;  and  the  rapid  changes  in 
their  tissues  giving  rise  to  a  high  amount  of  Respiration, — a  change 
exactly  the  converse  of  that,  on  which,  as  we  have  seen.  Light  exerts 
such  a  remarkable  stimulating  power. 

93.  In  regard  to  the  influence  of  Light  upon  the  functions  of  Ani- 
mals, comparatively  little  is  certainly  known.     It  is  evident  that  the 


70  OF  LIGHT  AS  A  VITAL  STIMULUS. 

influence  it  exerts  on  those  chemical  processes,  which  constitute  the 
first  stage  of  Vegetable  nutrition,  can  have  scarcely  any  place  in  Ani- 
mals; because  they  do  not  perform  any  such  acts  of  combination,  but 
make  use  of  the  products  already  prepared  for  them  by  Plants.  Hence 
we  do  not  find  that  the  surface  of  Animals  undergoes  that  extension, 
for  the  purpose  of  being  exposed  to  the  solar  rays,  which  is  so  cha- 
racteristic a  feature  in  the  Vegetable  fabric,  and  so  important  in  its 
economy.  Still  there  can  be  no  doubt,  that  the  degree  of  exposure  to 
light  has  a  great  influence  upon  the  colours  of  the  Animal  surface ;  and 
here  we  seem  to  have  a  manifestation  of  Chemical  agency,  analogous 
to  that  which  gives  colour  to  the  Vegetable  surface.  Thus  it  is  a  mat- 
ter of  familiar  experience,  that  the  influence  of  light  upon  the  skin  of 
many  persons,  causes  it  to  become  spotted  with  hvov^'i\  freckles;  these 
freckles  being  aggregations  of  brown  pigment-cells,  which  either 
owed  their  development  to  the  stimulus  of  light,  or  were  enabled  by 
its  agency  to  perform  a  chemical  transformation  which  they  could  not 
otherwise  eflfect.  In  like  manner,  the  swarthy  hue  which  many  per- 
sons acquire  in  warm  climates,  is  due  to  a  development  of  dark  pig- 
ment-cells diffused  through  the  epidermis;  and  an  increased  develop- 
ment of  the  same  kind  gives  rise  to  the  blackness  of  the  Negro-skin. 
There  can  be  no  doubt  that  the  prolonged  influence  of  light  upon  one 
generation  after  another,  tends  to  give  a  permanent  character  to  this 
variety  of  hue;  which  will  probably  be  more  easily  acquired,  in  pro- 
portion to  the  previously-existing  tendency  to  that  change.  Thus  it 
is  well  known  that  a  colony  of  Portuguese  Jews,  which  settled  at 
Tranquebar  about  three  centuries  ago,  and  which  has  kept  itself  dis- 
tinct from  the  surrounding  tribes,  cannot  now  be  distinguished,  as  to 
colour,  from  the  native  Hindoos.  But  it  is  probable  that  a  similar 
colony  of  fair-skinned  Saxons  would  not,  in  the  same  time,  have 
acquired  anything  like  the  same  depth  of  colour  in  their  skins. 

94.  There  can  be  no  doubt  that  the  brilliancy  of  colour,  which  is 
characteristic  of  many  tribes  of  animals  in  tropical  climates,  espe- 
cially Birds  and  Insects,  is  in  great  part  dependent,  like  the  bright- 
ness of  the  foliage  and  fruit  of  the  same  countries,  upon  the  brightness 
of  the  light  to  which  their  surfaces  are  exposed.  When  birds  of 
warm  climates,  distinguished  by  the  splendour  of  their  plumage,  are 
reared  under  an  artificial  temperature  in  our  own  country,  it  is  uni- 
formly observed  that  they  are  much  longer  in  acquiring  the  hues 
characteristic  of  the  adult ;  and  that  these  are  never  so  bright,  as 
when  they  have  been  produced  by  the  influence  of  the  tropical  sun. 
And  it  has  been  also  remarked,  that  if  certain  Insects  (the  Cockroach 
for  example),  which  naturally  inhabit  dark  places,  be  reared  in  an 
entire  seclusion  from  light,  they  grow  up  almost  as  colourless  as 
Plants  that  are  made  to  vegetate  under  similar  circumstances. 

95.  There  is  abundant  proof  that  Light  exercises  an  important  in- 
fluence on  the  processes  of  development  in  Animals,  no  less  than  in 
Plants.  Thus,  the  appearance  of  Animalcules  in  infusions  of  decaying 
organic  matter  is  much  retarded,  if  the  vessel  be  altogether  secluded 


OF  LIGHT  AS  A  VITAL  STIMULUS.  7X 

from  it.  The  rapidity  with  which  the  small  Entomostracous  Crusta- 
cea (Water-Fleas,  &c.),  of  our  pools,  undergo  their  transformations, 
has  been  found  to  be  much  influenced  by  the  amount  of  light  to  which 
they  are  exposed.  And  it  has  been  ascertained  that,  if  equal  numbers 
of  Silk-worm's  eggs  be  preserved  in  a  dark  room,  and  exposed  to 
common  daylight,  a  much  larger  proportion  of  larvae  are  hatched 
from  the  latter  than  from  the  former. — The  most  striking  proof  of  the 
influence  of  Light  on  animal  development,  however,  is  afforded  by 
the  experiments  of  Dr.  Edwards.  He  has  shown  that,  if  Tadpoles 
be  nourished  with  proper  food,  and  be  exposed  to  the  constantly- 
renewed  contact  of  water  (so  that  their  respiration  may  be  freely 
carried  on,  whilst  they  remain  in  their  Fish-like  condition),  but  be 
entirely  deprived  of  light,  their  growth  continues,  but  their  meta- 
morphosis into  the  condition  of  air-breathing  animals  is  arrested,  and 
they  remain  in  the  condition  of  large  tadpoles. — Numerous  facts, 
collected  from  different  sources,  lead  to  the  belief  that  the  healthy 
development  of  the  Human  body,  and  the  rapidity  of  its  recovery 
from  disease,  are  greatly  influenced  by  the  amount  of  light  to  which 
it  has  been  exposed.  It  has  been  observed,  on  the  one  hand,  that  a 
remarkable  freedom  from  deformity  exists  amongst  nations  who  wear 
very  little  clothing ;  whilst,  on  the  other,  it  appears  certain  that  an 
unusual  tendency  to  deformity  is  to  be  found  among  persons  brought 
up  in  cellars  or  mines,  or  in  dark  and  narrow  streets.  Part  of  this 
difference  is  doubtless  owing  to  the  relative  purity  of  the  atmosphere 
in  the  former  case,  and  the  want  of  ventilation  in  the  latter;  but 
other  instances  might  be  quoted,  in  which  a  marked  variation  pre- 
sented itself,  under  circumstances  otherwise  the  same.  Thus,  it  has 
been  stated  by  Sir  A.  Wylie  (who  was  long  at  the  head  of  the  medical 
staff*  in  the  Russian  army),  that  the  cases  of  disease  on  the  dark  side 
of  an  extensive  barrack  at  St.  Petersburgh,  have  been  uniformly, 
for  many  years,  in  the  proportion  of  three  to  one,  to  those  on  the 
side  exposed  to  strong  light.  And  in  one  of  the  London  Hospitals, 
with  a  long  range  of  frontage  looking  nearly  due  north  and  south,  it 
has  been  observed  that  residence  in  the  south  wards  is  much  more 
conducive  to  the  welfare  of  the  patients,  than  in  those  on  the  north 
side  of  the  building. 

96.  These  facts  being  kept  in  view,  it  is  easy  to  perceive  that 
there  must  be  differences  among  the  various  species  of  Animals,  as 
among  those  of  Plants,  in  regard  to  the  degree  of  light  which  is 
congenial  to  them.  Among  the  lowest  tribes,  in  which  no  special 
organs  of  vision  exist,  there  is  evidently  a  susceptibility  to  the  in- 
fluence of  light,  which  appears  scarcely  to  deserve  the  name  of 
sensibility,  but  which  seems  rather  analogous  to  that  which  is  mani- 
fested by  Plants ;  thus  among  those  Polypes  which  are  not  fixed  to 
particular  spots,  and  amongst  Animalcules,  there  are  some  species 
which  seek  the  light,  and  others  which  shun  it.  And  it  appears 
from  various  observations  upon  the  depths  at  which  marine  animals 
are  found,  especially  from  the  extensive  series  of  facts  collected  by 


72  OF  HEAT  AS  A  VITAL  STIMULUS. 

Prof.  E.  Forbes,*  that  there  are  a  series  of  zones,  so  to  speak,  to  be 
met  with  in  descending  from  the  surface  towards  the  bottom  of  the 
ocean,  each  of  which  is  characterized  by  certain  species  of  animals 
peculiar  to  itself,  whilst  other  species  have  a  range  through  two  or 
more  of  the  zones  ; — the  extent  of  the  range  of  depth,  in  each  species, 
bearing  a  close  correspondence  with  the  extent  of  its  geographical 
distribution.  Now  there  can  be  no  doubt,  that  the  restriction  of 
particular  species  to  particular  zones  is  due  in  great  part  to  the 
degree  of  pressure  of  the  surrounding  medium  ;  but  there  can  be  as 
little  doubt,  that  the  variation  in  the  degree  of  light  also  exerts  a  most 
important  influence,  the  solar  rays  in  their  passage  through  sea  water 
being  subject  to  a  loss  of  one  half  for  every  seventeen  feet.  From 
the  results  of  Prof.  Forbes'  researches,  it  appears  that  no  species  of 
Invertebrated  animals  habitually  live  at  a  greater  depth  than  300 
fathoms  ;  and  although  Fishes  have  been  captured  at  a  depth  of  from 
500  to  600  fathoms,  it  is  probable  that  they  had  strayed  from  their  usual 
abodes.  It  is  interesting  to  remark,  that  the  Proteus  anguineus,  an 
animal  which  closely  corresponds  in  its  fully-developed  form  with  the 
transition  stage  between  the  Tadpole  and  the  Frog,  finds  a  congenial 
abode  in  the  dark  lakes  of  the  caverns  of  Styria  and  Carniola,  and  in 
the  underground  caverns  that  connect  them ; — thus  showing  its  adapta- 
tion to  a  condition,  which  keeps  down  to  the  same  standard  the  deve- 
lopment of  an  animal,  that  is  empowered  under  other  circumstances 
to  advance  beyond  it. 

2.    Of  Heat,  as  a  Condition  of  Vital  Action. 

97.  The  most  perfectly-organized  body,  supplied  with  all  the  other 
conditions  requisite  for  its  activity,  must  remain  completely  inert,  if 
it  do  not  receive  sufficient  stimulation  from  Heat.  The  influence 
which  this  agent  exerts  upon  living  beings,  is  far  more  remarkable 
than  its  effects  upon  inorganic  matter  ;  although  the  latter  are  usually 
more  obvious.  We  are  all  familiar  with  its  power  of'  producing  ex- 
pansion,— with  the  liquefaction  which  is  the  consequence  of  its  appli- 
cation to  solids, — with  the  evaporation  which  it  occasions  in  liquids, 
— and  with  the  enormous  repulsive  force  which  it  generates  among 
the  particles  of  vapours;  but  it  is  not  until  we  look  deeper  than  the 
surface,  that  we  perceive  how  immediate  is  the  dependence  of  every 
action  of  Life  upon  this  mysterious  agent.  The  temporary  or  perma- 
nent loss  of  vitality,  in  parts  of  the  body  subjected  to  extreme  cold, 
is  a  *'  glaring  instance"  of  the  effect  of  its  withdrawal.  This  change, 
however,  is  not  immediate.  Its  first  step  is  a  mere  depression  of  the 
vitality  of  the  part,  involving  a  partial  stagnation  of  the  capillary 
circulation,  diminution  of  sensibility,  and  want  of  muscular  power. 
But  the  continued  action  of  cold  on  the  surface,  not  compensated  by 
a  sufficient  generation  of  heat  within,  causes  the  circulation  of  the 

•  Report  on  the  Invertebrata  of  the  ^gean  Sea,  in  Transactions  of  British  Associ- 
ations, 1843. 


t 


( 


OF  HEAT  AS  A  VITAL  STIMULUS.  73 

part  to  be  completely  suspended ;  its  small  vessels  contract  so  that 
they  become  almost  emptied  of  blood,  its  sensibility  and  power  of 
movement  are  destroyed, — in  a  word,  its  vitality  is  completely  sus- 
pended. In  such  a  state,  a  timely  but  cautious  application  of  warmth 
may  produce  the  gradual  renewal  of  the  circulation,  and  the  restora- 
tion of  the  other  properties  of  the  part,  which  are  dependent  upon  that 
function  ;  but  any  abrupt  change  would  complete  the  mischief  which 
the  cold  has  begun ;  and  would  altogether  destroy,  by  the  violence  of 
the  reaction,  the  vitality  which  was  only  suspended,  causing  the  actual 
death  of  the  part.  Hence,  when  the  extremities  are  frost-bitten,  no- 
thing can  be  more  injurious  than  to  bring  them  near  a  fire ;  whilst  no 
treatment  has  been  found  so  safe  and  effectual,  as  the  rubbing  them 
with  snow. 

98.  The  influence  of  Heat  upon  Vital  activity,  is  attested  on  a 
larger  scale,  by  the  striking  contrast  between  the  dreary  barrenness 
of  Polar  regions,  and  the  luxuriant  richness  of  Tropical  countries, 
where  almost  every  spot  teems  with  Animal  and  Vegetable  life.  And 
the  alternation  of  Winter  and  Summer  in  temperate  climates,  may  be 
almost  said  to  bring  under  our  own  view  the  opposite  conditions  of 
those  two  extreme  cases.  The  effect  of  the  withdrawal  of  Heat  is 
most  obvious  in  the  Vegetable  kingdom  ;  since  all  its  operations  are 
dependent  upon  a  certain  supply  of  that  agent ;  and  in  no  case  are 
Plants  possessed  of  the  power  of  generating  that  supply  within  them- 
selves,— excepting  in  certain  organs  which  do  not  impart  it  to  the 
rest  of  the  structure.  When  the  temperature  of  the  air  falls  to  the 
freezing-point,  therefore,  we  find  all  the  operations  of  the  Vegetable 
economy  undergoing  a  complete  suspension ;  yet  a  very  trifling  rise 
will  produce  a  renewal  of  them.  It  is  not  only  in  Evergreens,  that 
the  vital  processes  continue  to  be  performed  to  a  certain  extent  during 
the  winter ;  for  there  is  abundant  evidence  that,  even  in  the  trunk  and 
branches  of  trees  unclothed  with  leaves,  a  circulation  of  sap  takes 
place,  whenever  there  is  even  a  slight  return  of  warmth.  In  this 
manner,  the  leaf-buds  are  gradually  prepared  during  the  milder  days 
of  winter,  so  as  to  be  ready  to  start  forth  into  full  development,  with 
the  returning  steady  warmth  of  spring. 

99.  The  influence  of  Heat  upon  Vegetation  is  easily  made  apparent 
by  experiment ;  in  fact  experimental  illustrations  of  it,  on  a  large 
scale,  are  daily  in  progress.  For  the  Gardener,  by  artificial  warmth, 
is  not  only  enabled  to  rear  with  success  the  plants  of  tropical  climates, 
whose  constitution  would  not  bear  the  chilling  influence  of  our  winter ; 
but  he  can  also,  in  some  degree,  invert  the  order  of  the  seasons,  and 
produce  both  blossom  and  fruit  from  the  plants  of  our  own  country, 
when  all  around  seems  dead.  This  process  o^  forcing,  however,  is 
unfavourable  to  the  health  and  prolonged  existence  of  the  plants  sub- 
jected to  it;  since  the  period  of  repose,  which  is  natural  to  them,  is 
interrupted;  and  they  are  caused,  as  it  were,  to  live  too  fast.  The 
same  result  occurs,  when  a  plant  or  tree  of  temperate  climates  is 
transported  to  the  tropics.     Within  a  very  short  period  after  one  crop 


74  OF  HEAT  AS  A  VITAL  STIMULUS. 

of  leaves  has  fallen  off,  a  new  one  makes  its  appearance.  This  goes 
through  all  its  changes  of  development  and  decay  more  rapidly  than 
it  would  do  in  its  native  clime  ;  and  in  its  turn  falls  off,  and  is  speedily 
succeeded  by  another.  Hence  the  fruit-trees  of  this  country,  trans- 
ported to  the  East  or  West  Indies,  bear  abundant  crops  of  leaves, — 
three,  perhaps,  in  one  year,  or  five  in  two  years, — but  little  or  no 
fruit ;  and  the  period  of  their  existence  is  much  shortened. 

100.  As  Plants  are  almost  wholly  dependent  upon  the  temperature 
of  the  surrounding  medium,  for  the  supply  of  Heat  necessary  for  their 
growth,  many  regions  must  have  been  devoid  of  Vegetable  life  alto- 
gether ;  if  there  were  not  a  remarkable  adaptation,  in  the  wants  of 
different  species,  to  the  various  degrees  of  temperature  of  the  habita- 
tions prepared  for  them.  Thus  we  see  the  Cacti  and  Euphorbise 
attaching  themselves  to  the  surface  of  the  most  arid  rocks  of  tropical 
regions,  luxuriating,  as  it  would  seem,  in  the  full  glare  of  the  vertical 
sun,  and  laying  up  a  store  of  moisture  from  the  periodical  rains,  of 
which  even  a  long-continued  drought  is  not  sufficient  to  deprive  them. 
The  Orchideous  tribe,  on  the  other  hand,  whose  greatest  develop- 
ment occurs  in  the  same  zone,  find  their  congenial  habitation  in  the 
depths  of  the  tangled  forests,  where,  with  scarcely  an  inferior  amount 
of  heat,  they  have  the  advantage  of  a  moister  atmosphere,  caused  by 
the  exhalations  of  the  trees  on  which  they  cling.  The  majestic  Tree- 
Fern,  again,  reaches  its  full  development  in  insular  situations;  where, 
with  a  moist  atmosphere,  it  can  secure  a  greater  equability  of  tempe- 
rature than  is  to  be  met  with  in  the  interior  of  the  vast  tropical  con- 
tinents. None  of  these  races  can  develop  themselves  elsewhere,  to 
their  full  extent,  at  least,  unless  their  natural  conditions  of  growth  are 
imitated  as  far  as  possible ;  and  in  proportion  as  this  imitation  can  be 
made  complete,  in  that  proportion  may  the  plant  of  the  tropics  be 
successfully  reared  in  temperate  regions. 

101.  There  are  some  examples  of  the  adaptation  of  particular 
forms  of  Vegetable  life  to  extremes  of  temperature,  which  are  inte- 
resting as  showing  the  extent  to  which  this  adaptation  may  be  carried. 
In  hot  springs  near  a  river  of  Louisiana,  of  the  temperature  of  from 
122°  to  145°,  there  have  been  seen  to  grow  not  merely  Confervae 
and  herbaceous  plants,  but  shrubs  and  trees  ;  and  a  hot-spring  in  the 
Manilla  islands,  which  raises  the  thermometer  to  187°,  has  plants 
flourishing  in  it,  and  on  its  borders.  A  species  of  Chara  has  been 
found  growing  and  reproducing  itself  in  one  of  the  hot-springs  of 
Iceland,  which  boiled  an  egg  in  four  minutes  ;  various  Confer vse,  &c., 
have  been  observed  in  the  boiling-springs  of  Arabia  and  the  Cape  of 
Good  Hope  ;  and  at  the  island  of  New  Amsterdam,  there  is  a  mud- 
spring,  which,  though  hotter  than  boiling-water,  gives  birth  to  a 
species  of  Liverwort.  On  the  other  hand,  there  are  some  forms  of 
Vegetation,  which  seem  to  luxuriate  in  degrees  of  cold,  that  are  fatal 
to  most  others.  Thus  the  Lichen,  which  serves  as  the  winter  food 
of  the  Rein-deer,  spreads  itself  over  the  ground  whilst  thickly  covered 
with  snow;  and  the  beautiful  little  Protococcus  nivalis j  or  Red  Snow, 


OF  HEAT  AS  A  VITAL  STIMULUS.  75 

reddens  extensive  tracts  in  the  arctic  regions,  where  the  perpetual 
frost  of  the  surface  scarcely  yields  to  the  influence  of  the  solar  rays  at 
Midsummer. 

102.  It  is,  for  the  most  part,  among  the  Cryptogamic  tribes, — the 
Ferns,  Mosses,  Liverworts,  Fungi,  and  Lichens, — that  the  greatest 
power  of  growing  under  a  low  temperature  exists ;  and  we  accord- 
ingly find  that  the  proportion  of  these  to  the  Phanerogamia,  or 
Flowering  Plants,  increases  as  we  proceed  from  the  Equator  towards 
the  Poles.  It  has  been  estimated  by  Humboldt,  that,  in  Tropical 
regions,  the  number  of  species  of  Cryptogamia  is  only  about  one-tenth 
that  of  the  Flowering  Plants  ;  in  the  part  of  the  Temperate  zone  which 
lies  between  Lat.  45°  and  52°,  the  proportion  rises  to  one-half;  and 
the  relative  amount  gradually  increases  as  we  proceed  towards  the 
Poles,  until,  between  Lat.  67°  and  70°,  the  number  of  species  of 
Cryptogamia  equals  that  of  the  Phanerogamia.  Among  the  Flowering 
Plants,  moreover,  the  greatest  endurance  of  cold  is  to  be  found  in 
those,  which  approach  most  nearly  to  the  Cryptogamia  in  the  low 
degree  of  their  development ;  thus  the  Glumaceous  group  of  Endo- 
gens,  including  the  Grasses,  Rushes,  and  Sedges,  which  forms  about 
one-eleventh  of  the  whole  amount  of  Phanerogamic  vegetation  in  the 
Tropics,  constitutes  one-fourth  of  it  in  the  Temperate  regions,  and 
one-third  in  the  Polar;  and  the  ratio  of  the  Gymnospermic  group  of 
Exogens,  which  chiefly  consists  of  the  Pine  and  Fir  tribe,  increases 
in  like  manner.  Still  the  influence  of  a  high  temperature  is  evident 
even  upon  the  Cryptogamia  and  their  allies ;  for  it  is  only  under  the 
influence  of  the  light  and  warmth  of  tropical  climes,  that  the  Ferns, 
— the  highest  among  the  former, — can  develop  a  woody  stem,  and 
assume  the  character  of  trees ;  and  it  is  only  there  that  the  tall  Sugar- 
Canes,  and  the  gigantic  Bamboos,  which  are  but  Grasses  on  a  large 
scale,  can  flourish. 

103.  It  appears,  then,  that  to  every  species  of  Vegetable  there  is 
a  temperature  which  is  most  congenial,  from  its  producing  the  most 
favourable  influence  on  its  general  vital  actions.  There  is  a  consi- 
derable difference  between  the  power  oi growing,  and  oi  flourishing^ 
at  a  given  temperature.  We  may  lower  the  heat  of  a  plant  to  such 
a  degree,  as  to  allow  it  to  continue  to  live ;  yet  its  conclition  will  be 
unhealthy.  It  absorbs  food  from  the  earth  and  air,  but  cannot  assi- 
milate and  convert  it.  Its  tissue  grows  but  becomes  distended  with 
water,  instead  of  being  rendered  firm  by  solid  deposits.  The  usual 
secretions  are  not  formed  ;  flavour,  sweetness,  and  nutritive  matter, 
are  each  diminished  ;  and  the  power  of  flowering  and  producing  fruit 
is  lost.  We  see  a  difference  in  the  amount  of  heat  required  for  the 
vegetating  processes,  even  in  the  various  species  indigenous  to  our 
own  climate ;  thus  the  common  Chickweed,  Groundsel,  and  Poa  annua 
evidently  grow  readily  at  a  temperature  but  little  above  the  freezing- 
point,  whilst  the  Nettles,  Mallows,  and  other  weeds  around  them, 
remain  torpid.  But  the  difference  is  much  more  strongly  marked  in 
the  vegetation  of  different  climates ;  showing  an  evident  adaptation 


76  OF  HEAT  AS  A  VITAL  STIMULUS. 

of  the  tribes  indigenous  to  each,  to  that  range  of  temperature  which 
they  will  there  experience.  Instead  of  being  scantily  supplied  with 
such  of  the  tropical  plants  as  could  support  a  stunted  and  precarious 
life  in  ungenial  climates,  the  temperate  regions  are  stocked  with  a 
multitude  of  vegetables  which  appear  to  be  constructed  expressly  for 
them ;  inasmuch  as  these  species  can  no  more  flourish  at  the  Equator, 
than  the  equatorial  species  can  in  these  Temperate  regions.  And 
such  new  supplies,  adapted  to  new  conditions,  recur  perpetually  as 
we  advance  tow^ards  the  apparently  frozen  and  untenantable  regions 
in  the  neighbourhood  of  the  Pole.  Every  zone  has  its  peculiar  vege- 
tables ;  and  while  w^e  miss  some,  we  find  others  making  their  appear- 
ance, as  if  to  replace  those  which  are  absent. 

104.  Thus  in  the  countries  lying  near  the  Equator,  the  vegetation 
consists  in  great  part  of  dense  forests  of  leafy  evergreen  trees.  Palms, 
Bamboos,  and  Tree-Ferns,  bound  together  by  clustering  Orchidea^ 
and  strong  creepers  of  various  kinds.  There  are  no  verdant  meadow^s, 
such  as  form  the  chief  beauty  of  our  temperate  regions  ;  and  the  lower 
orders  of  Vegetation  are  extremely  rare.  It  is  only  in  this  torrid  Zone, 
that  Dates,  Coffee,  Cocoa,  Bread-fruit,  Bananas,  Cinnamon,  Cloves, 
Nutmegs,  Pepper,  Myrrh,  Indigo,  Ebony,  Logwood,  Teak,  Sandal- 
wood, and  many  other  of  the  vegetable  products,  most  highly  valued 
for  their  flavour,  their  odour,  their  colour,  or  their  density,  come  to 
full  perfection.  As  we  recede  from  the  Equator,  we  find  the  leafy 
Evergreens  giving  place  to  trees  with  deciduous  leaves ;  rich  mea- 
dows appear,  abounding  with  tender  herbs ;  the  Orchideae  no  longer 
find  in  the  atmosphere,  and  on  the  surface  of  the  trees  over  which 
they  cluster,  a  sufficiency  of  moisture  for  their  support,  and  the  para- 
sitic species  are  replaced  by  others  which  grow  from  fleshy  roots 
implanted  in  the  soil;  but  aged  trunks  are  now  clothed  with  Mosses; 
decayed  vegetables  are  covered  with  parasitical  Fungi ;  and  the 
waters  abound  with  Confervse.  In  the  warmer  parts  of  the  tempe- 
rate regions,  the  Apricot,  Citron,  Orange,  Lemon,  Peach,  Fig,  Vine, 
Olive,  and  Pomegranate,  the  Myrtle,  Cedar,  Cypress,  and  Dwarf 
Palm,  find  their  congenial  abode.  These  give  place,  as  we  pass 
northwards,  to  the  Apple,  the  Plum,  and  the  Cherry,  the  Chestnut, 
the  Oak,  the  Elm,  and  the  Beech.  Going  further  still,  we  find  that 
the  fruit-trees  are  unable  to  flourish,  but  the  timber-trees  maintain 
their  ground.  Where  these  last  fail,  we  meet  \vith  extensive  forests 
of  the  various  species  of  Firs ;  the  Dwarf  Birches  and  Willows  replace 
the  larger  species  of  the  same  kind  ;  and  even  near  or  within  the  arc- 
tic circle,  we  find  wild  flowers  of  great  beauty, — the  Mezereon,  the 
yellow  and  white  Water-Lily,  and  the  Globe-flower.  Where  none  of 
these  can  flourish,  where  trees  wholly  disappear,  and  scarcely  any 
flowering-plants  are  to  be  met  with,  an  humbler  Cryptogamic  vegeta- 
tion still  raises  its  head,  in  proof  that  no  part  of  the  Globe  is  altogether 
unfit  for  the  residence  of  living  beings,  and  that  the  empire  of  Flora 
has  no  limit. 

105.  But  distance  from  the  Equator  is  by  no  means  the  only  ele- 


OF  HEAT  AS  A  VITAL  STIMULUS.  77 

ment,  in  the  determination- of  the  mean  temperature  of  a  particular 
spot,  and  of  the  Vegetation  which  is  congenial  to  it.  Its  height  above 
the  level  of  the  sea  is  equally  important ;  for  this  produces  a  variation 
in  the  amount  of  heat  derived  from  the  Sun,  at  least  as  great  as  that 
occasioned  by  difference  of  latitude.  Thus  it  is  not  alone  on  the 
summits  of  Hecla,  Mount  Blanc,  and  other  mountains  of  arctic  or 
temperate  regions,  that  we  find  a  coating  of  perpetual  snow  ;  we  find 
a  similar  covering  on  the  lofty  summits  of  the  Himalayan  chain,  which 
extends  to  within  a  few  degrees  of  the  tropic  of  Cancer ;  and  even  on 
the  higher  peaks  of  that  part  of  the  ridge  of  the  Andes,  which  lies 
immediately  beneath  the  Equator.  The  height  of  the  snow-line  be- 
neath the  Equator,  is  between  15,000  and  16,000  feet  above  the  level 
of  the  sea ;  on  the  south  side  of  the  Himalayan  ridge,  it  is  as  much 
as  17,000  feet,  but  on  the  north  side  only  13,000  feet;  and  in  the 
Swiss  Alps  it  is  about  8000  feet.  Its  position  is  very  much  affected, 
however,  by  local  circumstances,  such  as  the  neighbourhood  of  a  large 
expanse  of  land  or  of  sea ;  hence  the  small  quantity  of  land  in  the 
Southern  Hemisphere,  renders  its  climate  generally  so  much  colder 
than  that  of  the  Northern,  that  in  Sandwich  land  (which  is  Lat.  59°  S., 
or  in  the  same  parallel  as  the  north  of  Scotland),  the  whole  country, 
from  the  summits  of  the  mountains  down  to  the  very  brink  of  the 
sea-cliffs,  is  covered  many  fathoms  thick  with  everlasting  snow  ;  and 
in  the  island  of  Georgia  (which  is  in  Lat.  54°  S.,  or  in  the  same  paral- 
lel as  Yorkshire,)  the  limit  of  perpetual  snow  descends  to  the  level 
of  the  ocean,  the  partial  melting  in  summer  only  disclosing  a  few 
rocks,  scantily  covered  with  moss  and  tufts  of  grass.  Yet  the  highest 
mountains  of  Scotland,  w^hich  ascend  to  an  elevation  of  nearly  5000 
feet,  and  are  four  degrees  more  distant  from  the  equator,  do  not  attain 
the  limit  of  perpetual  snow  ;  this  is  reached,  however,  by  mountains 
in  Norway,  at  no  greater  elevation. 

106.  If,  then.  Temperature  exert  such  an  influence  on  Vegetation 
as  has  been  stated,  we  ought  to  find  on  the  sides  of  lofty  mountains 
in  tropical  regions  the  same  progressive  alterations  in  the  characters 
of  the  Plants  that  cover  them,  as  we  encounter  in  journeying  from 
t^e  equatorial  towards  the  polar  regions.  This  is  actually  the  case. 
The  proportion  of  Cryptogamia  to  Flowering  Plants,  for  example,  is  no 
more  than  one-fifteenth  on  the  plains  of  the  Equatorial  region  ;  whilst 
it  is  as  much  as  one-fifth  on  the  mountains.  In  ascending  the  Peak  of 
Teneriffe,  Humboldt  remarked  as  many  as  five  distinct  Zones,  which 
were  respectively  marked  by  the  products  w^hich  characterize  differ- 
ent climates.  Thus  at  the  base,  the  vegetation  is  altogether  tropical ; 
the  Date-Palm,  Plaintain,  Sugar-Cane,  Banyan,  the  succulent  Eu- 
phorbia, the  Draccena,  and  other  trees  and  plants  of  the  torrid  zone 
there  flourish.  A  little  higher  grow  the  Olive,  the  Vine,  and  other 
fruit-trees  of  Southern  Europe ;  there  Wheat  flourishes ;  and  there  the 
ground  is  covered  with  grassy  herbage.  Above  this  is  the  woody 
region,  in  which  are  found  the  Oak,  Laurel,  Arbutus,  and  other  beau- 
tiful hardy  evergreens.     Next  above  is  the  region  of  Pines;  charac- 


78  OF  HEAT  AS  A  VITAL  STIMULUS. 

terized  by  a  vast  forest  of  trees  resembling  the  Scottish  Fir,  inter- 
mixed with  Juniper.  This  gives  place  to  a  tract  remarkable  for  the 
abundance  of  Broom  ;  and  at  last  the  scenery  is  terminated  by  Scro- 
fularia,  Viola,  a  few  Grasses,  and  Cryptogamic  plants,  which  extend 
to  the  borders  of  the  perpetual  snow  that  caps  the  summit  of  the 
mountain. 

107.  The  effects  of  Temperature  on  Vegetation  are  not  only  seen 
in  its  influence  upon  the  Geographical  distribution  of  Plants,  that  is, 
in  the  limitation  of  particular  species  to  particular  climates;  for  they 
are  shown,  perhaps  even  more  remarkably,  in  the  variation  in  the  size 
of  individuals  of  the  same  species;  when  that  species  possesses  the 
power  of  adapting  itself  to  widely-different  conditions,  which  is 
the  case  with  some.  Thus  the  Cerasus  Virginiana  grows  in  the 
southern  states  of  North  America  as  a  noble  tree,  attaining  one  hun- 
dred feet  in  height ;  in  the  sandy  plains  of  the  Saskatchawan,  it  does 
not  exceed  twenty  feet ;  and  at  its  northern  limit,  the  Great  Slave 
Lake,  in  Lat.  62°,  it  is  reduced  to  a  shrub  of  five  feet.  Another 
curious  effect  of  heat  is  shown  in  its  influence  on  the  sexes  of  certain 
Monoecious  flowers ;  thus  Mr.  Knight  mentions  that  Cucumber  and 
Melon  plants  will  produce  none  but  male  or  staminiferous  flowers,  if 
their  vegetation  be  accelerated  by  heat;  and  all  female  or  pistillife- 
rous,  if  its  progress  be  retarded  by  cold. 

108.  The  injurious  influence  of  excessive  heat  can  be,  to  a  certain 
extent,  resisted  by  Plants,  through  the  cooling  process  kept  up  by  the 
continual  evaporation  of  moisture  from  their  surface.  But  the  power 
of  maintaining  this  cooling  process  entirely  depends  upon  the  supply 
of  fluid,  with  which  the  plant  is  furnished.  If  the  supply  be  adequate 
to  the  demand,  the  effect  of  heat  will  be  to  stimulate  all  the  vital  ope- 
rations of  the  plant,  and  to  cause  them  to  be  performed  with  increased 
energy  ;  though,  as  we  have  already  seen,  this  energy  may  be  such 
as  to  occasion  a  premature  exhaustion  in  its  powers,  by  the  excessive 
luxuriance  which  it  occasions.  But  if  the  supply  of  water  be  deficient, 
the  plant  is  burnt  up  by  the  continuance  of  heat  in  a  dry  atmosphere  ; 
and  it  either  withers  and  dies,  or  its  tissues  become  dense  and  con- 
tracted, without  losing  their  vitality.  Thus  it  has  been  remarked,  that 
shrubs  growing  among  the  sandy  deserts  of  the  East,  have  as  stunted 
an  appearance  as  those  attempting  to  vegetate  in  the  Arctic  regions ; 
their  leaves  being  converted  into  prickles,  and  their  leaf-buds  pro- 
longed into  thorns  instead  of  branches. — The  influence  of  excessive 
heat  in  destroying  life,  can  sometimes  be  traced  through  the  direct 
physical  changes  which  it  occasions  in  the  vegetable  tissues.  Thus 
it  has  been  ascertained  that  grains  of  corn  will  vegetate,  after  exposure 
to  water  or  vapour  possessing  a  considerable  degree  of  heat ;  provided 
that  heat  do  not  amount  to  144°  in  the  case  of  water,  and  167°  in  that 
of  vapour.  At  these  temperatures,  the  structure  of  the  seed  under- 
goes a  disorganizing  change,  by  the  rupture  of  the  vesicles  of  starch 
which  form  a  large  part  of  it ;  and  the  loss  of  its  power  of  germinating 
is  therefore  readily  accounted  for.     The  highest  temperature  which 


OF  HEAT  AS  A  VITAL  STIMULUS.  79 

the  soil  usually  possesses  in  tropical  climates,  is  about  126°,  though 
Humboldt  has  once  observed  the  thermometer  rise  to  140°.  Seeds 
imbedded  in  such  a  soil,  therefore,  may  not  lose  their  vitality,  although 
they  will  not  germinate  in  such  temperatures.  The  temperature  most 
favourable  to  germination  probably  varies  in  different  species,  and  is 
one  of  the  conditions  that  produces  their  adaptation  to  different 
climates.  Thus  it  appears  that  Corn  will  not  germinate  in  water  at  a 
higher  temperature  than  95°,  whilst  Maize  will  germinate  in  water  at 
113°  ;  and,  as  is  well  known,  Maize  will  flourish  in  countries  in  which 
Corn  cannot  be  grown. 

109.  We  must  not  confound  the  power  which  Plants  possess  of 
vegetating^  or  exhibiting  vital  activity,  under  widely-different  degrees 
of  temperature,  with  the  power  of  retaining  their  vitality  in  a  dormant 
condition,  which  many  of  them  possess  in  a  very  remarkable  degree. 
When  the  external  temperature  is  much  below  the  freezing-point,  it 
is  impossible  that  any  vegetating  processes  can  go  on  ;  since  the  Plant 
does  not  possess  the  power  of  generating  heat  within  itself.  Now 
such  a  complete  cessation  of  activity  is  quite  compatible,  in  many  in- 
stances, with  the  preservation  of  the  organized  structure  in  a  condition 
perfectly  unchanged,  and,  in  consequence,  with  the  continuance  of 
its  peculiar  properties ;  so  that  these  properties  may  be  again  called 
into  operation,  when  the  temperature  shall  have  risen.  But  in  other 
cases,  the  plant  may  be  killed  by  the  intensity  of  the  cold  ;  that  is,  the 
return  of  warmth  will  not  excite  it  to  activity.  We  have  occasion  to 
notice,  in  every  severe  winter,  the  difference  in  this  respect  amongst 
the  plants  which  are  cultivated  in  our  own  climate ;  some  of  them 
being  killed  by  a  hard  frost,  the  effects  of  which  are  resisted  by  others, 
even  though  their  situation  be  more  exposed.  In  general  it  will  be 
found,  that  the  cold  acts  most  powerfully  (as  might  be  expected)  upon 
plants  which  are  not  indigenous  to  our  country,  but  which  have  been 
introduced  and  naturalized  from  some  warmer  regions.  But  it  is 
worthy  of  note,  amongst  other  peculiarities  in  the  relation  of  Heat  and 
Vegetation,  that  many  plants  are  readily  killed  by  a  low  temperature, 
which  yet  flourish  well  under  a  very  moderate  amount  of  warmth  ;  so 
that  they  will  grow  in  situations  where  the  mean  temperature  of  the 
year  is  low  and  the  summers  cool,  provided  the  winters  are  not  severe ; 
whilst  they  cannot  be  preserved  without  special  protection,  in  situa- 
tions where  the  w^inters  are  colder,  even  though  the  summers  should 
be  much  hotter,  and  the  mean  temperature  of  the  whole  year  should  be 
considerably  higher.  Thus  there  are  shrubs  growing  in  the  Botanic 
Garden  of  Edinburgh,  which  cannot  be  safely  left  in  the  open  air  in 
the  neighbourhood  of  London,  and  which  would  be  most  certainly 
killed  by  the  winter-cold  of  central  France. 

110.  It  does  not  admit  of  doubt,  that  the  destructive  influence  of 
a  very  low  temperature  upon  the  Vitality  of  Plants,  is  immediately 
exerted  through  its  chemical  and  physical  effects  upon  the  tissues  and 
their  contents.  Thus  it  will  produce  congelation  of  their  fluids  ;  and 
the  expansion  which  takes  place  in  freezing  will  injure  the  walls  of 


80  OF  HEAT  AS  A  VITAL  STIMULUS. 

the  containing  cells, — distending,  lacerating,  or  even  bursting  them. 
The  same  cause  will  probably  occasion  the  expulsion  of  air  from  some 
parts  which  ought  to  contain  it ;  and  the  introduction  of  it  into  other 
parts  which  ought  to  be  filled  with  fluid.  And  a  separation  will  take 
place,  in  the  act  of  freezing,  between  the  constituent  parts  of  the 
vegetable  juices  ;  which  will  render  them  unfit  for  discharging  their 
functions,  when  returning  warmth  would  otherwise  call  them  into 
activity.  Hence  we  are  enabled  in  some  degree  to  account  for  the 
differences  in  the  power  of  resisting  cold,  which  the  various  species 
of  Plants,  and  even  the  various  parts  of  the  same  individual,  are  found 
to  possess.  For,  other  things  being  equal,  the  power  of  each  plant, 
and  of  each  part  of  a  plant,  to  resist  a  low  temperature,  will  be  in  the 
inverse  ratio  of  the  quantity  of  water  contained  in  the  tissue ;  thus,  a 
succulent  herbaceous  plant  suflfers  more  than  one  with  a  hard  woody 
stem  and  dense  secretions ;  and  young  shoots  are  destroyed  by  a  degree 
of  cold,  which  does  not  aflfect  old  shoots  and  branches  of  the  same 
shrub  or  tree.  Again,  the  viscidity  of  the  fluids  of  some  plants  is  an 
obstacle  to  their  congelation,  and  therefore  enables  them  to  resist 
cold ;  thus  it  is,  that  the  resinous  Pines  are,  of  all  trees,  those  which 
can  endure  the  lowest  temperature.  The  dimensions  of  the  cells,  too, 
of  which  the  tissue  is  composed,  appears  to  have  an  influence  ;  the 
liability  to  freeze  being  diminished  by  a  very  minute  subdivision  of 
the  fluids.  And  when  the  roots  are  implanted  deep  in  the  soil,  where 
the  temperature  does  not  fall  so  low  as  that  of  the  surface  by  many 
degrees,  the  fluidity  of  the  sap  may  be  maintained,  in  spite  of  an  ex- 
tremely cold  state  of  the  atmosphere. 

111.  It  is  in  Cryptogamic  plants,  that  the  greatest  power  of  sustain- 
ing cold  exists;  as  might  be  inferred  from  what  has  been  already  stated 
in  regard  to  their  geographical  distribution.  The  Little  Fungus  (7b- 
Tula  Cerevisice)  which  is  one  of  the  principal  constituents  of  Yeast, 
does  not  lose  its  vitality  by  exposure  to  a  temperature  of  76°  below 
zero;  though  it  requires  a  somewhat  elevated  temperature  for  its  active 
growth.  It  would  appear  that  Seeds  are  enabled  to  sustain  a  degree  of 
cold  without  the  loss  of  their  vitality,  which  would  be  fatal  to  growing 
plants  of  the  same  species;  thus  grains  of  corn,  of  various  kinds,  will 
germinate  after  being  exposed  for  a  quarter  of  an  hour  to  a  temperature 
equal  to  that  of  frozen  mercury.  It  is  not  diflficult  to  account  for  this, 
when  the  closeness  of  their  texture,  and  the  small  quantity  of  fluid 
which  it  includes,  are  kept  in  view.  The  act  of  Germination,  how- 
ever, will  only  take  place  under  a  rather  elevated  temperature  ;  and 
we  find  in  the  Chemical  changes  which  it  involves,  a  provision  for 
maintaining  this,  w^hen  the  process  has  once  commenced. 

112.  The  influence  of  Heat  upon  the  vital  activity  of  Animals,  is 
quite  as  strongly  marked  as  we  have  seen  it  to  be  in  the  case  of  Plants ; 
but  the  mode  in  which  it  is  exerted  is  in  many  instances  very  differ- 
ent. In  those  animals  which  are  endowed  with  great  energy  of  mus- 
cular movement,  and  in  which,  for  the  maintenance  of  that  energy,  the 
nutritive  functions  are  kept  in  constant  activity,  we  find  that  a  provi- 


I 


OF  HEAT  AS  A  VITAL  STIMULUS.  81 

sion  exists  for  the  development  of  heat  from  within,  so  as  to  keep  the 
temperature  of  the  body  at  a  certain  uniform  standard,  whatever  may 
be  the  climate  in  which  they  live.  Their  energy  and  activity  are,  in 
fact,  so  dependent  upon  the  steady  maintenance  of  a  high  temperature 
in  their  bodies,  that,  if  this  be  not  kept  up  nearly  to  its  regular  stand- 
ard, a  diminution  or  even  a  complete  cessation  of  vital  action  takes 
place,  and  even  a  total  loss  of  vitality  may  result.  In  these  warm- 
blooded  animals,  as  they  are  termed,  we  do  not  so  evidently  trace  the 
effects  of  Heat,  because  they  are  constantly  being  exerted,  and  because 
external  changes  have  but  little  influence  upon  them,  unless  these 
changes  are  of  an  extreme  kind.  But  if  those  internal  operations,  on 
which  the  maintenance  of  the  temperature  is  dependent,  are,  from  any 
cause,  retarded  or  suspended,  the  effect  is  immediately  visible  in  the 
depressed  activity  of  the  whole  system.  In  the  class  of  Birds  whose 
muscular  energy,  and  whose  general  functional  activity,  are  greater 
and  more  constant  than  those  of  any  other  animals,  the  temperature  is 
pretty  steadily  maintained  at  from  108°  to  112°;  and  we  shall  pre- 
sently see,  that  a  depression  of  the  heat  of  the  body  to  about  80°  is 
fatal.  Among  Mammalia,  the  temperature  is  usually  maintained  at 
from  98°  to  102°;  and  it  seems  that  here,  too,  a  depression  of  about 
thirty  degrees  is  ordinarily  fatal. 

113.  In  the  different  tribes  of  Birds  and  Mammals,  we  find  a  very 
diversified  power  of  generating  heat;  and  on  this  depends  their  adapt- 
ation to  various  climates.  Where  the  usual  temperature  of  the  atmo- 
sphere is  but  little  below  the  normal  standard  ®f  the  body,  a  small 
amount  of  the  internal  calorifying  power  is  required  ;  and  accordingly 
we  find  that  animals  which  naturally  inhabit  the  torrid  zone,  cannot  be 
kept  alive  elsewhere,  except,  like  the  Plants  of  the  same  regions,  by 
external  heat.  On  the  other  hand,  the  animals  of  the  colder-tempe- 
rate and  frigid  climes  are  endowed  with  a  much  greater  internal  calo- 
rifying power;  and  their  covering  is  adapted  to  keep  in  the  heat  which 
they  generate.  Such  animals  (the  Polar  Bear,  for  example,)  cannot  be 
kept  in  health,  in  the  summer  of  our  own  country,  unless  means  are 
taken  for  their  refrigeration.  The  constitution  of  man  seems  to  ac- 
quire, by  habituation  to  a  particular  set  of  conditions  through  succes- 
sive generations,  an  adaptation  to  differences  of  climate,  of  which  that 
of  few  other  animals  is  susceptible ;  and  thus  we  find  different  races 
of  human  beings  inhabiting  countries,  which  are  subject  to  the  ex- 
tremes of  heat  and  cold.  The  Hindoo  or  the  Negro,  suddenly  trans- 
ported to  Labrador  or  Siberia  during  the  depth  of  winter,  would  pro- 
bably sink  in  the  course  of  a  few  days,  from  want  of  power  to  generate 
within  his  body  a  sufficient  amount  of  heat  to  resist  the  depressing  in- 
fluence of  the  external  cold  ;  whilst,  on  the  other  hand,  the  Esquimaux, 
suddenly  conveyed  to  the  hottest  parts  of  India  or  Africa,  would 
speedily  become  the  subject  of  disease,  which  would  probably  terminate 
his  life  in  a  short  time.  It  is  in  the  inhabitant  of  temperate  climates, 
who  is  naturally  exposed  during  the  seasonal  changes  of  his  year,  to  a 
wide  range  of  external  temperature,  that  we  find  the  greatest  power  of 
6 


82  OF  HEAT  AS  A  VITAL  STIMULUS. 

sustaining  the  extremes  of  either  cold  or  heat;  and  yet,  even  in  such, 
the  continued  exposure  to  either  extreme  during  a  long  series  of  years, 
will  so  much  influence  the  heat-producing  power,  that  the  constitu- 
tion does  not  adapt  itself  readily  to  a  change  of  conditions. 

114.  We  see,  then,  that  the  variations  observable  between  different 
races  in  this  respect,  are  only  exaggerations  (so  to  speak)  of  the  alter- 
nations which  an  individual  may  undergo  in  the  course  of  a  few  years; 
and  it  is  easy  to  understand  how  such  an  adaptation  may  take  place  to 
an  increased  extent  in  successive  generations; — this  being  the  regular 
law,  not  merely  in  regard  to  Man,  but  in  regard  to  other  animals 
placed  under  new  conditions,  to  which  they  have  a  certain,  but  limited, 
power  of  adapting  themselves.  Thus  we  find  that  an  European, 
who  has  lived  for  several  years  in  the  East  or  West  Indies,  suffers 
considerably  from  the  cold,  when  he  first  returns  to  \vinter  in  his  na- 
tive country :  his  constitution  having,  for  a  time,  lost  some  of  its  power 
of  generating  heat.  After  a  few  years'  residence,  however,  this  power 
is  commonly  recovered  to  its  original  extent,  unless  the  age  of  the 
individual  be  too  far  advanced;  but  his  children,  if  they  have  been 
not  only  born,  but  brought  up,  in  the  hotter  climate,  experience  much 
greater  difficulty  in  adapting  themselves  to  the  colder  one. 

115.  The  conditions  on  which  the  power  of  maintaining  the  heat 
of  the  body,  in  despite  of  external  cold,  is  dependent,  will  become 
the  subject  of  inquiry  hereafter  (Chap.  X).  It  is  sufficient  here  to 
state,  that  this  power  is  the  result  of  numerous  Chemical  changes 
going  on  within  the  body ;  and  especially  of  a  process  analogous  to 
combustion,  in  which  carbon  and  hydrogen,  taken  in  as  food,  are  made 
to  unite  with  oxygen  derived  from  the  atmosphere.  It  is  dependent, 
therefore,  as  to  its  amount,  upon  the  due  supply  of  the  combustible 
material  on  the  one  hand,  and  of  atmospheric  air  on  the  other.  If  the 
former  is  not  furnished,  either  by  the  food  or  by  the  fatty  matter  of 
the  body,  (which  acts  as  a  kind  of  reserved  store  laid  up  against  the 
time  of  need,)  the  heat  cannot  be  maintained ;  and  it  is  in  part  for 
want  of  power  to  digest  and  assimilate  a  sufficient  amount  of  this 
kind  of  aliment,  that  animals  of  warm  climates  cannot  maintain  their 
temperature  in  colder  regions.  On  the  other  hand,  if  the  supply  of 
oxygen  be  deficient,  as  it  is  when  the  respiration  is  impeded  by- 
diseased  conditions  of  various  kinds,  there  is  a  similar  depression  of 
temperature. 

116.  Now,  if,  from  either  of  these  causes,  the  temperature  of  the 
body  of  a  Bird  or  Mammal  (except  in  the  case  of  the  hyhernating 
species  of  the  latter,  to  be  presently  noticed)  be  lowered  to  about  30° 
below  its  usual  standard,  not  only  is  there  a  cessation  of  vital  activity, 
but  a  total  loss  of  \\\.?\  properties ;  in  other  w^ords,  the  death  of  the 
animal  is  a  necessary  result.  This  occurrence  is  preceded  by  a  gradu- 
ally-increasing torpidity ;  which  shows  the  depressing  influence  of  the 
cooling  process  upon  the  functions  in  general.  The  temperature  of 
the  superficial  parts  of  the  body  is,  of  course,  first  affected ;  the  circu- 
lation is  at  first  retarded,  causing  lividity  of  the  skin ;  but,  as  the  tern- 


OF  HEAT  AS  A  VITAL  STIMULUS.  83 

perature  becomes  lower,  the  blood  is  almost  entirely  expelled  from 
the  surface,  by  the  contraction  of  the  vessels,  and  paleness  succeeds. 
At  the  same  time,  there  is  a  gradually-increasing  torpor  of  the  nervous 
and  muscular  systems,  which  first  manifests  itself  in  an  indisposition 
to  exertion  of  any  kind,  and  then  in  an  almost  irresistible  tendency  to 
sleep.  At  the  same  time,  the  respiratory  movements  become  slower, 
from  the  want  of  the  stimulus  that  should  be  given  by  the  warm  cur- 
rent of  blood  to  the  medulla  oblongata,  which  is  the  centre  of  those 
movements;  and  the  loss  of  heat  goes  on,  therefore,  with  increased 
rapidity,  until  the  temperature  of  the  whole  body  is  so  depressed,  that 
its  vitality  is  altogether  destroyed. 

117.  But  when  there  is  a  deficiency  of  the  proper  animal  heat,  the 
vital  activity  of  the  system  may  be  maintained  by  caloric  supplied  by 
external  sources.  This  fact  is  of  high  scientific  value,  as  giving  the 
most  complete  demonstration  of  the  immediate  dependence  of  the  vital 
functions  of  warm-blooded  animals  upon  a  sustained  temperature ;  and 
its  practical  importance  can  scarcely  be  overrated.  It  rests  chiefly 
upon  the  recent  experiments  of  Chossat,  who  had  in  view  to  determine 
the  circumstances  attending  death  by  Inanition  or  starvation.  He 
found  that,  when  Pigeons  were  entirely  deprived  of  food  and  w^ater, 
their  average  temperature  underwent  a  tolerably  regular  diminution 
from  day  to  day ;  so  that,  after  several  days,  (the  exact  number  vary- 
ing with  their  previous  condition,)  it  was  about  4^°  lower  than  at  first. 
Up  to  this  time,  it  seems  that  the  store  of  fat  laid  up  in  the  body  sup- 
plies the  requisite  material  for  the  combustive  process ;  so  that  no  very 
injurious  depression  of  temperature  occurs.  But,  as  soon  as  this  is 
exhausted,  the  temperature  falls  rapidly,  from  hour  to  hour;  and  as 
soon  as  the  total  depression  has  reached  29^°  or  30°,  death  super- 
venes. Yet  it  was  found  by  M.  Chossat,  that  when  animals  thus 
reduced  by  starvation,  w^hose  death  seemed  impending,  (death  actually 
taking  place,  in  many  instances,  whilst  the  preliminary  processes  of 
weighing,  the  application  of  the  thermometer,  &c.,  were  being  per- 
formed,) were  subjected  to  artificial  heat,  they  were  almost  uniformly 
restored,  from  a  state  of  insensibility  and  want  of  muscular  power,  to 
a  condition  of  comparative  activity.  Their  temperature  rose,  their 
muscular  power  returned,  they  took  food  when  it  was  presented  to 
them,  and  their  secretions  were  renewed  ;  and,  if  this  artificial  assist- 
ance was  sufficiently  prolonged,  and  they  were  supplied  \vith  food, 
they  recovered.  If  the  heat  was  withdrawn,  however,  before  the  time 
when  the  digested  food  was  ready,  in  sufficient  amount,  to  supply  the 
combustive  process,  they  still  sank  for  want  of  it. 

118.  Various  important  practical  hints  may  be  derived  from  the 
consideration  of  these  facts.  There  can  be  no  doubt  that,  in  many 
diseases  of  exhaustion,  the  want  of  power  to  sustain  the  requisite 
temperature,  is  the  immediate  cause  of  death  ;  the  whole  combustible 
material  of  the  body  having  been  exhausted,  and  the  digestive  appa- 
ratus not  being  able  to  supply  what  is  required.  Now  where  this  is 
the  case,  there   is  no  doubt  that   life  may  be   prolonged,  and  that 


84  OF  HEAT  AS  A  VITAL  STIMULUS. 

recovery  may  be  favoured,  by  the  judicious  sustentation  of  the  tem- 
perature of  the  body.  This  may  be  effected  either  by  internal  or  by 
external  means.  Of  the  internal,  the  most  efficient  is  undoubtedly 
the  administration  of  alcoholic  fluids;  which,  for  reasons  hereafter  to 
be  given,  (§  496,)  will  be  absorbed  into  the  circulating  system,  when 
no  other  alimentary  substance  can  be  taken  in;  and  w^hich,  moreover, 
exert  a  favourable  influence  by  their  specific  stimulating  effect  upon 
the  nervous  system.  It  is  a  matter  of  familiar  experience,  that  in 
such  conditions  of  the  body,  the  quantity  of  alcohol  which  may  be 
administered  with  positive  and  evident  benefit,  is  such  as  w^ould  in 
ordinary  circumstances  be  productive  of  the  most  injurious  results; 
and  this  is  fully  accounted  for  by  the  reflection,  that  it  is  burnt  off  as 
fast  as  it  is  taken  in.  But  a  most  important  adjunct  in  all  such  cases, 
— and  in  many  instances  a  substitute  for  alcohol,  when  the  latter 
w^ould  be  inadmissible, — will  be  found  in  the  application  of  external 
heat ;  and  especially  in  the  subjection  of  the  whole  surface  to  its  in- 
fluence, by  means  of  the  hot-air  bath.  This  is  a  valuable  portion  of 
the  treatment,  in  the  recovering  of  persons  who  have  been  reduced 
to  insensibility  by  suffocation  of  any  kind;  and  especially  in  cases  of 

Irowning,  since  the  heat  of  the  body  is  rapidly  withdrawn  by  the 
conducting  power  of  the  water.  Indeed  it  may  be  stated  as  a  general 
rule,  that,  where  the  temperature  of  the  body  is  lowered  from  any 

ause,  external  heat  may  be  advantageously  applied ;  and  much  evi- 
dence has  lately  been  produced  to  show,  that  the  reparative  processes 
by  which  extensive  wounds  are  healed,  go  on  more  favourably  under 
the  contact  of  warm,  dry  air,  than  with  any  other  application. 

119.  On  the  other  hand,  where  the  object  is  to  keep  dow^n  a  ten- 
dency to  a  too  violent  action,  the  local  application  of  moderate  cold 
is  found  to  be  of  the  greatest  value  ;  all  surgeons  of  eminence  being 
now  agreed  upon  the  efficacy  of  water- dressing  in  restraining  the  in- 
flammatory process,  especially  in  cases  of  wounds  of  the  joints,  in 
which  this  action  is  most  to  be  apprehended.  The  general  applica- 
tion of  cold  to  the  surface,  by  means  of  continued  exposure  to  cool 
air,  or  by  a  short  immersion  in  cold  water,  is  frequently  in  the  highest 
degree  beneficial,  by  imparting  tone  to  the  system,  i.e.,  by  producing 
a  firmer  condition  in  the  solids  w^hich  were  previously  relaxed,  and 
more  especially  by  calling  into  action  the  tonicity  of  the  walls  of  the 
blood-vessels,  wdiich  imparts  to  them  an  increased  resistance,  and  thus 
favours  the  regular  and  vigorous  circulation  of  blood,  upon  principles 
which  will  be  hereafter  stated  (§  609).  But  so  far  from  producing 
any  permanent  depression  in  the  temperature  of  the  body,  this  mea- 
sure has  a  tendency  to  elevate  it,  by  the  increased  vigour  it  produces 
in  the  circulation  ;  hence  the  glow  which  is  experienced  after  the 
use  of  the  cold  bath.  If  this  effect  be  not  produced,  and  a  chilling 
of  the  body,  instead  of  an  invigorating  warmth,  be  the  result  of  the 
use  of  cold,  it  is  evident  that  this  cannot  be  beneficial.  The  inju- 
rious results  of  the  too-prolonged  application  of  even  a  moderate 
degree  of  cold,  are  seen  in  the  depression  of  temperature,  without  a 


OF  HEAT  AS  A  VITAL  STIMULUS.  S& 

corresponding  reaction,  which  is  the  consequence  of  an  immersion  in 
water  of  50°  or  55°  prolonged  for  several  hours  ;  and  still  more  in 
that  chilling  of  the  whole  surface  frequently  productive  of  the  most 
serious  consequences,  which  arises  from  the  evaporation  of  fluid  from 
garments  that  have  been  moistened,  either  by  perspiration  from  with- 
in, or  by  the  fall  of  rain  or  dew  upon  their  exterior.  There  is  no 
doubt  that  the  obstruction  to  the  continuance  of  the  perspiration, 
presented  by  a  covering  already  saturated  with  moisture,  is  one  cause 
of  the  injurious  results  that  so  commonly  follow  such  an  occurrence; 
but  there  is  as  little  doubt  that  the  chilling  influence  of  the  external 
evaporation  has  a  large  share  in  producing  them.  For  experience 
shows  that,  if  the  evaporation  be  prevented  by  an  impenetrable 
covering,  the  contact  of  a  garment  thoroughly  saturated  with  mois- 
ture is  not  productive  of  the  same  injurious  consequences. 

120.  The  practical  importance  of  the  due  comprehension  of  the 
principles  upon  which  heat  and  cold  should  be  employed,  in  the 
treatment  of  disease  and  the  preservation  of  health,  has  required 
this  digression.  We  now  proceed  to  consider  the  influence  of 
temperature  upon  a  certain  group  of  warm-blooded  animals  ;  which 
offers  a  remarkable  peculiarity  in  this  respect, — their  power  of  gene- 
rating heat  being  for  a  time  greatly  diminished  or  almost  completely 
suspended  ;  the  temperature  of  their  bodies  following  that  of  the 
air  around,  so  that  it  may  be  brought  down  nearly  to  the  freezing- 
point  ;  their  general  vital  actions  being  carried  on  with  such  feeble- 
ness as  to  be  scarcely  perceptible  ;  and  yet  the  vital  properties  of 
the  tissues  being  retained,  so  that,  when  the  temperature  of  the  body 
is  again  raised,  the  usual  activity  returns.  This  state,  which  is 
called  hybernation,  appears  to  be  as  natural  to  certain  animals,  as 
sleep  is  to  all ;  and  it  corresponds  with  sleep  in  its  tendency  to 
periodical  return. 

121.  No  account  can  be  given  of  the  causes  to  which  it  is  due; 
but  the  condition  of  the  animals  presenting  it  offers  several  points  of 
much  interest.  There  are  some,  as  the  Lagomys,  in  which  it  appears 
to  differ  but  little  from  deep  ordinary  sleep  ;  they  retire  into  situations 
which  favour  the  retention  of  their  warmth  ;  and  they  occasionally 
wake  up,  and  apply  themselves  to  some  of  the  store  of  food,  which 
they  have  provided  in  the  autumn.  In  other  cases,  a  great  accumu- 
lation of  fat  takes  place  within  the  body  in  autumn,  favoured  by  the 
oily  nature  of  the  seeds,  nuts,  &c.,  on  which  the  animals  then  feed  ; 
and  this  serves  the  purpose  of  maintaining  the  temperature  for  a  suf- 
ficient length  of  time,  not  indeed  to  the  usual  standard,  but  to  one 
not  far  below  it.  The  state  of  torpor  in  these  animals  is  more  pro- 
found than  that  of  deep  sleep,  but  it  is  not  such  as  to  prevent  them 
from  being  easily  aroused  ;  and  their  respiratory  movements,  though 
diminished  in  frequency,  are  still  performed  without  interruption. 
But  in  the  Marmot,  and  in  animals  which,  like  it,  hybernate  com- 
pletely, the  temperature  of  the  body  (owing  to  the  want  of  internal 
power  to  generate  heat)  and  the  general  vital  activity,  are  proper- 


86  OF  HEAT  AS  A  VITAL  STIMULUS. 

tionably  depressed ;  the  respiratory  movements  fall  from  500  to  14 
per  hour,  and  are  performed  without  any  considerable  enlargement  of 
chest  ;  the  pulse  sinks  from  150  to  15  beats  per  minute  ;  the  state 
of  torpidity  is  so  profound  that  the  animal  is  with  difficulty  aroused 
from  it ;  and  the  heat  of  the  body  is  almost  entirely  dependent  upon 
the  temperature  of  the  surrounding  air,  not  being  usually  more  than 
a  degree  or  two  above  it.  When  the  thermometer  in  the  air  is 
somewhat  below  the  freezing-point,  that  placed  within  the  body  falls 
to  about  35° ;  and  at  this  point  it  may  remain  for  some  time  without 
any  apparent  injury  to  the  animal,  as  it  revives  when  subjected  to  a 
higher  temperature.  When,  however,  the  body  is  exposed  to  a  more 
intense  degree  of  cold,  the  animal  functions  undergo  a  temporary  re- 
newal ;  for  the  cold  seems  to  act  like  any  other  stimulus  in  arousing 
them.  The  respiratory  movements  and  the  circulation  increase  in  ac- 
tivity, so  as  to  generate  an  increased  amount  of  heat ;  but  this  amount 
is  insufficient  to  keep  up  the  temperature  of  the  body,  which  is  at  last 
depressed  to  a  degree  inconsistent  with  the  maintenance  of  life  ;  and 
not  only  the  suspension  of  activity,  but  the  total  loss  of  vital  proper- 
ties is  the  result. 

122.  Now  the  condition  of  a  hybernating  Mammal  closely  resem- 
bles that  of  a  cold-blooded  animal,  in  regard  to  the  dependence  of  its 
bodily  temperature  upon  external  conditions.  There  is  this  important 
difference,  however ; — that  the  reduction  of  the  temperature  of  the 
former  to  60*^  or  50°  is  incompatible  with  a  state  of  activity,  which 
is  only  exhibited  when  the  temperature  rises  to  nearly  the  usual  Mam- 
malian standard  ; — whilst  a  permanently  low  or  moderate  temperature 
is  natural  to  the  bodies  of  most  cold-blooded  animals,  whose  func- 
tions could  not  be  well  carried  on  under  a  higher  temperature.  Thus 
all  the  muscles  of  a  Frog  are  thrown  into  a  state  of  permanent  and 
rigid  contraction,  by  the  immersion  of  its  body  in  water  no  warmer 
than  the  blood  which  naturally  bathes  those  of  the  Bird  ;  and  we  find, 
accordingly,  that  cold-blooded  animals  which  cannot  sustain  a  high 
temperature,  are  provided  with  2i  frigorifying  rather  than  with  a  calo- 
rifying  apparatus.  Although  we  are  accustomed  to  rank  all  animals, 
save  Birds  and  Mammals,  under  the  general  term  cold-blooded,  yet 
there  exist  among  them  considerable  diversities  as  to  the  power  of 
generating  heat  within  themselves,  and  of  thus  rendering  themselves 
independent  of  external  variations.  Thus  among  Reptiles,  it  appears 
that  there  are  some  which  can  sustain  a  temperature  several  degrees 
above  that  of  the  atmosphere,  especially  when  the  latter  is  sinking ; 
and  among  Fishes  it  is  certain  that  there  are  species, — the  Tunny  and 
Bonifo,  for  example, — which  are  almost  entitled  to  the  name  of  warm- 
blooded animals,  their  temperature  being  kept  up  to  nearly  100°, 
when  that  of  the  sea  is  about  80°.  It  is  uncertain,  however,  to  what 
extent  it  would  be  depressed,  by  a  lowering  of  that  of  the  surround- 
ing medium.  The  greatest  power  of  developing  heat  in  cold-blooded 
animals  appears  to  exist,  when  their  bodies  are  reduced  nearly  to  the 
freezing-point,  and  when  that  of  the  surrounding  air  or  water  is  much 


OF  HEAT  AS  A  VITAL  STIMULUS.  87 

below  it.  Thus  Frogs  have  been  found  alive  in  the  midst  of  ice 
whose  temperature  was  as  low  as  9°,  the  heat  of  their  own  bodies 
being  33° ;  and  it  has  been  observed  that  even  Animalcules  contained 
in  water  that  is  being  frozen,  are  not  at  once  destroyed,  but  that  each 
lives  for  a  time  in  a  small  uncongealed  space,  where  the  fluid  seems 
to  be  kept  from  solidifying  by  the  caloric  liberated  from  the  Animal- 
cule. 

123.  The  peculiar  condition  of  the  class  of  Insects,  in  regard  to  its 
heat-producing  power,  exhibits  in  a  very  striking  manner  the  con- 
nection between  an  elevated  temperature  and  vital  activity.  In  the 
Larva  state  of  Insects,  the  temperature  of  the  animal  follows  closely 
that  of  the  surrounding  air,  as  in  the  cold-blooded  classes  generally ; 
but  it  is  usally  from  \^  to  4°  above  it.  In  the  Pupa  condition,  which 
is  one  of  absolute  rest  in  all  insects  that  undergo  a  complete  meta- 
morphosis, the  temperature  scarcely  rises  above  that  of  the  surround- 
ing medium  ;  except  nearly  at  the  close  of  the  period,  when  it  is 
about  to  burst  its  envelops  and  to  come  forth  as  the  perfect  Insect. 
The  elevation  of  temperature  which  different  Insects  present,  varies 
in  part  according  to  the  species,  and  in  part  with  the  condition  of  the 
individual  in  regard  to  rest  or  activity  ;  but  the  same  principle  is  evi- 
dently operating  in  both  cases,  since  the  variation  existing  amongst 
diflferent  species,  in  regard  to  their  heat-producing  power,  is  closely 
connected  with  the  amount  of  activity  natural  to  them.  The  highest 
amount  is  to  be  found  in  the  industrious  Hive-Bee  and  its  allies,  and 
in  the  elegant  and  sportive  Butterflies,  which  are  almost  constantly  on 
the  wing  in  search  of  food ;  next  to  these  come  the  Beetles  of  active 
flight ;  and  lastly  those  which  seldom  or  never  raise  themselves  upon 
the  wing,  but  pursue  their  labours  on  the  ground.  The  temperature 
of  individual  Bees  has  been  found  to  be  about  4°  above  that  of  the 
atmosphere,  when  they  are  in  a  state  of  repose  ;  but  it  rises  to  10°  or 
15°  when  they  are  excited  to  activity.  When  they  are  aggregated 
together  in  clusters,  however,  the  temperature  which  they  possess  is 
often  as  much  as  40°  above  that  of  the  atmosphere.  When  reduced 
to  torpidity  by  cold,  they  still  generate  heat  enough  to  keep  them  from 
being  frozen,  unless  the  cold  be  very  severe  ;  and  they  may  be 
aroused  by  moderate  excitement  to  a  state  of  activity,  in  which  the 
temperature  rises  to  a  very  considerable  height.  Now  although  the 
increased  production  of  heat  is  in  these  cases,  as  in  hybernating  Mam- 
mals, similarly  aroused,  the  consequence  of  the  increased  activity,  there 
can  be  no  question  that  it  is  a  condition  necessary  to  the  continuance 
of  that  activity  ;  since  we  find  that,  if  the  temperature  of  the  body  be 
again  reduced  by  external  cold,  the  activity  cannot  be  long  main- 
tained. 

124.  Whilst  the  foregoing  facts  exhibit  the  connection  between  an 
elevated  temperature,  and  the  most  active  condition  of  the  muscular 
and  nervous  systems,  in  cold-blooded  animals,  there  is  abundant  evi- 
dence of  the  same  kind  in  regard  to  the  influence  of  heat  upon  the 
processes  of  nutrition  and  development.     Thus  the  time  of  emersion 


88  OF  HEAT  AS  A  VITAL  STIMULUS. 

of  Insect-larvse  from  their  eggs, — or  in  other  words,  the  rate  at  which 
the  previous  formative  processes  go  on,  is  entirely  dependent  upon 
the  temperature.  In  the  case  of  the  Bird  we  find  that,  if  the  tempe- 
rature be  not  sufficient  to  develop  the  egg,  chemical  changes  soon 
take  place,  which  involve  the  loss  of  its  vitality  ;  or  if  the  tempera- 
ture be  reduced  so  low  as  to  prevent  the  occurrence  of  those  changes, 
the  loss  of  heat  is  in  itself  destructive  of  life.  But  this  is  not  the  case 
in  regard  to  the  eggs  of  cold-blooded  animals  in  general ;  for,  like  the 
beings  they  are  destined  to  produce,  they  may  be  reduced  to  a  state 
of  complete  inaction  by  a  depression  of  the  external  temperature  ; 
whilst  a  slight  elevation  of  this  renews  their  vital  operations,  at  a  rate 
corresponding  to  the  warmth  supplied.  Hence  the  production  of  lar- 
vae from  the  eggs  of  Insects  may  be  accelerated  or  retarded  at  plea- 
sure ;  and  this  is,  in  fact,  practised  in  the  rearing  of  Silk-worms,  in 
order  to  adapt  the  time  of  their  emersion  from  the  egg  to  the  supply 
of  food  which  is  ready  for  them.  The  same  may  be  said  in  regard  to 
the  eggs  of  other  cold-blooded  animals;  those,  for  example,  of  the 
minute  Entomostracous  Crustacea  (Water-Fleas,  &c.,)  which  people 
our  ditches  and  ponds.  In  many  of  these,  the  race  is  continued 
solely  by  the  eggs,  which  remain  dormant  through  the  winter  ;  all  the 
parents  being  destroyed  by  the  cold.  The  common  Daphnia  pulex 
produces  two  kinds  of  eggs;  from  one,  the  young  are  very  speedily 
hatched:  but  the  others,  which  are  produced  in  the  autumn,  and  en- 
veloped in  a  peculiar  covering,  do  not  give  birth  to  the  contained 
young  until  the  succeeding  spring.  They  may  be  at  any  time  hatched, 
however,  by  artificial  warmth. 

125.  We  sometimes  find  special  provisions,  for  imparting  to  the 
eggs  a  temperature  beyond  that  which  is  natural  to  the  bodies  of  the 
parents;  thus  it  has  been  lately  shown  that  in  Serpents,  the  tempera- 
ture of  the  posterior  part  of  the  body  rises  considerably,  when  the 
eggs  are  lying  in  the  oviduct,  preparatory  to  being  discharged, — 
evidencing  a  special  heat-producing  power  in  the  surrounding  parts 
at  this  period,  which  is  obviously  for  the  purpose  of  aiding  the  matu- 
rity of  the  eggs.  The  Viper,  whose  eggs  are  frequently  hatched  in 
the  maternal  oviduct,  so  that  the  young  are  brought  forth  alive,  is 
occasionally  seen  basking  in  the  sun,  in  such  a  position  as  to  receive 
its  strongest  heat  on  the  parts  that  coverthe  oviduct.  Certain  Birds 
have  recourse  to  substitutes  for  the  usual  method  of  incubation.  The 
Tallegalla  of  New  Holland  is  directed  by  its  remarkable  instinct,  not 
to  sit  upon  its  eggs,  but  to  bring  them  to  maturity  by  depositing  them 
in  a  sort  of  hot-bed,  which  it  constructs  of  decaying  vegetable  matter. 
The  Ostrich  is  believed  to  sit  upon  its  eggs,  when  the  temperature  falls 
below  a  certain  standard,  but  to  leave  them  to  the  influence  of  the  solar 
heat  when  this  is  sufficient  to  bring  them  to  maturity;  and  this  state- 
ment derives  confirmation  from  a  similar  fact  observed  in  a  Fly- 
catcher, which  built  in  a  hot-house  during  several  successive  years, 
— the  bird  quitting  its  eggs  when  the  temperature  w,as  high,  and 
resuming  its  place  when  it  fell.     In  all  these  cases,  as  in  many  more 


OF  HEAT  AS  A  VITAL  STIMULUS.  89 

which  might  be  enumerated,  we  observe  the  influence  of  an  elevated 
temperature  upon  the  processes  of  development;  and  the  provisions 
made  by  Nature,  in  the  physical  or  mental  constitution  of  animals, 
for  affording  that  influence.  The  development  of  heat  around  the 
oviduct  of  the  Serpent  is  a  process  over  which  the  individual  has 
no  control,  being  entirely  dependent  upon  certain  Organic  changes; 
whilst  the  imparting  of  warmth  to  its  eggs  by  the  Bird,  either  from 
its  own  body  or  through  artificial  means,  is  committed  to  the  guidance 
of  its  Instinct, — which  same  instinct  leads  it  to  suspend  the  process 
when  it  is  not  necessary. 

126.  Phenomena  of  an  equally  interesting  and  instructive  charac- 
ter may  be  observed  in  the  history  of  the  Pupa  state  of  Insects ;  which, 
in  those  that  undergo  a  complete  metamorphosis,  may  be  almost  cha- 
racterized as  a  re-entrance  into  the  egg.  In  fact  we  shall  obtain  the 
most  correct  idea  of  the  nature  of  that  metamorphosis,  by  considering 
the  Larva  as  an  embryo,  which  comes  forth  from  the  egg  in  a  very 
early  and  undeveloped  condition,  for  the  sake  of  obtaining  materials 
for  its  continued  development,  which  the  egg  does  not  supply  in 
sufficient  amount.  When  these  have  been  digested  and  stored  up  in 
the  body,  the  animal  becomes  completely  inactive,  so  far  as  regards 
its  external  manifestations  of  life  ;  and  it  forms  some  kind  of  envelop 
for  its  protection,  which  may  not  be  unaptly  compared  to  the  shell  or 
horny  covering  of  the  egg.  Within  this  are  gradually  developed  the 
wings,  legs,  and  other  parts  which  are  peculiar  to  the  perfect  Insect ; 
whilst  even  those  organs,  which  it  possesses  in  common  with  the 
Larva,  are  for  the  most  part  completely  altered  in  character.  When 
this  process  of  development  is  completed,  the  Insect  emerges  from 
its  Pupa  case,  just  as  the  Bird  comes  forth  from  the  egg ;  then  only 
does  its  Insect  life  begin,  its  previous  condition  having  been  that  of 
a  Worm;  and  the  alteration  of  its  character  is  just  as  evident  in  its 
instinctive  propensities,  as  it  is  in  its  locomotive  and  sensorial  powers. 

127.  Now  this  process  of  development  is  remarkably  influenced 
by  external  temperature  ;  being  accelerated  by  genial  warmth,  and 
retarded  by  cold.  There  are  many  Larvae,  which  naturally  pass  into 
the  Pupa  state  during  the  autumn,  remain  in  it  during  the  entire 
winter,  and  emerge  as  perfect  Insects  with  the  return  of  spring.  It 
was  found  by  Reaumur,  that  Pupse,  which  would  not  naturally  have 
been  disclosed  until  May,  might  be  caused  to  undergo  their  meta- 
morphosis during  the  depth  of  winter,  by  the  influence  of  artificial 
heat ;  whilst,  on  the  other  hand,  their  change  might  be  delayed  a 
whole  year  beyond  its  usual  time,  by  the  prolonged  influence  of  a 
cold  atmosphere.  In  order  to  hasten  the  development  of  the  pupse 
of  the  Social  Bees,  a  very  curious  provision  is  made.  There  is  a 
certain  set,  to  which  the  name  of  Nurse-bees  has  been  given,  whose 
duty  it  is  to  cluster  over  the  cells  in  which  the  Nymphs  or  Pupse  are 
lying,  and  to  communicate  the  heat  to  them,  which  is  developed  by 
the  energetic  movements  of  their  own  bodies,  and  especially  by  respi- 
ratory actions  of  extreme  rapidity.     The  nurse-bees  begin  to  crowd 


90  OF  HEAT  AS  A  VITAL  STIMULUS. 

upon  the  cells  of  the  nymphs,  about  ten  or  twelve  hours  before  these 
last  come  forth  as  perfect  Bees.  The  incubation  (for  so  it  may  be 
called)  is  very  assiduously  persevered  in  during  this  period  by  the 
Nurse-bees ;  when  one  quits  the  cell,  another  takes  its  place ;  and 
the  rapidity  of  the  respiratory  movements  increases,  until  they  rise  to 
130  or  140  per  minute,  so  as  to  generate  the  greatest  amount  of 
heat  just  before  the  young  bees  are  liberated  from  the  combs.  In 
one  instance,  the  thermometer  introduced  among  seven  nursing-bees 
stood  at  92^° ;  the  temperature  of  the  external  air  being  70°.  We 
observe  in  this  curious  propensity  a  manifest  provision  for  accelera- 
ting the  development  of  the  perfect  Insect,  which  requires  (as  already 
pointed  out)  a  higher  temperature  than  the  larva,  in  virtue  of  its 
greater  activity.  The  Nurse-bees  do  not  station  themselves  over  the 
cells  which  are  occupied  by  the  larvae ;  nor  do  they  incubate  the 
nymph-cells  with  any  degree  of  constancy  and  regularity,  until  the 
process  of  development  is  approaching  its  highest  point. 

128.  We  have  seen  that  the  animals  termed  cold-blooded  are 
greatly  influenced  as  to  the  temperature  of  their  bodies,  by  the  tem- 
perature of  the  surrounding  medium  ;  although  many  of  them  are 
endowed  with  the  power  of  keeping  themselves  a  certain  number  of 
degrees  above  it.  Now  the  consequence  of  this  is,  that  all  of  them 
which  are  subject  to  any  considerable  and  prolonged  amount  of  cold, 
pass  into  a  state  of  more  or  less  complete  inactivity  during  its  con- 
tinuance ;  which  state  bears  a  close  correspondence  with  the  hyber- 
nation of  certain  Mammalia.  Among  the  Reptiles  of  cold  and  tem- 
perate countries,  this  torpid  state  uniformly  occupies  a  considerable 
part  of  the  year ;  as  it  does  also  with  Insects,  terrestrial  Mollusks, 
and  other  Invertebrated  animals,  which  are  subject  to  the  influence 
of  the  cold.  On  the  other  hand.  Fishes,  Crustacea,  and  other  ma- 
rine animals,  do  not  usually  appear  to  pass  into  a  state  of  torpidity; 
the  temperature  of  the  medium  they  inhabit  never  undergoing  a 
degree  of  depression  nearly  so  great  as  that  of  the  atmosphere. 
The  amount  of  change  necessary  to  produce  this  effect,  or  on  the 
other  hand  to  call  the  animals  from  a  state  of  torpidity  to  one  of 
active  energy,  differs  for  different  species  ;  and  there  is  probably  a 
considerable  difference  even  among  individuals  of  the  same  species, 
according  to  the  temperature*under  which  they  habitually  live.  Thus 
one  animal  may  remain  torpid  under  a  degree  of  warmth  which  will 
be  sufficient  to  arouse  another  of  the  same  kind  accustomed  to  a 
somewhat  colder  climate  ;  because  the  stimulus  is  relatively  greater  to 
the  latter. 

129.  It  was  observed  by  Mr.  Darwin,  that  at  Bahia  Blanca,  in 
South  America,  the  first  appearance  of  activity  in  animal  and  vegeta- 
ble life,  a  few  days  before  the  vernal  equinox,  presented  itself  under 
a  mean  temperature  of  58°,  the  range  of  the  thermometer  in  the 
middle  of  the  day  being  between  60°  and  70°.  The  plains  were 
ornamented  by  the  flowers  of  a  pink  wood-sorrel,  wild  peas,  evening 
primroses,  and  geraniums ;  the  birds  began  to  lay  their  eggs,  numer- 


OF  HEAT  AS  A  VITAL  STIMULUS.  91 

ous  beetles  were  crawling  about ;  and  lizards,  the  constant  inhabit- 
ants of  a  sandy  soil,  were  darting  about  in  every  direction.  Yet  a 
few  days  previously,  it  seemed  as  if  nature  had  scarcely  granted  a 
living  creature  to  this  dry  and  arid  country;  and  it  was  only  by  dig- 
ging in  the  ground  that  their  existence  had  been  discovered, — several 
insects,  large  spiders,  and  lizards,  having  been  found  in  a  half  torpid 
state.  Now  at  Monte  Video,  four  degrees  nearer  the  Equator,  the 
mean  temperature  had  been  above  58°  for  some  time  previously,  and 
the  thermometer  rose  occasionally  during  the  middle  of  the  day,  to 
69°  or  70° ;  yet  with  this  elevated  temperature,  almost  equivalent 
to  the  full  summer  heat  of  our  own  country,  almost  every  beetle, 
several  genera  of  spiders,  snails,  and  land-shells,  toads  and  lizards, 
were  still  lying  torpid  beneath  stones.  We  have  seen  that  at  Bahia 
Blanca,  whose  climate  is  but  a  little  colder,  this  same  temperature, 
with  a  rather  less  extreme  heat,  was  sufficient  to  awake  all  orders  of 
animated  beings; — showing  how  nicely  the  required  degree  of  stimu- 
lus is  adapted  to  the  general  climate  of  the  place,  and  how  little  it 
depends  on  absolute  temperature. 

130.  We  may  learn  much  from  the  Geographical  distribution  of 
the  different  species  of  cold-blooded  animals,  in  regard  to  the  influence 
of  temperature  on  Animal  life.  No  general  inferences  of  this  kind 
can  be  founded  upon  the  distribution  of  warm-blooded  animals  ;  since'' 
their  own  heat-evolving  powers  make  them  in  great  degree  inde- 
pendent of  external  warmth.  And  it  is  probably  from  the  distribu- 
tion of  the  marine  tribes,  whose  extension  is  less  influenced  by  local 
peculiarities,  that  the  most  satisfactory  deductions  are  to  be  drawn. 
In  regard  to  the  class  of  Crustacea,  which  is  the  one  that  has  been 
most  fully  investigated  in  this  respect,  the  following  principles  have 
been  pointed  out  by  M.  Milne  Edwards ;  and  they  are  probably  more 
or  less  applicable  to  most  others. 

I.  The  varieties  of  form  and  organization  manifest  themselves  more, 
in  proportion  as  we  pass  from  the  Polar  Seas  towards  the  Equator. — 
Thus  on  the  coast  of  Norway,  where  there  is  frequently  a  vast  multi- 
plication of  individuals  of  the  same  species,  the  number  of  species  is 
very  small  ;  but  the  latter  increases  rapidly  as  we  go  southwards. 
Thus  the  number  of  species  of  Crustacea  of  the  two  highest  Orders, 
known  to  exist  on  the  coast  of  Norway  and  in  the  neighbouring 
seas,  is  only  16  ;  but  82  are  known  to  be  the  inhabitants  of  the  wes- 
tern shores  of  Britain,  France,  Spain,  and  Portugal;  114  are  known 
in  the  Mediterranean  Sea  ;  and  202  in  the  Indian  Ocean.  A  similar 
increase  may  be  observed  in  following  the  coast  of  the  New  World, 
from  Greenland  to  the  Caribbean  Sea. 

II.  The  differences  of  form  and  organization  are  not  only  more  nu- 
merous and  more  characteristic  in  the  warm  than  in  the  cold  regions  of 
the  globe;  they  are  also  more  important. — The  number  of  natural 
groups,  which  we  find  represented  in  the  polar  and  temperate  re- 
gions, is  much  smaller  than  that,  of  which  we  find  types  or  examples 
in  the  tropical  seas.     In  fact,  nearly  all  the  principal  forms  which 


92-  OF  HEAT  AS  A  VITAL  STIMULUS. 

are  met  with  in  colder  regions,  also  present  themselves  in  warm  ;  but 
a  very  large  proportion  of  the  latter  have  no  representatives  among 
the  former.  Of  the  three  primary  groups  composing  the  Class,  in- 
deed, one  is  altogether  wanting  beyond  the  44th  degree  of  latitude  ; 
and  in  the  other  two  there  are  whole  Orders,  as  well  as  numerous 
subordinate  divisions,  which  are  as  completely  restricted  to  the  war- 
mer seas. 

III.  JYot  only  are  those  Crustacea^  which  are  most  elevated  in  the 
scale^  deficient  in  the  Polar  regions  ;  but  their  relative  number  increases 
rapidly  as  we  pass  from  the  Pole  towards  the  Equator. — Thus  the 
Brachyoura,*^  which  must  be  considered  as  the  most  elevated  of  the 
whole  series,  are  totally  absent  in  some  parts  of  the  arctic  region  ;  and 
we  find  their  place  tak;en  by  the  far  less  complete  Edriophthalma, 
with  a  small  number  of  Anomourous  and  Macrourous  Decapods.  In 
the  Mediterranean,  however,  the  Decapods  surpass  the  Edriophthal- 
ma in  regard  to  the  number  of  species;  and  the  Brachyourous  division 
of  the  former  predominates  over  the  Macrourous,  in  the  proportion 
of  two  to  one.  And  in  the  East  and  West  Indies,  the  species  of 
Brachyoura  are  to  those  of  Macroura,  as  three,  four,  or  even  five,  to 
one.  Again,  the  Land  Crabs,  which  are  probably  to  be  regarded  as 
taking  the  highest  rank  among  the  Brachyoura  (and  therefore  in  the 
entire  class),  are  only  to  be  met  with  between  the  tropics.  Moreover, 
of  the  fluviatile  Decapods  (inhabiting  rivers,  brooks,  and  fresh-water 
lakes,)  a  large  proportion  belong,  in  tropical  regions,  to  the  elevated 
type  of  the  Brachyoura  ;  whilst  all  those  found  in  the  temperate  and 
arctic  zones  (the  River  Cray-fish  and  its  allies)  belong  to  the  Macrou- 
rous division. 

IV.  When  we  compare  together  the  Crustacea  of  different  parts  of 
the  world,  we  observe  that  the  average  size  of  these  animals  is  consider- 
ably greater  in  tropical  regions,  than  in  the  temperate  or  frigid  climes. — 
The  largest  species  of  the  arctic  and  antarctic  seas  are  far  smaller  than 
those  of  the  tropical  ocean  ;  and  they  bear  a  much  smaller  proportion 
to  the  whole  number.  Further,  in  almost  every  natural  group,  we 
find  that  the  largest  species  belong  to  the  equatorial  regions;  and  that 
those  which  represent  them  (or  take  their  place,  as  it  were,)  in  tempe- 
rate regions,  are  of  smaller  dimensions. 

V.  It  is  where  the  species  are  most  numerous  and  varied,  and  where 
they  attain  the  greatest  size,  in  other  words,  where  the  temperature  is 
most  elevated, — that  the  peculiarities  of  structure  which  characterize  the 
several  groups  are  most  strongly  manifested.  Thus  the  transverse  de- 
velopment of  the  cephalo-thorax,  which  is  so  remarkable  in  the  Bra- 
chyourous Decapods  (the  breadth  of  the  carapace  or  arched  shell  in  the 
typical  Crabs  being  much  greater  than  its  length  from  back  to  front),  is 
carried  to  its  greatest  extent  in  certain  Crustacea  of  the  Equatorial  re- 

*  The  DECAronA  or  ten-footed  Crustaceans  constitute  the  highest  or  most  perfectly 
organized  Order  of  the  class.  This  Order  is  composed  of  the  Brachyoura  (short- 
tailed)  or  Crabs;  of  the  Macroura  (long-tailed)  or  Lobsters,  Shrimps,  &c.;  and  of  the 
Anonioura  (dissimilar-tailed)  or  Hermit-Crabs,  &c. 


OF  HEAT  AS  A  VITAL  STIMULUS.  93 


gion ;  and  the  same  might  be  said  of  the  characteristic  peculiarities  of 
most  other  natural  groups.  Further,  it  is  in  this  region  that  we  find 
the  greatest  number  of  those  anomalous  forms,  which  depart  most 
widely  from  the  general  structure  of  the  Class. 

VI.  Lastly,  there  is  a  remarkable  coincidence  between  the  temperature 
of  different  regions,  and  the  prevalence  of  certain  forms  of  Crustacea. — 
Thus  there  are  few  genera  to  be  met  with  in  the  West  Indian  seas 
which  have  not  their  representatives  in  the  East  Indian, — the  species, 
however,  being  usually  different.  The  same  may  be  said  of  the  genera 
inhabiting  the  temperate  regions  of  the  globe  ; — similar  generic  forms 
being  usually  met  with  in  the  corresponding  parts  of  the  Old  and  New 
World,  and  of  the  Northern  and  Southern  Hemispheres,  although  the 
species  are  almost  invariably  different. 

131.  Now  although,  as  appears  from  the  foregoing  general  state- 
ments, the  number  of  species  of  Crustacea  inhabiting  the  colder  seas 
bears  a  very  small  proportion  to  that  which  is  found  within  the  tro- 
pics, and  although  the  species  formed  to  inhabit  cold  climates  are  so 
far  inferio-r,  both  as  to  size  and  as  to  perfection  of  development,  yet  it 
does  not  follow  that  the  same  proportion  exists  in  regard  to  the  rela- 
tive amount  of  Crustacean  life  in  the  two  regions:  for  this  depends 
upon  the  multiplication  of  individuals.  In  fact  it  may  be  questioned 
whether  there  is  any  inferiority  in  this  respect;  so  abundant  are  some 
of  the  smaller  species  in  the  Arctic  and  Antarctic,  as  well  as  in  the 
Temperate  seas.  Thus  we  see  that  a  low  range  of  temperature  is  as 
well  adapted  to  sustain  their  life,  as  a  higher  range  is  to  call  forth  those 
larger  and  more  fully  developed  forms,  which  abound  in  the  tropical 
ocean.  This  is  an  obvious  reason  why  the  seas  of  the  frigid  zones 
should  be  much  more  abundantly  peopled  than  the  land;  the  mean 
temperature  of  the  former  being  much  higher.  And  it  would  almost 
seem  as  if  Nature  had  intended  to  compensate  for  the  dreariness  and 
desolation  of  the  one,  by  the  profuseness  of  life  which  she  has  fitted 
the  other  to  support. 

132.  The  influence  of  Temperature  in  modifying  the  size  of  indi- 
vidual Animals  of  the  same  species,  is  not  so  strongly  marked  as  it  is 
in  the  case  of  Plants;  for  this  reason,  perhaps,  that  an  amount  of  con- 
tinued depression  or  elevation,  which  might  be  sustained  by  a  Plant, 
but  which  w^ould  exert  a  modifying  influence  upon  its  growth,  would 
be  fatal  to  an  animal  formed  to  exist  in  the  same  climate.  Instances  are 
not  w^anting,  however,  in  which  such  a  modifying  influence  is  evident; 
and  these,  as  might  be  anticipated,  are  to  be  met  with  chiefly  among 
the  cold-blooded  tribes.  Thus  the  Bulimus  rosaceus,  a  terrestrial  Mol- 
lusk,  is  found  on  the  mountains  of  Chili  of  so  much  less  a  size  than 
that  which  it  attains  on  the  coast,  as  to  have  been  described  as  a  dis- 
tinct species.  And  the  Littorina  petraa,  found  on  the  south  side  of 
Plymouth  Breakwater,  acquires,  from  its  superior  exposure  to  light 
and  heat  (though,  perhaps,  also  from  the  greater  supply  of  nutriment 
which  it  obtains),  twice  the  size  common  to  individuals  living  on  the 
north  side  within  the  harbour.    The  following  circumstance  show^sthe 


94          '  OF  HEAT  AS  A  VITAL  STIMULUS. 

favourable  influence  of  an  elevated  temperature,  in  producing  an  un- 
usual prolificness  in  Fish ;  which  must  be  connected  with  general  vital 
activity.  Three  pairs  of  Gold-fish  were  placed,  some  years  since,  in 
one  of  the  engine-dams  or  ponds  common  in  the  manufacturing  dis- 
tricts, into  which  the  water  from  the  engine  is  conveyed  for  the  pur- 
pose of  being  cooled;  the  average  temperature  of  such  dams  is  about 
80°.  At  the  end  of  three  years  the  progeny  of  these  Fish,  which 
were  accidentally  poisoned  by  verdigris  mixed  with  the  refuse  tallow 
from  the  engine,  were  taken  out  by  wheelbarrows-full.  It  is  not 
improbable  that  the  unusual  supply  of  aliment,  furnished  by  the  re- 
fuse grease  that  floats  upon  these  ponds  (which  would  impede  the 
cooling  of  the  water,  if  it  w^ere  not  consumed  by  the  Fish),  contri- 
buted w^ith  the  high  temperature  to  this  unusual  fecundity. 

133.  The  influence  of  variations  in  the  Heat  of  the  body  upon  its 
vital  activity,  is  further  manifested  by  the  very  remarkable  experi- 
ments of  Dr.  Edwards,  who  has  shown  that  cold-blooded  animals  live 
much  faster  (so  to  speak)  at  high  temperatures  than  at  low^ ;  so  that 
they  die  much  sooner  when  deprived  of  other  vital  stimuli.  Thus  when 
Frogs  w^ere  confined  in  a  limited  quantity  of  w^ater,  and  were  not  per- 
mitted to  come  to  the  surface  to  breathe,  it  w^as  found  that  the  dura- 
tion of  their  lives  was  inversely  proportioned  to  the  degree  ofheatof  the 
fluid.  Thus  when  it  was  cooled  dowm  to  the  freezing  point,  the  frogs 
immersed  in  it  lived  during  from  367  to  498  minutes.  At  the  tempe- 
rature of  50°,  the  duration  of  their  lives  w'as  from  350  to  375  minutes; 
at  72°,  it  was  from  90  to  35  minutes ;  at  90°,  from  12  to  32  minutes ; 
and  at  108°,  death  was  almost  instantaneous.  The  prolongation  of  life 
at  the  lower  temperatures  w^as  not  due  to  torpidity,  for  the  animals 
perform  the  functions  of  voluntary  motion,  and  enjoy  the  use  of  their 
senses;  but  it  is  occasioned  by  their  diminished  activity,  which  occa- 
sions a  less  demand  for  air.  On  the  other  hand,  the  elevation  of  tem- 
perature increases  the  demand  for  air,  and  causes  speedier  death  when 
it  is  withheld,  by  increasing  the  general  agility.  The  natural  habits  of 
these  animals  are  in  correspondence  with  these  facts.  Duringthe  winter, 
the  influence  of  a  sufficient  amount  of  aerated  water  upon  their  exte- 
rior serves  to  maintain  the  required  amount  of  respiration  through  the 
skin,  so  that  they  are  not  obliged  to  come  to  the  surface  to  take  in  air 
by  the  mouth.  As  the  season  advances,  however,  their  activity  in- 
creases, a  larger  amount  of  respiration  is  required,  and  the  animals  are 
obliged  to  come  frequently  to  the  surface  to  breathe.  During  summer 
the  yet  higher  temperature  calls  forth  an  increased  energy  and  activity 
in  all  the  vital  functions;  the  respiration  must  be  proportionably  in- 
creased ;  the  action  of  the  air  upon  the  cutaneous  surface,  as  well  as 
upon  the  lungs,  is  required ;  and  if  the  animals  are  prevented  from 
quitting  the  water  to  obtain  this,  they  die  as  soon  as  the  warmth  of 
the  season  becomes  considerable. 

134.  The  result  of  experiments  on  Fishes,  in  regard  to  the  depri- 
vation or  limited  supply  of  the  air  contained  in  the  water  in  which 
they  are  immersed,  is  exactly  similar ;  the  duration  of  life  being  in- 


OF  HEAT  AS  A  VITAL  STIMULUS.  95 

versely  as  the  temperature.  And  precisely  the  same  has  been  ascer- 
tained with  respect  to  hybernating  Mammals  ;  which,  as  already 
remarked,  are  for  a  time  reduced,  in  all  such  conditions,  to  the  level 
of  cold-blooded  animals. 

135.  Conformably  to  the  same  principle,  we  find  that  cold-blooded 
animals  are  enabled  to  sustain  the  deprivation  of  food  during  a  much 
longer  period,  at  cold  temperatures,  than  at  warm.  The  case  is  pre- 
cisely the  reverse  in  regard  to  most  warm-blooded  animals  ;  since  in 
them  a  due  supply  of  food  is  a  condition  absolutely  necessary  (as  we 
have  already  seen)  for  the  maintenance  of  that  amount  of  bodily  heat, 
whose  loss  is  fatal  to  them  ;  and  exposure  to  a  low  temperature  w^ill 
of  course  more  speedily  bring  about  that  crisis.  Hence  it  is  that  Cold 
and  Starvation  combined  are  so  destructive  to  life.  But  in  this  respect, 
also,  the  hybernating  Mammals  correspond  with  the  cold-blooded 
classes ;  their  power  of  abstinence  being  inversely  as  the  temperature 
of  their  bodies. 

136.  Although  a  very  low  temperature  is  positively  inconsistent 
with  the  continuance  of  vital  activity^  in  Animals  as  in  Plants,  yet 
we  find  that  even  very  severe  cold  is  not  necessarily  destructive  of 
the  vital  properties  of  organized  tissues  ;  so  that,  on  a  restoration  of 
the  proper  amount  of  heat,  their  functions  may  continue  as  before. 
Of  this  we  have  already  noticed  an  example,  in  the  case  of  frost-bitten 
limbs  ;  but  the  fact  is  much  more  remarkable,  when  considered  in 
reference  to  the  whole  body  of  an  animal,  and  the  complete  suspen- 
sion of  all  its  functions.  Yet  it  is  unquestionably  true,  not  only  of  the 
lowest  and  ^simplest  members  of  the  Animal  kingdom,  but  also  of 
Fishes  and  Reptiles.  In  one  of  Captain  Ross's  Arctic  Voyages, 
several  Caterpillars  of  the  Laria  Rossii  having  been  exposed  to  a 
temperature  of  40°  below  zero,  froze  so  completely,  that,  when  thrown 
into  a  tumbler,  they  chinked  like  lumps  of  ice.  When  thawed,  they 
resumed  their  movements,  took  food,  and  underwent  their  transform- 
ation into  the  Chrysalis  state.  One  of  them,  which  had  been  frozen 
and  thawed  four  times,  subsequently  became  a  Moth.  The  eggs  of  the 
Slug  have  been  exposed  to  a  similar  degree  of  cold,  without  the  loss 
of  their  fertility.  It  is  not  uncommon  to  meet,  in  the  ice  of  rivers, 
lakes,  and  seas,  with  Fishes  which  have  been  completely  frozen,  so 
as  to  become  quite  brittle  ;  and  which  yet  revive  when  thawed.  The 
same  thing  has  been  observed  in  regard  to  Frogs,  Newts,  &c.;  and 
the  experiment  of  freezing  and  subsequently  thawing  them,  has  been 
frequently  put  in  practice.  Spallanzani  kept  Frogs  and  Snakes  in  an 
ice-house  for  three  years  ;  at  the  end  of  which  period  they  revived  on 
being  subjected  to  warmth. 

137.  It  does  not  appear,  however,  that  the  same  capability  exists, 
in  regard  to  any  warm-blooded  animals ;  since  if  a  total  suspension* 
of  vital  activity  take  place  in  the  body  of  a  Bird  or  Mammal  for  any 

*  In  the  case  of  hybernating  Mammals,  the  suspension  is  not  total;  and  if  it  be 
rendered  such,  the  same  result  follows  as  in  other  instances. 


.$§  OF  HEAT  AS  A  VITAL  STIMULUS.      ^ 

length  of  time,  in  consequence  of  the  prolonged  application  of  severe 
cold,  recovery  is  found  to  be  impossible.  The  power  which  exists  in 
these  animals,  however,  of  generating  a  large  amount  of  heat  within 
their  bodies,  acts  as  a  compensation  for  the  want  of  the  faculty  pos- 
sessed by  the  cold-blooded  tribes  ;  since  they  can  resist  for  a  great 
length  of  time  (if  in  their  healthy  or  normal  condition)  the  depressing 
influence  of  a  temperature  sufficiently  low  to  produce  a  complete 
suspension  in  the  activity  of  the  latter. 

138.  It  only  remains  to  say  a  few  words  regarding  the  degree  of 
heat  w'hich  certain  Animals  can  sustain  without  prejudice,  and  which 
even  appears  to  be  genial  to  them.  Among  the  higher  classes,  this 
range  see?ns  to  be  capable  of  great  extension.  Thus  many  instances 
are  on  record  of  a  heat  of  from  250°  to  280°  being  endured,  in  dry 
air,  for  a  considerable  length  of  time,  without  much  inconvenience  ; 
and  persons  who  have  become  habituated  to  this  kind  of  exposure 
can  (with  proper  precautions)  sustain  a  temperature  of  from  350°  to 
500°.  In  all  such  cases,  however,  the  real  heat  of  the  body  under- 
goes very  little  elevation  ;  for,  by  means  of  the  copious  evaporation 
from  its  surface,  the  external  heat  is  prevented  from  acting  upon  it. 
But  if  this  evaporation  be  prevented,  either  by  an  insufficiency  in  the 
supply  of  fluid  from  within,  or  by  the  saturation  of  the  surrounding 
air  with  moisture,  the  temperature  of  the  body  begins  to  rise  ;  and  it 
is  then  found,  that  it  cannot  undergo  an  elevation  of  more  than  a  few 
degrees,  without  fatal  consequences.  Thus  in  several  experiments 
which  have  been  tried  on  different  species  of  warm-blooded  animals, 
for  the  purpose  of  ascertaining  the  highest  temperature  to  which  the 
body  could  be  raised  without  the  destruction  of  life,  it  was  found  that 
as  soon  as  the  heat  of  the  body  had  been  increased,  by  continued 
immersion  in  a  limited  quantity  of  hot  air  (which  would  soon  become 
charged  with  moisture),  to  from  9° — 13°  above  the  natural  standard, 
the  animals  died.  In  general.  Mammals  die,  when  the  temperature 
of  their  bodies  is  raised  to  about  111°;  the  heat  which  is  natural  to 
the  bodies  of  Birds.  The  latter  are  killed  by  an  equal  amount  of 
elevation  of  bodily  heat  above  their  natural  standard. 

139.  Hence  we  see  that  the  actual  range  of  temperature,  within 
which  vital  activity  can  be  maintained  in  warm-blooded  animals,  is 
extremely  limited  ;  a  temporary  elevation  of  the  bodily  heat  to  13° 
above  the  natural  standard,  or  a  depression  to  30°  below  it,  being 
positively  inconsistent,  not  merely  with  the  continuance  of  vital  ope- 
rations, but  also  with  the  preservation  of  vital  properties  ;  and  a  con- 
tinued departure  from  that  standard,  to  the  extent  of  only  a  very  few 
degrees  above  or  below  it,  being  very  injurious.  The  provisions 
■with  which  these  animals  are  endowed,  for  generating  heat  in  their 
interior,  so  as  to  supply  the  external  deficiency,  and  for  generating 
cold  (so  to  speak),  w^hen  the  external  temperature  is  too  high,  are 
therefore  in  no  respect  superfluous  :  but  are  positively  necessary  for 
the  maintenance  of  the  life  of  such  animals,  in  any  climate,  save  one 
whose  mean  should  be  conformable  to   their  standard,  and  w^hose 


OF  HEAT  AS  A  VITAL  STIMULUS.  97 

extremes  should  never  vary  more  than  a  very  few  degrees  above  or 
below  it.     Such  a  climate  does  not  exist  on  the  surface  of  the  earth. 

140.  The  range  oi  external  temperature,  within  which  cold-blooded 
animals  can  sustain  their  activity,  is  much  more  limited,  as  well  in* 
regard  to  its  highest  as  to  its  lowest  point ;  notwithstanding  that  the 
range  of  bodily  heat,  which  is  consistent  with  the  maintenance  of  their 
life,  is  so  much  greater.  In  those  which,  like  the  Frog,  have  a  soft 
moist  skin,  which  permits  a  copious  evaporation  from  the  surface,  a 
considerable  amount  of  heat  may  be  resisted,  provided  the  air  be  dry, 
and  the  supply  of  fluid  from  within  be  maintained.*  But  immersion 
in  w^ater  of  the  temperature  of  108°,  is  almost  immediately  fatal.  In 
many  other  cold-blooded  animals,  elevation  of  the  temperature  induces 
a  state  of  torpidity,  analogous  to  that  which  is  produced  by  its  de- 
pression. Thus  the  Helix  pomatia  (Edible  Snail)' has  been  found  to 
become  torpid  and  motionless  in  water  at  112°;  but  to  recover  its 
energy  when  placed  in  a  colder  situation.  It  would  seem  to  be  partly 
from  this  cause,  but  partly  also  from  the  deprivation  of  moisture,  that 
the  hottest  part  of  the  tropical  year  brings  about  a  cessation  of  activity 
in  many  tribes  of  cold-blooded  animals,  as  complete  as  that  which 
takes  place  during  the  winter  of  temperate  climates. 

141.  The  highest  limit  of  temperature  compatible  with  the  life  of 
Fishes  has  not  been  certainly  ascertained :  and  it  appears  probable 
that  there  are  considerable  variations  in  this  respect  amongst  different 
species.  Thus  it  is  certain  that  there  are  some  which  are  killed  by 
immersion  in  water  at  104°;  whilst  it  is  also  certain  that  others  can 
not  only  exist,  but  can  find  a  congenial  habitation,  in  water  of  113°, 
or  even  of  120°;  and  examples  of  the  existence  of  Fishes  in  thermal 
springs  of  a  much  higher  temperature  than  this,  have  been  put  on 
record.  Various  fresh  water  Mollusca  have  been  found  in  thermal 
springs,  the  heat  of  w^hich  is  from  100°  to  145°.  Rotifera  and  other 
animalcules  have  been  met  with  in  water  at  112°.  Larvae  of  Tipulee 
have  been  found  in  hot  springs  of  205°;  and  small  black  beetles, 
which  died  when  placed  in  cold  water,  in  the  hot  sulphur  baths  of 
Albano.  Entozoa  inhabiting  the  bodies  of  Mammalia  and  of  Birds 
must  of  course  be  adapted  to  a  constant  temperature  of  from  98°  to 
110°;  and  they  become  torpid  w^hen  exposed  to  a  cool  atmosphere. 
These  lowly  organized  animals  seem  more  capable  of  resisting  the 
effects  of  extreme  heat,  than  any  others; — at  least  if  we  are  to  credit 
the  statement,  that  the  Entozoa  inhabiting  the  intestines  of  the  Carp 
have  been  found  alive,  when  the  Fish  was  brought  to  table  after 
being  boiled. — In  all  such  cases,  it  is  to  be  remembered,  the  heat  of 
the  animal  body  must  correspond  with  that  of  the  fluid  in  which  it  is 

*  The  Frog  has  a  remarkable  provision  for  this  purpose  ;  in  a  bladder,  which  is 
strudurally  analogous  to  our  Urinary  bladder,  but  which  has  for  its  chief  function  to 
contain  a  store  of  fluids  for  the  exhaling  process.  It  has  been  noticed  that,  when  this 
store  is  exhausted  by  continued  exposure  of  the  animal  to  a  warm  dry  atmosphere,  the 
bladder  becomes  full  again,  when  the  animal  is  placed  in  a  moist  situation,  even  though 
it  take  in  no  liquid  by  its  mouth. 


9^  OF  ELECTRICITY  AS  A  VITAL  STIMULUS. 

immersed  ;  and  we  have  here,  therefore,  evident  proof  of  the  compati- 
bility of  vital  activity,  in  certain  cases,  with  a  very  elevated  tempera- 
ture. Additional  and  more  exact  observations,  however,  are  much 
wanting  on  this  subject. 

3.  On  Electricity y  as  a  Condition  of  Vital  Action. 

142.  Much  less  is  certainly  known  with  respect  to  the  ordinary 
influence  of  this  agent,  than  in  regard  to  either  of  the  two  preceding ; 
and  yet  there  can  be  little  doubt,  from  the  efiects  we  observe  when  it 
is  powerfully  applied,  as  well  as  from  our  knowledge  of  its  connection 
Avith  all  Chemical  phenomena,  that  it  is  in  constant  though  impercep- 
tible operation.  Electricity  differs  from  both  Light  and  Heat  in  this 
respect ; — that  no -manifestation  of  it  takes  place  so  long  as  it  is  uni- 
formly diffused,  or  is  in  a  state  of  equilibrium;  but  in  proportion  as 
this  equilibrium  is  disturbed,  by  a  change  in  the  electric  condition  of 
one  body,  which  is  prevented,  by  its  partial  or  complete  insulation, 
from  communicating  itself  to  others,  in  that  proportion  is  ^  force  pro- 
duced, which  exerts  itself  in  various  ways  according  to  its  degree. 
The  mechanical  effects  of  a  powerful  charge,  when  passed  through  a 
substance  that  is  a  bad  conductor  of  Electricity,  are  well  known  ;  on 
the  other  hand,  the  chemical  effects  of  even  the  feeblest  current  are 
equally  obvious.  The  agency  of  Electricity  in  producing  Chemical 
change  is  the  more  powerful,  in  proportion  as  there  is  already  a  pre- 
disposition to  that  change ;  thus,  as  already  remarked,  the  largest  col- 
lection of  oxygen  and  hydrogen  gases,  or  of  hydrogen  and  chlorine, 
mingled  together,  may  be  caused  to  unite  by  the  minutest  electric 
spark,  which  gives  the  required  stimulus  to  the  mutual  affinities  that 
were  previously  dormant.  Hence  it  cannot  but  be  inferred,  that  its 
agency  in  the  Chemical  phenomena  of  living  bodies  must  be  of  an 
important  character;  but  this  may  probably  be  exerted  rather  in  the 
way  of  aiding  decomposition,  than  of  producing  new  combinations, 
to  which  (as  we  have  seen)  Light  appears  to  be  the  most  effectual 
stimulus.  Thus  it  has  been  shown  that  pieces  of  meat,  that  have 
been  electrified  for  some  hours,  pass  much  more  rapidly  into  decom- 
position, than  similar  pieces  placed  under  the  same  circumstances, 
but  not  electrified.  And  in  like  manner,  the  bodies  of  animals  that 
have  been  killed  by  electric  shocks,  have  been  observed  to  putrify 
much  more  readily  than  those  of  similar  animals  killed  by  injury  to 
the  brain.  It  is  well  known,  moreover,  that  in  thundery  weather,  in 
which  the  electric  state  of  the  atmosphere  is  much  disturbed,  various 
fluids  containing  organic  compounds,  such  as  milk,  broth,  &c.,  are 
peculiarly  disposed  to  turn  sour  ;  and  that  saccharine  fluids,  such  as 
the  wort  of  brewers,  are  extremely  apt  to  pass  into  the  acetous  fer- 
mentation. 

143.  The  actual  amount  of  influence,  however,  which  Electricity 
exerts  over  a  growing  Plant  or  Animal,  can  scarcely  be  estimated. 
It  would,  perhaps,  be  the  most  correct  to  say,  that  the  state  of  Elec- 


i 


GF  ELECTRICITY  AS  A  VITAL  STIMULUS.  90 

trie  equilibrium  is  that  which  is  generally  most  favourable ;  and  we 
find  that  there  is  a  provision  in  the  structure  of  most  living  beings, 
for  maintaining  such  an  equilibrium, — not  only  between  the  different 
parts  of  their  own  bodies,  but  also  between  their  own  fabrics  and  the 
surrounding  medium.  Thus  a  charge  given  to  any  part  of  a  Plant  or 
Animal,  is  immediately  diffused  through  its  whole  mass;  and  though 
Organized  bodies  are  not  sufficiently  good  conductors  to  transmit  very 
powerful  shocks  without  being  themselves  affected,  yet  a  discharge 
of  any  moderate  quantity  may  be  effected  through  them,  without  any 
permanent  injury, — and  this  more  especially  if  it  be  made  to  take 
place  slowly.  Now  the  points  on  the  surfaces  of  Plants  appear  par- 
ticularly adapted  to  effect  this  transmission  ;  thus  it  has  been  found 
that  a  Leyden  jar  might  be  discharged  by  holding  a  blade  of  grass 
near  it,  in  one-third  of  the  time  required  to  produce  the  same  effect 
by  means  of  a  metallic  point ;  and  an  Electroscope  furnished  with 
Vegetable  points  has  been  found  to  give  more  delicate  indications  of 
the  electric  state  of  the  atmosphere,  than  any  other.  Plants  designed 
for  a  rapid  growth  have  generally  a  strong  pubescence  or  downy 
covering;  and  it  does  not  seem  improbable  that  one  purpose  of  this 
may  be,  to  maintain  that  equilibrium  between  themselves  and  the 
atmosphere,  which  would  otherwise  be  disturbed  by  the  various  ope- 
rations of  vegetation,  and  especially  by  the  process  of  evaporation, 
which  takes  place  with  such  activity  from  the  surface  of  the  leaves. 

144.  There  appears  to  be  sufficient  evidence  that,  during  a  highly 
electrical  state  of  the  atmosphere,  the  growth  of  the  young  shoots  of 
certain  plants  is  increased  in  rapidity ;  but  it  would  be  wrong  thence 
to  infer  that  this  excitement  is  useful  to  the  process  of  Vegetation  in 
general,  or  that  the  same  kind  of  electric  excitement  universally  ope- 
rates to  the  benefit  or  injury  of  the  Plant.  From  some  experiments 
recently  made  it  would  appear,  that  potatoes,  mustard  and  cress,  cine- 
rarias, fuchsias,  and  other  plants,  have  their  development,  and,  in 
some  instances,  their  productiveness,  increased  by  being  made  to 
grow  between  a  copper  and  a  zinc  plate,  connected  by  a  conducting 
wire  ;  while,  on  the  other  hand,  geraniums  and  balsams  are  destroyed 
by  the  same  influence.  The  transmission  of  a  series  of  moderate 
sparks  through  plants,  in  like  manner,  has  been  found  to  accelerate 
the  growth  of  some,  and  to  be  evidently  injurious  to  others.  It  is  not 
unreasonable  to  suppose,  that,  as  a  great  variety  of  chemical  processes 
are  constantly  taking  place  in  the  growing  plant,  an  electric  disturb- 
ance, which  acts  as  a  stimulus  to  some,  may  positively  retard  others; 
and  that  its  good  or  evil  results  may  thus  depend  upon  the  balance 
between  these  individual  effects.  This  would  seem  the  more  likely 
from  the  circumstance,  that,  in  the  process  of  Germination,  the  che- 
mical changes  concerned  in  which  are  of  a  simpler  character,  Elec- 
tricity seems  to  have  a  more  decided  and  uniform  influence.  The 
conversion  of  the  starch  of  the  seed  into  sugar,  which  is  an  essential 
part  of  this  change,  involves  the  liberation  of  a  large  quantity  of  car- 
bonic, and  of  some  acetic  acid.     Now  as  all  acids  are  negative,  and 


IGO  OF  ELECTRICITY  AS  A  VITAL  STIMULUS. 

as  like  electricities  repel  each  other,  it  may  be  inferred  that  the  seed 
is  at  that  time  in  an  electro-negative  condition  ;  and  it  is  accordingly 
found  that  the  process  of  germination  may  be  quickened,  by  connection 
of  the  seed  with  the  negative  pole  of  a  feeble  galvanic  apparatus, 
whilst  it  is  retarded  by  a  similar  connection  with  the  positive  pole. 
A  similar  acceleration  may  be  produced  by  the  contact  of  feeble  alka- 
line solutions,  which  favour  the  liberation  of  the  acids;  whilst,  on 
the  same  principle,  a  very  small  admixture  of  acid  in  the  fluid  with 
which  the  seed  is  moistened,  is  found  to  produce  a  decided  retarda- 
tion. 

145.  It  is  well  known  that  Trees  and  Plants  may  be  easily  killed 
by  powerful  electric  shocks;  and  that,  when  the  charge  is  strong 
enough  (as  in  the  case  of  a  stroke  of  lightning),  violent  mechanical 
effects, — as  the  rending  of  trunks,  or  even  the  splitting  and  scattering 
of  minute  fragments, — are  produced  by  it.  But  it  has  also  been 
ascertained,  that  charges  which  produce  no  perceptible  influence  of 
this  kind,  may  destroy  the  life  of  Plants;  though  the  effect  is  not 
always  immediate.  In  particular  it  has  been  noticed,  that  slips  and 
grafts  are  prevented  from  taking  root  and  budding.  There  can  be 
little  doubt  that,  in  these  instances,  a  change  is  effected  in  the  chemi- 
cal state  of  the  solids  or  fluids ;  although  no  structural  alteration  is 
perceptible. 

146.  In  regard  to  the  influence  of  Electricity  upon  the  Organic 
functions  of  Animals,  still  less  is  certainly  known  ;  but  there  is  evi- 
dence that  it  may  act  as  a  powerful  stimulant  in  certain  disordered 
states  of  them.  Thus  in  Amenorrhea,  a  series  of  slight  but  rapidly- 
repeated  electric  shocks  will  often  bring  on  the  catamenial  flow ;  and 
it  is  certain  that  chronic  tumours  have  been  dispersed,  and  dropsies 
relieved  by  the  excitement  of  the  absorbent  process,  through  similar 
agency.  Again,  it  is  indubitable  that  a  highly  electric  state  of  the 
atmosphere  produces  very  marked  effects  on  the  general  state  of  many 
individuals ;  and  brings  on  in  some  a  degree  of  languor  and  depres- 
sion, which  cannot  be  accounted  for  in  any  other  way.  An  instance 
is  on  record,  in  which  the  atmosphere  w^as  in  such  an  extraordinary 
state  of  electric  disturbance,  that  all  pointed  bodies  within  its  influ- 
ence exhibited  a  distinct  luminosity  ;  and  it  was  noticed,  that  all  the 
persons  who  were  exposed  to  the  agency  of  this  highly  electrified  air, 
experienced  spasms  in  the  limbs  and  an  extreme  state  of  lassitude, 

147.  Animals,  like  Plants,  are  liable  to  be  killed  by  shocks  of  Elec- 
tricity; even  when  these  are  not  sufficiently  powerful  to  occasion  any 
obvious  physical  change  in  their  structure.  But,  as  formerly  men- 
tioned (§  69)  there  can  be  no  doubt  that  minute  changes  may  be 
produced  in  their  delicate  parts,  which  are  quite  sufficient  to  account 
for  the  destruction  of  their  vitality,  ev^en  though  these  can  only  be 
discerned  with  the  Microscope.  The  production  of  changes  in  the 
Chemical  arrangement  of  their  elements,  is,  however,  a  much  more 
palpable  cause  of  death ;  since  it  maybe  fully  anticipated  beforehand, 
and  can  easily  be  rendered  evident.     To  take  one  instance  only ; — 


OF  MOISTURE  AS  A  VITAL  STIMULUS,  IQl 

it  is  well  known,  that  albumen  is  made  to  coagulate,  i.  e.,  is  changed 
from  its  soluble  to  its  insoluble  form,  under  the  influence  of  an  elec- 
tric current;  and  it  cannot  be  doubted  that  the  production  of  this 
change  in  the  fluids  of  the  living  body  (almost  every  one  of  which  con- 
tains albumen),  even  to  a  very  limited  extent,  is  quite  a  sufficient 
cause  of  death,  even  in  animals  that  are  otherwise  most  tenacious  of 
life.  "  I  once  discharged  a  battery  of  considerable  size,"  says  Dr. 
Hodgkin,  "  through  a  common  Earth-worm,  which  would  in  all  pro- 
bability have  shown  signs  of  life  long  after  minute  division.  Its 
death  was  as  sudden  as  the  shock;  and  the  semi-transparent  sub- 
stance of  the  animal  was  changed  like  Albumen  which  has  been 
exposed  to  heat.^' 

148.  Electricity  possesses,  in  a  remarkable  degree,  the  power  of 
exciting  the  Contractility  of  Muscular  fibre  ;  but  this  series  of  pheno- 
mena will  be  more  fitly  described,  when  the  properties  of  that  tissue 
are  under  consideration. 

4.   Of  Moisture,  as  a  Condition  of  Vital  Action. 

149.  Independently  of  the  utility  of  Water  as  an  article  of  food, 
and  of  the  part  it  performs  in  the  Chemical  operations  of  the  living 
body,  by  supplying  two  of  their  most  important  materials  (oxygen  and 
hydrogen),  there  can  be  no  doubt  that  a  certain  supply  of  moisture  is 
requisite,  as  one  of  the  conditions  without  which  no  vital  actions  can 
go  on.  It  has  been  already  remarked,  indeed,  that  one  of  the  distin- 
guishing peculiarities  of  organized  structures,  is  the  presence  in  all 
of  them  of  solid  and  fluid  component  parts ;  and  this  in  the  minutest 
portions  of  the  organism,  as  well  as  in  the  aggregate  mass.  And  in 
all  the  vital,  as  well  as  in  the  chemical  actions,  to  which  these  struc- 
tures are  subservient,  the  presence  of  fluid  is  essential.  All  nutrient 
materials  must  be  reduced  to  the  fluid  form,  before  they  can  be  assimi- 
lated by  the  solids  ;  and,  again,  the  solid  matters  which  are  destined 
to  be  carried  ofi'  by  excretion,  must  be  again  reduced  to  the  liquid 
state,  before  they  can  be  thus  withdrawn  from  the  body.  The  tissues 
in  which  the  most  active  changes  of  a  purely  vital  character  are  per- 
formed,— namely,  the  Nervous  and  Muscular, — naturally  contain  a 
very  large  proportion  of  water;  the  former  as  much  as  80,  and  the 
latter  77,  per  cent.  On. the  other  hand,  in  tissues  whose  function  is 
of  a  purely  mechanical  nature,  such  as  Bone,  the  amount  of  fluid  is 
as  small  as  is  consistent  with  the  maintenance  of  a  certain  amount  of 
nutrient  action  in  its  interior.  By  the  long-continued  application  of 
dry  heat  to  a  dead  body,  its  weight  was  found  to  be  reduced  from 
120  pounds  to  no  more  than  12  ;  so  that,  taking  the  average  of  the 
whole,  the  amount  of  water,  not  chemically  combined,  but  simply 
interstitial,  might  be  reckoned  at  as  much  as  90  per  cent.  It  is  cer- 
tain, however,  that  much  decomposition  and  loss  of  solid  matter  must 
have  taken  place  in  this  procedure  ;  and  we  shall  probably  estimate 
the  proportion  more  accurately,  if  we  regard  the  weight  of  the  fluids 


102  OF  MOISTURE  AS  A  VITAL  STIMULUS. 

of  the  human  body  as  exceeding  that  of  the  solids  by  six  or  seven 
times. 

150.  There  is  a  great  variation  in  this  respect,  however,  among 
different  tribes  of  living  beings.  There  are  probably  no  highly- 
organized  Animals,  v^^hose  texture  contains  less  fluid  than  that  of  Ver- 
tebrata  (unless,  it  may  be,  certain  Beetles);  but  there  can  be  no  ques- 
tion that,  among  some  of  the  Zoophytes,  the  proportion  of  solids  to 
fluids  is  just  the  other  way.  In  those  massive  coral-forming  animals, 
which,  seem  to  have  been  expressly  created  for  the  purpose  of  build- 
ing up  islands  and  even  continents  from  the  depths  of  the  ocean,  we 
find  the  soft  tissues  confined  to  the  surface,  and  all  within  of  a  rocky 
hardness.  It  is  not,  however,  correct  to  say  (as  is  commonly  done), 
that  the  coral-polypes  build  up  these  stony  structures  as  habitations 
for  themselves;  for  the  stony  matter  is  deposited,  by  an  act  of  nutri- 
tion, in  the  living  tissue  of  these  animals,  just  as  much  as  it  is  in  the 
bones  of  Man.  But  the  parts  once  consolidated  henceforth  remain 
dead,  so  far  as  the  animal  is  concerned  ;  they  are  not  connected  with 
the  living  tissues  by  any  vessels,  nerves,  &c.;  their  density  prevents 
them  from  undergoing  any  but  a  very  slow  disintegrating  change,  so 
that  they  require  and  receive  no  nutrient  materials ;  and  they  might 
be  altogether  removed,  by  accident  or  decay,  without  any  direct  in- 
jury to  the  still  active,  because  yet  unconsolidated,  portions  of  the 
polype-structure. 

151.  There  is  a  close  correspondence,  in  this  respect,  between  the 
condition  of  the  stony  or  horny  stem  of  a  Coral,  and  the  heart-wood  of 
the  trunk  of  a  Tree ;  for  the  latter,  becoming  consolidated  by  internal 
deposit,  for  the  purpose  of  affording  mechanical  support,  is  thence- 
forth totally  unconnected  with  the  vegetative  operations  of  the  tree, 
and  might  be  removed  (as  it  frequently  is  by  natural  decay)  without 
affecting  them.  In  all  the  parts,  in  which  the  nutrient  processes  are 
actively  going  on,  do  we  observe  that  the  tissue  contains  a  large  pro- 
portion of  water ;  and  that,  if  the  succulent  portions  be  dried  up, 
their  vital  properties  are  destroyed.  Thus  it  is  in  the  soft  tissue  at 
the  extremities  of  the  radicles  or  root  fibres,  that  the  function  of 
absorption  takes  place  with  the  greatest  activity;  so  that  these  parts 
have  received  the  name  of  spongioles:  it  is  in  the  cells  which  form 
the  soft  parenchyma  of  the  leaves,  that  the  elaboration  of  the  sap 
takes  place,  the  fixation  of  carbon  from  the  atmosphere,  and  the  pre- 
paration of  the  peculiar  secretions  of  the  plant:  and  it  is  in  the  space 
between  the  bark  and  the  wood,  which  is  occupied  (at  the  season  of 
most  active  growth)  by  a  saccharine  glutinous  fluid,  that  the  formation 
of  the  new  layers  of  wood  and  bark  takes  place.  Now,  as  soon  as 
these  parts  become  consolidated,  they  cease  to  perform  any  active 
vital  operations.  The  spongioles,  by  the  lengthening  of  the  root- 
fibres,  become  converted  into  a  portion  of  those  fibres,  and  remain 
subservient  merely  to  the  transmission  of  the  fluids  absorbed  ;  the 
leaves  gradually  become  choked  by  the  saline  and  earthy  particles 
contained  in  the  ascending  sap,  which  they  have  had  no  power  of 


OF  MOISTURE  AS  A  VITAL  STIMULUS.  103 

excreting,  and  they  wither,  die,  and  fall  off;  and  the  new  layers  of 
wood  and  bark,  when  once  formed,  undergo  but  little  further  change, 
and  are  subservient  to  little  else  than  the  transmission  of  the  ascend- 
ing and  descending  sap  to  the  parts  where  they  are  to  be  respectively 
appropriated. 

152.  There  are  some  remarkable  instances  in  both  the  Animal  and 
Vegetable  kingdoms,  of  an  immense  preponderance  in  the  amount  of 
the  fluids  over  that  of  the  solids  of  the  structure.  This  is  character- 
istic of  the  whole  class  of  Jicalephce  or  Jelly-Fish^  giving  to  their 
tissues  that  softness  from  which  their  common  name  is  derived  ;  these 
animals,  in  consequence,  are  unable  to  live  out  of  water;  for,  when 
they  are  removed  from  it,  a  drain  of  their  fluids  commences,  which 
soon  reduces  their  weight  to  a  degree  that  destroys  their  lives, — a 
Medusa  weighing  fifty  pounds  being  thus  dried  down  to  a  weight  of 
as  many  grains.  The  most  remarkable  instances  of  a  parallel  kind 
among  Plants,  are  to  be  found  in  the  tribe  of  Fungi ;  certain  mem- 
bers of  which  are  distinguished  by  an  almost  equally  small  proportion 
of  solid  materials  in  their  textures,  presenting  a  most  delicate  gossa- 
mer-like appearance  to  the  eye,  and  possessing  such  little  durability, 
that  they  come  to  maturity  and  undergo  decay  in  the  course  of  a  few 
hours.  These  are  not  inhabitants  of  the  water,  but  will  vegetate  only 
in  a  very  damp  atmosphere. 

153.  As  we  find  various  Plants  and  Animals  very  differently  con- 
structed in  regard  to  the  amount  of  fluid  contained  in  their  tissues,  so 
do  we  also  find  them  dependent  in  very  different  degrees  upon  a  con- 
stant supply  of  external  moisture.  There  is  no  relation,  however, 
between  the  succulence  of  a  plant,  and  the  degree  of  its  dependence 
upon  water;  in  fact,  we  commonly  find  the  most  succulent  plants 
growing  in  the  driest  situations;  whilst  the  plants,  which  are  adapted 
to  localities  where  they  can  obtain  a  constant  supply  of  fluid,  are  not 
usually  remarkable  for  the  amount  of  water  in  their  own  structure. 
This,  however,  is  easily  explained.  We  find  the  most  succulent 
plants, — such  as  the  Sedums  or  Stone-crops  of  our  own  country,  and 
the  Cacti  and  Euphorbice  of  the  tropics, — in  dry  exposed  situations, 
where  they  seem  as  if  they  would  be  utterly  destitute  of  nutriment. 
The  fact  is,  however,  that  they  lose  their  fluid  by  exhalation  very 
slowly,  in  consequence  of  their  small  number  of  stomata ;  whilst,  on 
the  other  hand,  they  absorb  with  great  readiness  during  rainy  weather, 
and  are  enabled,  by  the  fleshiness  of  their  substance,  to  store  up  a 
large  quantity  of  moisture  until  it  is  required.  In  some  parts  of 
Mexico,  the  heat  is  so  intense,  and  the  soil  and  atmosphere  so  dry, 
during  a  large  part  of  the  year,  that  no  vegetation  is  found  at  certain 
seasons,  save  a  species  of  Cactus  ;  this  affords  a  wholesome  and 
refreshing  article  of  food,  on  which  travelers  have  been  able  to 
subsist  for  many  days  together,  and  without  which  these  tracts  would 
form  impassable  barriers.  On  the  other  hand,  the  plants  of  damp 
situations  usually  exhale  moisture  almost  as  fast  as  they  imbibe  it ; 
and  consequently,  if  their  usual  supply  be  cut  off  or  diminished,  they 


104  OF  MOISTURE  AS  A  VITAL  STIMULUS. 

soon  wither  and  die.  Plants  that  usually  live  entirely  submerged, 
are  destitute  of  the  cuticle  or  thin  skin,  which  covers  the  surface  in 
other  cases  ;  in  consequence  of  this,  they  very  rapidly  lose  their  fluid, 
when  they  are  removed  from  the  water  ;  and  they  are  hence  depend- 
ent upon  constant  immersion  in  it  for  the  continuance  of  their  lives, 
although  their  tissues  may  not  be  remarkable  for  the  amount  of  fluid 
which  they  contain. 

154.  There  are  some  Plants  which  are  capable  of  adapting  them- 
selves to  a  great  variety  of  situations,  differing  widely  as  to  the 
amount  of  moisture  which  their  inhabitants  can  derive  from  the  soil 
and  atmosphere  ;  and  we  may  generally  notice  a  marked  difference 
in  the  mode  of  growth,  when  we  compare  individuals  that  have 
grown  under  opposite  circumstances.  Thus  a  plant  from  a  dry 
exposed  situation,  shall  be  stunted  and  hairy,  whilst  another,  of  the 
same  species,  but  developed  in  a  damp  sheltered  situation,  shall  be 
rank  and  glabrous  (smooth).  But  in  general  there  is  a  certain  quan- 
tity of  moisture  congenial  to  each  species ;  and  the  excess  or  deficiency 
of  this  condition  has,  in  consequence,  as  great  an  influence  in  deter- 
mining the  geographical  distribution  of  Plants,  as  the  amount  of  light 
and  heat.  Thus,  as  already  remarked,  the  Orchidese  and  Tree  Ferns 
of  the  tropics  grow  best  in  an  atmosphere  loaded  with  dampness ; 
whilst  the  Cactus  tribe,  for  the  most  part,  flourishes  best  in  dry 
situations.  The  former  become  stunted  and  inactive,  if  limited  in 
their  supply  of  aerial  moisture  ;  whilst  the  latter,  if  too  copiously 
nourished,  become  dropsical  and  liable  to  rot.  Among  the  plants  of 
our  own  country,  we  find  a  similar  limitation ;  a  moist  boggy  situation 
being  indispensable  to  the  growth  of  some,  whilst  a  dry  exposed 
elevation  is  equally  essential  to  the  healthy  development  of  others. 
There  is  a  beautiful  species  of  exotic  Fern,  the  Trichomanes  sped- 
osum ;  the  rearing  of  which  has  been  frequently  attempted  in  this 
country  and  elsewhere,  without  success  ;  but  which  only  requires  an 
atmosphere  saturated  with  dampness,  for  its  healthy  development, 
being  easily  reared  in  one  of  Mr.  Ward's  closed  glass  cases.  In  this, 
as  in  similar  examples,  it  is  only  necessary  to  imitate  as  closely  as 
possible  the  conditions  under  which  the  species  naturally  grows  ;  and 
sometimes  this  can  only  be  accomplished,  by  surrounding  the  plant  with 
small  trees  and  shrubs,  so  as  to  give  it  a  moister  atmosphere  than  it 
could  otherwise  attain.  Professor  Royle  mentions  the  growth,  under 
such  circumstances,  of  a  fine  specimen  of  the  Xanthochymus  dulcis, 
one  of  the  Guttiferce  or  Gamboge-trees,  in  the  garden  of  the  King  of 
Delhi ;  this  tree  is  naturally  found  only  in  the  southern  parts  of  India; 
and  the  success  of  its  cultivation  in  this  northerly  situation  is  entirely 
due  to  its  being  sheltered  by  the  numerous  buildings  within  the  lofty 
palace  wall,  surrounded  by  almost  a  forest  of  trees,  and  receiving  the 
benefit  of  perpetual  irrigation  from  a  branch  of  the  canal  which  flows 
through  the  garden. 

155.  In  regard  to  the  influence  of  external  moisture  upon  Animal 
life,  there  is  much  less  to  be  said ;  since  the  mode  in  which  fluid  is 


OF  MOISTURE  AS  A  VITAL  STIMULUS.  105 

received  into  the  system  is  so  entirely  different.  It  may  be  remark- 
ed, however,  that  Animals  habitually  living  beneath  the  water,  like 
submerged  Plants,  are  usually  incapable  of  sustaining  life  for  any 
length  of  time  when  removed  from  it,  in  consequence  of  the  rapid 
loss  of  fluid  which  they  undergo  from  their  surface.  It  is,  however, 
by  the  desiccation  of  the  respiratory  surface,  preventing  the  due  aera- 
tion of  the  blood,  that  the  fatal  result  is  for  the  most  part  occasioned; 
since  we  find  that  when  there  is  a  special  provision  to  prevent  this, 
as  in  the  case  of  certain  Fishes  and  Crustacea,  the  animals  can  quit 
the  water  for  a  great  length  of  time.  There  can  be  no  doubt  that  the 
amount  of  Atmospheric  moisture  is  one  of  those  conditions,  which 
are  collectively  termed  Climate,  and  which  influence  the  geographical 
distribution  of  Animals,  no  less  Ihan  that  of  Plants.  But  it  is  difficult 
to  say  how  far  the  variations  in  moisture  act  alone.  There  can  be 
no  doubt,  however,  of  their  operation  ;  for  every  one  is  conscious 
of  the  effect,  upon  his  health  and  spirits,  of  such  variations  as  take 
place  in  the  climate  he  may  inhabit.  The  two  principal  modes  in 
which  these  will  operate,  will  be  by  accelerating  or  checking  the 
exhalation  of  fluid  from  the  skin  and  from  the  pulmonary  surface  ; 
for  when  the  air  is  already  loaded  with  dampness,  the  exhaled  mois- 
ture cannot  be  carried  off  with  the  same  readiness  as  w^hen  it  is  in  a 
condition  of  greater  dryness  ;  and  it  will  consequently  either  remain 
within  the  system,  or  it  will  accumulate  and  form  sensible  perspira- 
tion. 

156.  Now  each  of  these  states  may  be  salutary,  being  the  one  best 
adapted  to  particular  constitutions,  or  to  different  states  of  the  same 
individual.  A  cold  drying  wind  shall  be  felt  as  invigorating  to  the 
relaxed  frame,  as  it  is  chilling  to  one  that  has  no  warmth  or  moisture 
to  spare  ;  on  the  other  hand,  a  warm  damp  atmosphere,  which  is 
refreshing  to  the  latter,  shall  be  most  depressing  to  the  former.  All 
who  have  tried  the  effect  of  closely-fitting  garments,  impervious  to 
moisture,  are  well  aware  how  oppressive  they  soon  become  ;  this  feel- 
ing being  dependent  upon  the  obstruction  they  occasion  to  the  act 
of  perspiration,  by  causing  the  included  air  to  be  speedily  saturated 
with  moisture.  When  the  fluids  of  the  system  have  been  diminished 
in  amount,  either  by  the  suspension  of  a  due  supply  of  water,  or  by 
an  increase  in  the  excretions,  there  is  a  peculiar  refreshment  in  a 
soft  damp  atmosphere,  or  in  a  warm  bath,  w^hich  allows  the  loss  to 
be  replaced  by  absorption  through  the  general  cutaneous  surface. 
The  reality  of  such  absorption  has  been  placed  beyond  all  doubt, 
by  observations  upon  men,  who  had  been  exposed  to  a  hot  dry  air 
for  some  time,  and  afterwards  placed  in  a  warm  bath  ;  for  it  was 
found  that  the  system  would  by  this  unusual  means  supply  the 
deficiency,  which  had  been  created  by  the  previous  increase  in  the 
transpiration. 

157.  The  effect  of  a  moist  or  dry  atmosphere,  then,  upon  the  Ani- 
mal body,  cannot  be  by  any  means  unimportant  ;  although,  as  we 
shall  hereafter  see,  there  exists  in  it  a  series  of  the  most  remarkable 


106  OF  MOISTURE  AS  A  VITAL  STIMULUS. 

provisions  for  regulating  the  amount  of  its  fluids.  The  influence  of 
atmospheric  moisture,  however,  is  most  obvious  in  disordered  states 
of  the  system.  Thus  in  persons  who  are  subject  to  the  form  of 
Dyspepsia  called  atonic,  which  is  usually  connected  with  a  gene- 
rally-relaxed condition  of  the  system,  a  very  perceptible  influence  is 
experienced  from  changes  in  the  quantity  of  atmospheric  moisture  ; 
the  digestive  power,  as  well  as  the  general  functions  of  the  body, 
being  invigorated  by  dryness,  and  depressed  by  damp.  Again,  there 
is  no  doubt  that,  where  a  predisposition  exists  to  the  Tuberculous 
Cachexia,  it  is  greatly  favoured  by  habitual  exposure  to  a  damp 
atmosphere,  especially  when  accompanied  by  cold  ;  indeed  it  would 
appear,  from  the  influence  of  cold  damp  situations  upon  animals 
brought  from  warmer  climates,  that  these  two  causes  may  induce  the 
disease,  in  individuals  previously  healthy.  On  the  other  hand,  there 
are  some  forms  of  pulmonary  complaints,  in  which  an  irritable  state 
of  the  mucous  membrane  of  the  bronchial  tubes  has  a  large  share  ; 
when  this  irritation  presents  itself  in  the  dry  form,  a  warm  moist 
atmosphere  is  found  most  soothing  to  it;  whilst  a  drier  and  more 
bracing  air  is  much  more  beneficial,  when  the  irritation  is  accom- 
panied by  a  too  copious  secretion. 

158.  Although,  as  already  stated,  no  vital  actions  can  go  on  with- 
out a  reaction  between  the  solids  ^nd  fluids  of  the  body,  yet  there  may 
be  an  entire  loss  of  the  latter,  in  certain  cases,  without  necessarily 
destroying  life;  the  structure  being  reduced  to  a  state  of  dormant 
vitality,  in  w^hich  it  may  remain  unchanged  for  an  unlimited  period  ; 
and  yet  being  capable  of  renewing  all  its  actions,  when  moisture  is 
again  supplied.  Of  this  we  find  numerous  examples  among  both  the 
Vegetable  and  the  Animal  kingdoms.  Thus  the  Mosses  and  Liver- 
worts, which  inhabit  situations  where  they  are  liable  to  occasional 
drought,  do  not  suffer  from  being,  to  all  appearance,  completely  dried 
up;  but  revive  and  vegetate  actively,  as  soon  as  they  have  been 
thoroughly  moistened.  Instances  are  recorded,  in  which  Mosses  that 
have  been  for  many  years  dried  up  in  a  Herbarium,  have  been  re- 
stored by  moisture  to  active  life.  There  is  a  lycopodium  (Club-Moss) 
inhabiting  Peru,  which,  when  dried  up  for  want  of  moisture,  folds  its 
leaves  and  contracts  into  a  ball ;  and  in  this  state,  apparently  quite 
devoid  of  animation,  it  is  blown  hither  and  thither  along  the  surface 
by  the  wind.  As  soon,  however,  as  it  reaches  a  moist  situation,  it 
sends  down  its  roots  into  the  soil,  and  unfolds  to  the  atmosphere  its 
leaves,  which,  from  a  dingy  brown,  speedily  change  to  the  bright 
green  of  active  vegetation.  The  Anastatica  (Rose  of  Jericho)  is  the 
subject  of  similar  transformations;  contracting  into  a  ball,  when  dried 
up  by  the  burning  sun  and  parching  air ;  being  detached  by  the  wind 
from  the  spot  where  its  slender  roots  had  fixed  it,  and  rolled  over  the 
plains  to  indefinite  distances;  and  then,  when  exposed  to  moisture, 
unfolding  its  leaves,  and  opening  its  rose-like  flower,  as  if  roused 
from  sleep.  There  is  a  blue  Water- Lily,  abounding  in  several  of  the 
canals  at  Alexandria,  which  at  certain  seasons  become  so  dry,  that 


OF  MOISTURE  AS  A  VITAL  STIMULUS.  107 

their  beds  are  burnt  as  hard  as  bricks  by  the  action  of  the  sun,  so  as 
to  be  fit  for  use  as  carriage  roads ;  yet  the  plants  do  not  thereby  lose 
their  vitality ;  for  when  the  water  is  again  admitted,  they  resume  their 
growth  with  redoubled  vigour. 

159.  Among  the  lower  Animals,  we  find  several  of  considerable 
complexity  of  structure,  which  are  able  to  sustain  the  most  complete 
desiccation.  This  is  most  remarkably  the  case  in  the  common  Wheel- 
Animalcule;  which  may  be  reduced  to  a  state  of  most  complete  dry- 
ness, and  kept  in  this  condition  for  any  length  of  time,  and  which  will 
yet  revive  immediately  on  being  moistened.  The  same  individuals 
may  be  treated  in  this  manner,  over  and  over  again.  Experiments 
have  been  carried  still  further  with  the  allied  tribe  of  Tardigrades ; 
individuals  of  which  have  been  kept  in  a  vacuum  for  thirty  days, 
with  sulphuric  acid  and  Chloride  of  Calcium  (thus  suffering  the  most 
complete  desiccation  the  Chemist  can  effect),  and  yet  have  not  lost 
their  vitality.  It  is  singular  that  in  this  desiccated  condition,  they 
may  be  heated  to  a  temperature  of  250°,  without  the  destruction  of 
their  vitality;  although,  when  in  full  activity,  they  will  not  sustain  a 
temperature  of  more  than  from  112°  to  115°.  Some  of  the  minute 
Entomostracous  Crustacea,  which  are  nearly  allied  to  the  Rotifera, 
appear  to  partake  with  them  in  this  curious  faculty.  Many  instances 
are  on  record,  in  which  Snails  and  other  terrestrial  Molhisca  have 
revived,  after  what  appeared  to  be  complete  desiccation  ;  and  the 
eggs  of  the  Slug,  when  dried  up  by  the  sun  or  by  artificial  heat,  and 
reduced  to  minute  points  only  visible  with  the  Microscope,  are  found 
not  to  have  lost  their  fertility,  when  they  are  moistened  by  a  shower 
of  rain,  or  by  immersion  in  water,  which  restores  them  to  their  former 
plumpness.  Even  after  being  treated  eight  times  in  this  manner,  the 
eggs  were  hatched  when  placed  in  favourable  circumstances ;  and 
even  eggs  in  which  the  embryo  was  distinctly  formed,  survived  such 
treatment  without  damage.  That  such  capability  should  exist  in  the 
animals  and  eggs  just  mentioned,  shows  a  remarkable  adaptation  to 
the  circumstances  in  which  they  are  destined  to  exist ;  since  were  it 
not  for  their  power  of  surviving  desiccation,  the  races  of  Wheel- 
Animalcules  and  Entomostraca  must  speedily  become  extinct,  through 
the  periodical  drying-up  of  the  small  collections  of  water  which  they 
inhabit ;  and  a  season  of  prolonged  drought  must  be  equally  fatal  to 
the  terrestrial  MoUusca. 

160.  It  would  seem  that  many  cold-blooded  animals  are  reduced, 
by  a  moderate  deficiency  of  fluid,  to  a  state  of  torpidity  closely  resem- 
bling that  induced  by  cold ;  and  hence  it  is,  that  during  the  hottest 
and  driest  part  of  the  tropical  year,  there  is  almost  as  complete  an 
inactivity,  as  in  the  winter  of  temperate  regions.  The  common  Snail, 
if  put  into  a  box  without  food,  constructs  a  thin  operculum  or  parti- 
tion across  the  orifice  of  the  shell,  and  attaches  itself  to  the  side  of 
the  box:  in  this  state  it  may  remain  dormant  for  years,  without  being 
affected  by  any  ordinary  changes  of  temperature ;  but  it  will  speedily 
revive  if  plunged  in  water.     Even  in  their  natural  haunts,  the  ter- 


108  OF  MOISTURE  AS  A  VITAL  STIMULUS. 

restrial  Mollusca  of  our  own  climates  are  often  found  in  this  state 
during  the  summer,  when  there  is  a  continued  drought;  but  with  the 
first  shower  they  revive  and  move  about.  In  like  manner  it  is  ob- 
served that  the  rainy  season,  between  the  tropics,  brings  forth  the 
hosts  of  insects,  which  the  drought  had  caused  to  remain  inactive  in 
their  hiding-places.  Animals  thus  rendered  torpid  seem  to  have  a 
tendency  to  bury  themselves  in  the  ground,  like  those  which  are 
driven  to  winter-quarters  by  cold.  Mr.  Darwin  mentions  that  he 
observed,  with  some  surprise,  at  Rio  de  Janeiro,  that,  a  few  days 
after  some  little  depressions  had  been  changed  into  pools  of  water 
by  the  rain,  they  were  peopled  by  numerous  full-grown  shells  and 
beetles. 

161.  This  torpidity  consequent  upon  drought  is  not  confined  to 
Invertebrated  animals.  There  are  several  Fish,  inhabiting  fresh 
water,  which  bury  themselves  in  the  mud  when  their  streams  or  pools 
are  dried  up,  and  which  remain  there  in  a  torpid  condition  until  they 
are  again  moistened.  This  is  the  case  with  the  curious  Lepidosiren, 
which  forms  so  remarkable  a  connecting  link  between  Fishes  and  the 
Batrachian  Reptiles;  it  is  an  inhabitant  of  the  upper  parts  of  the 
river  Gambia,  which  are  liable  to  be  dried  up  during  much  more  than 
half  the  year;  and  the  whole  of  this  period  is  spent  by  it  in  a  hollow 
which  it  excavates  for  itself  deep  in  the  mud,  where  it  lies  coiled  up 
in  a  completely  torpid  condition, — whence  it  is  called  by  the  natives 
the  sleeping-fish.  When  the  return  of  the  rainy  season  causes  the 
streams  to  be  again  filled,  so  that  the  water  finds  its  way  down  to  the 
hiding-place  of  the  Lepidosiren,  it  comes  forth  again  for  its  brief 
period  of  activity;  and  with  the  approach  of  drought,  it  again  works 
its  way  down  into  the  mud,  which  speedily  hardens  around  it  into  a 
solid  mass.  In  the  same  manner,  the  Pi^oteus^  an  inhabitant  of  certain 
lakes  in  the  Tyrol,  which  are  liable  to  be  periodically  dried  up,  retires 
at  these  periods  to  the  underground  passages  that  connect  them,  where 
it  is  believed  to  remain  in  a  torpid  condition;  and  it  thence  emerges 
into  the  lakes,  as  soon  as  they  again  become  filled  with  water.  The 
Lizards  and  Serpents,  too,  of  tropical  climates,  appear  to  be  subject  to 
the  same  kind  of  torpidity,  in  consequence  of  drought,  as  that  which 
affects  those  of  temperate  regions  during  the  cold  of  winter.  Thus 
Humboldt  has  related  the  strange  accident  of  a  hovel  having  been 
built  over  a  spot,  where  a  young  Crocodile  lay  buried,  alive  though 
torpid,  in  the  hardened  mud;  and  he  mentions  that  the  Indians  often 
find  enormous  Boas  in  the  same  lethargic  state  ;  and  that  these  revive 
when  irritated  or  wetted  with  water. — All  these  examples  show  the 
necessity  of  a  fixed  amount  of  fluid,  in  the  animal  structure,  for  the 
maintenance  of  vital  activity ;  whilst  they  also  demonstrate,  that  rtie 
preservation  of  the  v\\?i\  properties  of  that  structure  is  not  always  in- 
compatible with  the  partial,  or  even  the  complete,  abstraction  of  that 
fluid;  the  solid  portions  being  then  much  less  liable  to  decomposition 
by  heat,  or  by  other  agencies,  than  they  are  in  their  ordinary  con- 
dition. 


ELEMENTARY  PARTS  OF  ANIMAL  STRUCTURES.  109 


CHAPTER  III. 

OF  THE  ELEMENTARY  PARTS  OF  ANIMAL  STRUCTURES. 

162.  In  the  investigation  of  the  operations  of  a  complex  piece  of 
Mechanism,  and  in  the  study  of  the  forces  which  combine  to  produce 
the  general  result,  experience  shows  the  advantage  of  first  examining 
the  component  parts  of  the  Machine, — its  springs,  wheels,  levers, 
cords,  pulleys,  &c., — determining  the  properties  of  their  materials, 
and  ascertaining  their  individual  actions.  When  these  have  been 
completely  mastered,  the  attention  may  be  directed  to  their  combined 
actions;  and  the  bearing  of  these  combinations  upon  each  other,  so 
as  to  produce  the  general  result,  w^ould  be  the  last  object  of  study. 

163.  This  seems  the  plan  which  the  Student  of  Physiology  may 
most  advantageously  pursue,  in  the  difficult  task  of  making  him'self 
acquainted  with  the  operations  of  the  living  fabric,  and  with  the  mode 
in  which  they  concur  in  the  maintenance  of  Life.  He  should  first 
examine  the  properties  of  the  component  materials  of  the  structure 
in  their  simplest  form  ;  these  he  will  find  in  its  nutrient  fluids.  He 
may  next  proceed  to  the  simplest  forms  of  organized  tissue,  which 
result  from  the  mere  solidification  of  those  materials,  and  whose  pro- 
perties are  chiefly  of  a  mechanical  nature.  From  these  he  will  pass 
to  the  consideration  of  the  structure  and  vital  actions  of  those  tissues 
that  consist  chiefly  of  cells;  and  will  investigate  the  share  they  take 
in  the  various  operations  of  the  economy.  Next  his  attention  will 
be  engaged  by  the  tissues  produced  by  the  transformation  of  cells  ; 
of  which  some  are  destined  chiefly  for  affording  mechanical  support 
to  the  fabric,  and  others  for  peculiar  vital  operations.  And  he  will 
be  then  prepared  to  understand  the  part,  which  these  elementary  tis- 
sues severally  perform  in  the  more  complex  organs.  A  due  know- 
ledge of  these  elementary  parts,  and  of  their  physical,  chemical,  and 
vital  properties,  is  essential  to  every  one  who  aims  at  a  scientific 
knowledge  of  Physiology.  True  it  is,  that  we  may  study  the  results 
of  their  operations,  without  acquaintance  with  them ;  but  we  should 
know^  nothing  more  of  the  worldng  of  the  machine,  than  we  should 
know  of  a  cotton-mill,  into  which  we  saw  cotton-wool  entering,  and 
from  which  we  saw  woven  fabrics  issuing  forth ;  or  of  a  paper-mak- 
ing-machine, which  we  saw  fed  at  one  end  with  rags,  and  discharg- 
ing hot-pressed  paper,  cut  into  sheets,  at  the  other.  The  study  of 
these  results  affords,  of  course,  a  very  important  part  of  the  know- 
ledge we  have  to  acquire  respecting  the  operations  of  the  machine  ; 
but  we  could  learn  from  them  very  little  of  the  nativre  of  the  separate 
processes  effected  by  it ;  still  less  should  we  be  prepared,  by  any  dis- 
order or  irregularity  in  the  general  results,  to  seek  for,  and  rectify, 


110  ELEMENTARY  PARTS  OF  ANIMAL  STRUCTURES. 

the  cause  of  the  disturbance  in  the  working  of  the  machine,  by  which 
the  abnormal  result  was  occasioned. 

164.  Now  just  as  in  a  Cotton-mill,  there  are  machines  of  several 
different  kinds,  adapted  to  effect  different  steps  of  the  change,  by 
which  the  raw  material  is  converted  into  the  woven  fabric,  so  do  we 
find  that  in  the  complex  animal  fabric  there  is  a  great  variety  of  or- 
gans for  performing  the  several  changes,  by  which  the  fabric  itself  is 
built  up  and  maintained  in  a  condition  fit  for  the  performance  of  its 
peculiar  operations.  These  operations  are  the  phenomena  of  sensa- 
tion, of  spontaneous  motion,  and  of  mental  action.  They  are  the 
great  objects  of  .y3?iimaZ  existence ;  just  as  the  combination  of  ele- 
ments into  organic  substances,  that  are  to  furnish  the  materials  of  the 
Animal  fabric,  seems  to  be  the  great  purpose  of  Vegetative  Life.  The 
vital  phenomena  which  are  peculiar  to  Animals,  are  manifestations  of 
the  properties  of  certain  forms  of  organized  matter, — the  Nervous  and 
Muscular  tissues, — which  are  restricted  to  themselves  ;  just  as  those 
which  are  common  to  Animals  and  Plants,  are  effected  by  organized 
structures,  which  are  found  alike  in  both  kingdoms.  Here,  then,  w^e 
have  the  essential  distinction  between  these  kingdoms ; — namely  the 
presence  in  Animals  of  a  peculiar  apparatus,  and  the  consequent 
possession  by  them  of  peculiar  endowments,  which  are  totally  wanting 
in  Plants.  In  the  lowest  forms  of  Animal  life,  we  are  obliged  to  infer 
the  presence  of  the  characteristic  structure,  from  the  obvious  exist- 
ence of  the  peculiar  endowments  ;  the  minuteness  of  their  entire  fabric 
being  such,  as  to  prevent  the  discovery  of  distinct  muscular  and 
nervous  fibres.  But  there  are  many  species,  indeed  whole  tribes,  in 
which  it  is  impossible  to  say  with  certainty,  how  far  sensibility  and 
spontaneity  of  action  may  be  justly  inferred  from  the  movements  they 
exhibit ;  and  as  other  distinguishing  characters  are  deficient,  it  is 
undetermined  (and  perhaps  will  ever  remain  so)  to  which  kingdom 
they  ought  to  be  assigned. 

165.  All  the  operations,  then,  which  are  common  to  Animals  and 
Plants,  are  concerned  in  the  building-up  of  the  organized  fabric,  in 
the  maintenance  of  its  integrity,  and  in  the  preparation  of  the  germs 
of  new^  structures,  to  compensate  for  the  loss  of  the  parent  by  death. 
These  operations,  as  formerly  explained  (§  44),  involve  a  series  of 
very  distinct  processes ;  which,  although  all  performed  by  the  simple 
cell  of  the  humblest  plant,  are  distributed  in  more  complex  structures 
through  a  number  of  parts  or  organs ;  whose  several  actions  are  almost 
as  separate  as  those  of  the  dissimilar  machines  of  the  cotton-mill, — 
although,  like  them,  sustained  by  the  same  powers,  and  so  far  mutu- 
ally dependent,  that  neither  of  them  can  be  suspended  without  in  a 
short  time  putting  a  stop  to  the  rest.  Now  just  as  in  each  of  the 
machines  of  the  cotton-mill  we  may  have  similar  elements, — such  as 
wheels,  levers,  pulleys,  bands,  &c., — put  together  in  different  me- 
thods, and  consequently  adapted  for  different  purposes,  as  carding, 
spinning,  weaving,  &c,,  so  shall  we  find  in  the  animal  body,  that 
these  different  organs  are  composed  of  very  similar  elements,  and  that 


ELEMENTARY  PARTS  OF  ANIMAL  STRUCTURES.  HI 

the  individual  actions  of  these  elementary  parts  are  the  same  ;  but  that 
the  difference  of  result  is  the  consequence  of  the  variety  in  their 
arrangement.  Thus  we  shall  find  that  the  growth  of  cells,  their  ab- 
sorption of  certain  matters  from  the  surrounding  fluids,  and  their  sub- 
sequent liberation  of  these  by  the  bursting  or  liquefying  of  the  cell-wall 
Avhen  their  term  of  life  is  come  to  an  end,  are  means  employed  in  one 
part  of  the  body  to  introduce  nutrient  materials  into  the  current  of  the 
circulation,  whilst  in  another  the  same  processes  are  used  as  means 
to  withdraw,  from  that  very  same  current,  certain  substances  of  which 
it  is  necessary  to  get  rid.  Now  certain  combinations  of  elementary 
structure,  adapted  to  the  performance  of  a  set  of  actions  tending  to 
one  purpose,  and  thus  resembling  one  of  the  machines  of  a  cotton- 
mill,  is  termed  an  organ;  and  the  sum-total  of  its  actions  is  termed  its 
function.  Thus  w^e  have  in  the  function  of  Respiration,  which  essen- 
tially consists  of  an  interchange  of  oxygen  and  carbonic  acid  between 
the  air  and  the  blood,  a  multiiude  of  distinct  changes,  some  of  them 
of  a  character  apparently  not  in  the  least  related  to  it,  but  all  neces- 
sary, in  the  higher  and  more  complex  fabric,  to  bring  the  blood  and 
the  air  into  the  necessary  relation.  The  sum-total  of  these  changes 
constitutes  the  function  of  Respiration  ;  and  the  structures  by  which 
they  are  effected  are  organs  of  Respiration. 

166.  The  whole  organized  structure,  then,  may  be  regarded  as 
made  up  of  distinct  organs^  having  their  several  and  (to  a  certain  ex- 
tent) independent  purposes ;  and  these  organs  may  be  resolved,  in  like 
manner,  into  simple  elementary  parts,  whose  structure  and  composi- 
tion are  the  same,  in  whatever  part  of  the  fabric  they  occur.  And  in 
like  manner,  the  phenomena  of  Life,  considered  as  a  whole,  may  be 
arranged  under  several  groups  or  functions,  according  to  the  imme- 
diate purpose  to  which  they  are  directed  ;  and  yet  in  every  one  of 
these  groups,  we  shall  find  repeated  the  same  elementary  changes 
which  are  concerned  in  the  rest.  Thus  in  the  act  of  Respiration,  the 
same  kind  of  muscular  movements,  the  same  sort  of  nervous  agency, 
are  concerned,  as  contribute  to  the  ingestion  of  the  food  ;  and  a  simi- 
lar circulation  of  the  blood,  to  that  which  supplies  the  materials  for 
the  nutrition  of  the  tissues.  Hence  we  see  the  propriety  of  applying 
ourselves  first  to  the  consideration  of  the  elementary  parts  of  the  living 
structure,  and  of  the  properties  by  which  they  effect  the  changes, 
that  are  characteristic  of  its  several  organs. 

1.    Of  the  original  Components  of  the  Animal  Fabric. 

167.  As  we  can  best  study  the  original  Components  of  the  Animal 
Fabric,  by  investigating  their  properties  before  the  process  of  Organi- 
zation begins,  or  whilst  it  is  taking  place,  we  must  have  recourse  for 
this  purpose  to  the  nutrient  fluid, — the  Blood, — in  which  these  are 
contained  in  the  state  most  completely  prepared  for  the  reception  of 
the  Vitalizing  influence.  The  same  substances  may  be  found,  in  an 
earlier  stage  of  preparation,  in  the  Chyle  and  Lymph  ;  and  also  in  the 


112  PROTEINE-COMPOUNDS. 

Eggs  of  oviparous  animals.  The  circumstances  attending  the  develop- 
ment of  the  latter  afford,  indeed,  the  most  satisfactory  proof  of  the 
convertibility  of  the  simple  chemical  product.  Albumen,  with  certain 
inorganic  substances,  into  every  form  of  organized  structure.  For  the 
white  of  the  egg  consists  of  nothing  else  than  albumen,  combined  with 
phosphate  of  lime  ;  whilst  the  yetk  is  chiefly  composed  of  the  same 
substance,  mingled  with  oily  matter,  and  a  minute  quantity  of  sul- 
phur, iron,  and  some  other  inorganic  bodies.  Yet  this  albumen  and 
fatty  matter  are  converted  by  the  germ,  after  the  lapse  of  a  few  days, 
under  the  simple  stimulus  of  an  elevated  temperature,  into  a  complex 
fabric,  composed  of  bones,  muscles,  nerves,  tendons,  ligaments,  car- 
tilages, fibrous  membranes,  fat,  cellular  tissue,  &c.  &c.,  and  endowed 
with  the  properties  characteristic  of  all  these  substances,  which,  when 
brought  into  consentaneous  activity,  manifest  themselves  in  the  Life 
of  the  chick.  In  tracing  these  wonderful  transformations,  therefore, 
we  should  rightly  commence  with  Albumen.  But  as  recent  Chemical 
researches  have  shown,  that  this  may  be  considered  as  a  compound 
of  the  more  simple  substance  termed  Proteine,  with  Phosphorus  and 
Sulphur,  and  as  its  relations  to  the  compounds  formed  in  Vegetable 
growth  are  thereby  rendered  more  apparent,  it  will  be  desirable  to 
commence  with  the  latter,  which  has  been  truly  said  to  be  the  most 
universally-present,  and  most  important  to  life,  of  all  the  substances 
known  to  the  Organic  Chemist. 

168.  Proteine  may  be  detected  in  almost  every  part  of  the  Vegeta- 
ble as  well  as  of  the  Animal  fabric,  in  various  conditions  and  states 
of  combination  ;  being  found  in  a  soluble  form  in  their  fluids,  and  in 
an  insoluble  state  in  their  solid  parts.  It  may  be  obtained  by  dissolv- 
ing boiled  Albumen  in  a  weak  solution  of  caustic  alkali;  and  by  then 
neutralizing  the  liquid  by  an  acid,  which  causes  its  precipitation  in 
the  form  of  grayish-white  flocks.  And  it  may  also  be  obtained  from 
the  Gluten  of  wheat  flour  (the  substance  which  is  left  when  dough  is 
washed  with  w^ater  so  as  to  separate  the  starch  from  it),  by  the  very 
same  process.  After  being  washed,  it  is  gelatinous,  of  a  grayish 
colour,  and  semi-transparent ;  when  dried,  it  is  yellowish,  hard,  easily 
pulverized,  tasteless,  insoluble  in  water  and  alcohol,  and  decomposed 
by  heat- without  fusing.  There  is  no  perceptible  difference,  either 
in  elementary  composition,  or  in  chemical  relations  with  other  sub- 
stances, between  the  two  specimens  of  Proteine  thus  obtained  by  the 
same  process  from  the  Animal  and  Vegetable  kingdoms.  They  are 
both  composed,  according  to  Mulder,  of  40  Carbon,  31  Hydrogen,  5 
Nitrogen,  and  12  Oxygen  ;*  they  are  rendered  soluble  by  alkalies, 
and  are  precipitated  again  by  acids  ;  and  they  form  with  the  latter  and 
with  oxygen,  definite  chemical  compounds,  from  which  the  combining 
equivalent  just  stated  is  determined.     Proteine  unites  also  with  Sul- 

*  The  formula  of  Liebig  is  different ;  being  48  Carbon,  36  Hydrogen,  6  Nitrogen, 
14  Oxygen.  That  of  Mulder  agrees  equally  well  with  the  proportions  of  the  elements, 
as  deduced  from  analysis;  and  seems  to  represent  more  accurately  the  combining 
equivalent  of  this  substance. 


PROTEINE-COMPOUNDS.  113 

phur  and  Phosphorus,  in  various  proportions ;  and  it  is  never  found 
free  from  these,  or  in  a  simple  uncombined  state. 

169.  The  azotized  substances  obtained  from  Plants,  which  have 
received  the  names  of  Vegetable  Albumen^  Vegetable  Fibrin,  and 
Vegetable  Casein,  are  all  compounds  of  proteine  with  the  last-named 
elements;  but  the  exact  amount  of  the  latter  has  not  been  certainly 
ascertained  in  each  case ;  the  proportion  they  bear  to  the  proteine 
being  so  small,  as  to  render  the  analysis  difficult.  These  proteine- 
compounds  are  found  in  the  youngest  parts  of  the  roots  of  plants;  and 
are  probably  formed  there,  and  transported  by  the  circulation  of  the 
sap  into  distant  parts.  The  milk-white  colour  of  certain  vegetable 
juices  is  partly  due  to  the  large  quantity  of  these  substances  which 
they  contain.  The  deposition  of  the  proteine-compounds  in  certain 
groups  of  cells,  in  a  solid  condition,  would  be  sufficiently  accounted 
for  by  the  agency  of  an  acid,  which  changes  it  from  its  soluble  to  its 
insoluble  form ;  whilst,  on  the  other  hand,  its  removal  from  one  set 
of  cells,  and  its  transference  to  others,  might  be  accomplished  by  an 
alkaline  solution,  which  would  re-dissolve  it.  That  such  a  transference 
really  does  take  place,  appears  from  the  fact,  that  the  proportion  of 
the  proteine-compounds  contained  in  old  cells  is  much  less  than  that 
of  the  young  and  growing  parts;  from  which,  therefore,  it  seems  to 
be  removed  at  a  subsequent  time.  The  principal  differences  in  the 
properties  of  the  three  compounds  above  named  are  these.  Vegetable 
Albumen,  and  Legurain  or  Vegetable  Casein,  are  both  of  them  solu- 
ble in  cold  water;  but  the  former  is  coagulated  by  heat,  and  may  be 
obtained  in  this  manner  from  the  fresh  saps  of  most  plants ;  whilst  the 
latter  is  not  coagulated  by  heat,  but  may  be  precipitated  by  acids  from 
water  in  which  the  meal  of  peas  or  beans  has  been  soaked.  The 
substance  termed  Vegetable  Fibrin,  or  more  correctly  Coagulated 
Vegetable  Albumen,  is  insoluble  in  water ;  and  is  the  azotized  matter 
existing  in  the  seeds  of  corn,  in  almonds,  &c.,  which  is  not  taken  up 
by  water.  Besides  these,  there  is  another  termed  glutin  to  be  obtained 
from  wheat  flour,  by  the  agency  of  alcohol,  in  which  it  is  soluble. 

170.  It  is  certain  that  the  proteine-compounds  of  Plants  are  trans- 
ferred into  the  bodies  of  Animals,  and  become,  with  little  or  no  change, 
the  materials  of  their  organizing  processes.  Whether  similar  com- 
pounds may  be  formed  within  the  animal  body,  at  the  expense  of  any 
of  the  other  materials  supplied  by  plants,  has  not  yet  been  certainly 
ascertained ;  but  the  preponderance  of  evidence  appears  on  the  nega 
tive  side.  According  to  Mulder,  the  proportions  in  which  Sulphur 
and  Phosphorus  are  united  with  Proteine,  in  the  Animal  body,  are  as 
follows  : — in  the  Albumen  of  blood-serum,  2  Sulphur,  and  1  Phospho- 
rus, to  10  Proteine; — in  Fibrin  and  the  Albumen  of  eggs,  1  Sulphur, 
and  1  Phosphorus,  to  10  Proteine; — in  Casein,  1  Sulphur  to  10  Pro- 
teine;— and  in  the  substance  of  which  the  Crystaline  lens  of  the  eye 
is  chiefly  made  up,  1  Sulphur  to  10  Proteine.  The  small  proportion 
of  the  additional  elements  is  no  argument  against  their  being  of  great 
importance  in  the  constitution  of  these  bodies  ;  for  Inorganic  Chemistry 

8 


114  PROTEINE-COMPOUNDS. 

furnishes  numerous  examples,  in  which  the  presence  or  absence  of  a 
body  that  bears  a  very  small  proportion  to  the  whole,  makes  a  vast 
difference  in  the  properties  of  the  compound.  Thus  Arseniuretted 
Hydrogen,  which  is  one  of  the  most  poisonous  of  all  gases,  contains 
less  than  2  per  cent,  of  Hydrogen;  yet  it  is  to  this  small  quantity,  that 
the  peculiar  character  and  gaseous  state  of  this  compound  are  owing. 
Still  more  remarkable  is  the  fact  mentioned  by  Sir  J.  Herschel,  that 
by  alloying  mercury  with  a  millionth  of  its  weight  of  sodium,  a  power 
of  not  less  than  50,000  times  that  of  gravity  is  instantaneously  gene- 
jated,  when  the  alloy  is  submitted  to  galvanic  influence. — It  cannot 
be  doubted,  however,  from  considerations  presently  to  be  stated,  that 
«  far  greater  diflerence  exists  between  animal  Albumen  and  animal 
Fibrin^  than  between  any  of  the  corresponding  principles  in  Plants  ; 
«nd  that  this  difference  is  due  much  less  to  diversity  in  composition 
(for  according  to  Mulder,  the  amount  of  all  the  components  is  the 
•same  in  the  Fibrin  of  blood  and  in  the  Albumen  of  the  egg),  than  to 
« -change  in  the  arrangement  of  the  ultimate  particles. 

171.  According  to  Mulder,  Proteine  unites  with  Oxygen  in  definite 
proportions,  so  as  to  form  a  binoxide  and  a  tritoxide.  These  are  both 
produced  when  Fibrin  is  boiled  in  water  for  some  time  ;  the  latter 
being  then  found  dissolved,  whilst  the  former  remains  insoluble.  The 
tritoxide  may  also  be  formed  by  boiling  Albumen  for  some  time  in 
water,  and  is  in  like  manner  taken  up  in  solution  ;  but  the  insoluble 
residue  is  still  albumen.  It  is  further  obtainable  by  decomposing  the 
chlorite  of  proteine  with  ammonia.  In  its  properties  it  somewhat 
resembles  gelatin,  and  has  been  mistaken  for  that  substance.  There 
is  reason  to  think  that  this  compound  really  exists  as  such  in  the 
blood  ;  a  small  quantity  of  it  being  formed  every  time  that  the  blood 
passes  through  the  lungs,  and  given  out  again  when  it  returns  to  the 
system  ;  and  a  much  larger  amount  being  generated  during  the  in- 
flammatory process,  so  that  it  may  be  easily  obtained  from  the  "  buffy 
coat"  by  boiling.  It  is  also  contained  in  pus,  which  is  a  product  of 
the  inflammatory  process. — The  binoxide  is  quite  insoluble  in  water, 
but  dissolves  in  dilute  acids.  It  may  be  obtained  by  dissolving  hair  in 
potash,  adding  a  little  acid  to  throw  down  the  proteine,  and  then 
adding  a  large  excess  of  acid,  which  precipitates  the  binoxide.  Ac- 
cording to  Mulder,  this  compound  also  is  produced  in  small  quantity 
at  every  respiration;  and  it  enters  into  the  normal  composition  of 
several  of  the  animal  tissues.  These  views,  however,  must  still  be 
received  with  some  hesitation. 

172.  One  of  the  most  characteristic  and  important  properties  of 
Proteine,  is  the  facility  with  which  it  undergoes  decomposition,  when 
acted  on  by  other  chemical  substances,  especially  by  alkalies.  If  a 
proteine-compound  be  brought  into  contact  with  an  alkali,  ammonia 
is  immediately  disengaged  ;  indeed,  the  alkaline  solution  can  hardly  be 
made  weak  enough  to  prevent  the  disengagement  of  ammonia.  This 
is  a  property,  which  must  be  continually  acting  in  the  living  body ; 
since  the  blood  has  a  decided  alkaline  reaction.     If  either  albumen, 


PROTEINE-COMPOUNDS.— ALBUMEN.  •     115 

or  any  other  proteine-compound,  be  boiled  with  potash,  it  is  com- 
pletely decomposed  ; — not,  however,  being  resolved  at  once  into  its 
ultimate  constituents,  or  altogether  into  simple  combinations  of  them, 
but  in  great  part  into  three  other  organic  compounds,  Leucin,  Protid, 
and  Erythroprotid. — Leucin  is  a  crystaline  substance,  which  forms 
colourless  scales,  destitute  of  taste  and  odour  ;  it  is  soluble  in  water 
and  alcohol,  and  sublimes  unchanged.  It  consists  of  12  Carbon,  12 
Hydrogen,  1  Nitrogen,  and  4  Oxygen.  There  is  not  at  present  any 
evidence  that  it  is  produced  in  the  living  body;  and  the  chief  interest 
which  attaches  to  it  arises  from  the  fact,  that  it  may^be  procured  from 
Gelatin  as  well  as  from  Proteine  ;  which  indicates  a  near  relationship 
between  these  two  substances. — The  two  other  compounds,  Protid 
and  Erythroprotid^  are  uncrystaline  substances,  the  former  of  a  straw- 
yellow,  and  the  latter  of  a  reddish-brown  colour  ;  they  belong  to  the 
class  of  bodies  which  was  formerly  included  under  the  vague  general 
term  of  extractive  matter;  and  both  in  their  chemical  composition, 
and  their  solubility  in  water,  they  bear  a  strong  resemblance  to  Gela- 
tin. The  first  of  them  consists  of  13  C,  9  H,  1  N,  4  O  ;  and  the 
second  of  13  C,  8  H,  1  N,  5  0  ;  whilst  the  formula  of  Gelatin  is  13 
C,  10  H,  2  N,  5  O. — Besides  these  substances,  Ammonia,  with  Formic 
and  Carbonic  Acids,  are  produced ;  the  acids  unite  w^ith  the  potash, 
employed  to  effect  the  decomposition  ;  and  the  ammonia  is  set  free. 

173.  We  have  next  to  speak  of  that  one  of  the  proteine-compounds 
in  the  living  body,  which  corresponds  most  closely  with  those  yielded 
by  Plants,  and  which  serves  as  the  material  at  the  expense  of  which 
all  the  rest  may  be  formed,  by  chemical  transformations  analogous  to 
the  preceding.  This  is  Mbumen ;  which  exists  in  solution  in  the 
Blood  and  Chyle  ;  and  which  makes  up  the  largest  part  of  the  yelk, 
and  the  whole  of  the  white,  of  the  Egg.  In  its  soluble  state,  it  is 
always  combined  with  a  small  quantity  of  free  soda,  with  which  it 
seems  to  be  united  as  an  acid  with  its  base  ;  and  to  this  state  of  com- 
bination, its  solubility  is  regarded  by  most  Chemists  as  being  due. 
When  the  fluid  in  w^hich  it  is  dissolved  is  evaporated  at  a  low  tem- 
perature (not  exceeding  126°),  the  Albumen,  or  rather  Albuminate  of 
Soda,  maybe  dried,  without  losing  its  solubility  ;  when  dried,  it  may 
be  exposed  to  a  temperature  of  212°,  without  undergoing  change  ; 
and  it  forms,  when  again  dissolved  in  water,  the  same  glairy,  colour- 
less, and  nearly  tasteless  fluid  as  before.  When  a  higher  temperature 
is  employed,  however,  the  Albumen  passes  into  the  insoluble  form  ; 
and  presents  itself  either  as  a  cloudy  or  flocculent  precipitate,  or  as  a 
firm  consistent  coagulum,  according  to  the  strength  of  the  original 
solution.  The  same  condition  regulates  the  amount  of  heat  requisite 
for  the  purpose  ;  thus  if  the  quantity  of  albumen  be  so  great  that  the 
liquid  has  a  slimy  aspect,  a  temperature  of  145°  or  150°  is  suflScient 
for  the  purpose,  and  the  whole  becomes  solid,  white,  and  opaque  ; 
but  in  a  very  dilute  condition,  boiling  is  required,  and  the  albumen 
then  separates  in  the  form  of  white  finely-divided  flocks.  In  either 
case,  the  soda,  and  other  soluble  salts  are  separated  from  the  albumen. 


116     '  ALBUMEN;   CASEIN. 

and  remain  dissolved  in  the  water.  When  the  coagulation  of  Albu- 
men takes  place  rapidly,  the  coherent  mass  seems  quite  homogeneous, 
and  shows  no  trace  of  anything  like  definite  arrangement ;  hut  when 
the  process  is  more  gradual,  minute  granules  present  themselves, 
which  do  not,  however,  exhibit  a  tendency  towards  any  higher  form 
of  structure.  The  insoluble  coagulum,  or  pure  Albumen,  dries  up  to 
a  yellow,  transparent,  horny  substance  ;  which,  when  macerated  in 
water,  resumes  its  former  whiteness  and  opacity. — Pure  Albumen 
may  also  be  obtained  from  the  solid  mass,  which  remains  when  an^ 
Albuminous  fluid  is  dried  at  a  low  temperature,  by  reducing  it  to  a 
fine  powder,  and  then  washing  it  with  cold  water  on  a  filter  ;  common 
salt,  with  sulphate,  phosphate  and  carbonate  of  soda,  is  dissolved 
out ;  and  a  soft  swollen  mass  remains  upon  the  filter,  which  has  all 
the  characters  of  Albumen,  obtained  by  precipitation,  except  that  it  is 
readily  soluble  in  a  solution  of  nitrate  of  potash,  which  will  not  dis- 
solve the  latter  substance. 

174.  Albumen  may  also  be  thrown  down  from  its  solution,  in  a 
coagulated  state,  by  Alcohol,  Creasote,  and  by  most  Acids,  when 
these  are  added  in  excess,  so  as  to  do  more  than  neutralize  the  alkali. 
Nitric  acid  is  particularly  eflBcacious  in  occasioning  coagulation ;  on 
the  other  hand.  Acetic  acid,  and  common  or  tribasic  Phosphoric  acid 
do  not  precipitate  it,  these  acids  having  the  property  of  dissolving 
pure  Albumen.  In  the  precipitation  of  Albumen  by  an  Acid,  definite 
compounds  are  formed  between  the  two ;  in  which  the  Albumen  acts 
the  part  of  a  base.  On  the  other  hand,  as  already  remarked,  it  serves 
.as  an  acid  in  its  combinations  with  the  caustic  Alkalies,  and  is  held 
in  solution  by  them.  Most  of  the  metallic  salts,  as  those  of  copper, 
lead,  mercury,  &c.,  form  insoluble  compounds  with  albumen,  and 
thus  give  precipitates  with  its  solution ;  hence  the  value  of  white  of 
egg  as  an  antidote,  in  cases  of  poisoning  with  corrosive  sublimate. 
The  best  method  of  detecting  the  presence  of  soluble  albumen  in 
very  small  quantity,  is  to  boil  the  liquid,  and  add  nitric  acid;  if  tur- 
bidity is  then  produced,  the  existence  of  albumen  may  be  inferred. 

175.  The  existence  of  unoxidized  Sulphur  in  Albumen,  is  shown 
by  the  familiar  fact  of  the  blackening  of  a  silver  spoon  by  a  boiled 
egg;  which  is  due  to  the  formation  of  an  alkaline  Sulphuret  during 
the  coagulation.  A  very  important  property  of  soluble  Albumen  is 
its  power  of  uniting  with  Phosphate  of  Lime,  and  rendering  it  solu- 
ble; it  is  in  this  way,  that  the  consolidating  material  of  bones  is 
introduced  into  the  body.  About  two  per  cent,  of  this  salt  may  be 
separated  from  Albumen  in  its  coagulated  state. 

176.  Nearly  allied  to  Albumen  is  the  substance  termed  Casein, 
which  replaces  it  in  Milk;  and  this  is  worthy  of  notice  here,  because 
it  is  the  sole  form  in  which  the  young  Mammal  receives  Proteine  into 
its  body,  during  the  period  of  lactation.  Like  Albumen,  this  sub- 
stance may  exist  in  two  forms,  the  soluble,  and  the  insoluble  or 
coagulated ;  and  it  further  agrees  with  it,  in  requiring,  as  a  condition 
of  its  solubility,  the  presence  of  a  free  alkali,  of  which,  however,  a 


ALBUMEN;    CASEIN;    FIBRIN.  117 

very  small  quantity  suffices  for  the  purpose.  It  differs  from  Albumen, 
however,  in  this ;  that  it  does  not  coagulate  by  heat,  and  that  it  is 
precipitated  from  its  solution  by  Acetic  acid.  Casein  is  further  re- 
markable for  the  facility  with  which  its  coagulation  is  effected  by  the 
contact  of  certain  animal  membranes,  as  in  the  ordinary  process  of 
cheese-making.  This  change  is  considered  by  some  Chemists  to  be 
due,  however,  not  to  any  direct  action  of  the  membrane  upon  the 
casein,  but  to  its  influence  in  converting  some  of  the  milk-sugar  into 
lactic  acid,  which,  separating  the  alkali  of  the  casein,  will  occasion 
the  precipitation  of  the  latter.  The  only  difference  w^hich  can  be 
detected  between  Albumen  and  Casein,  in  regard  to  the  proportions 
of  their  elements,  consists  in  the  absence  of  Phosphorus  in  the  latter; 
but  this  can  scarcely  be  the  cause  of  the  foregoing  differences  in  their 
properties.  Casein  appears  to  surpass  Albumen  in  its  power  of  com- 
bining with  the  phosphates  of  lime  and  magnesia,  and  rendering  them 
soluble. 

177.  Albumen  and  Casein,  then,  may  be  regarded  as  constituting 
the  raw  materials,  at  the  expense  of  which  the  organized  tissues  of 
the  Animal  fabric  are  built  up  ;  and  w^e  have  sufficient  evidence,  in 
the  development  of  the  Chick  from  the  egg,  and  of  the  young  Mam- 
mal from  milk,  that  they  may  be  transformed  into  any  of  the  proteine 
compounds  which  are  to  be  found  in  the  Animal  body.  How  far  they 
may  require  to  be  united  with  fatty  matter  in  producing  some  of  these, 
— as  the  Nervous, — can  scarcely  be  yet  determined  ;  but  it  is  a  cir- 
cumstance worthy  of  note,  that  in  both  the  foregoing  cases,  fatty  mat- 
ter is  mingled  with  the  albumen,  in  the  aliment  destined  for  the 
development  of  the  young  animal.  The  purpose  of  this,  however, 
may  be  nothing  else  than  the  production  of  the  Adipose  tissue,  and 
the  maintenance  of  the  respiration. — Further  evidence  that  Albumen 
is  the  raw  material  of  the  Animal  tissues,  is  derived  from  this; — that 
it  is  the  form  to  which  all  the  proteine-compounds  contained  in  the 
food,  whether  derived  from  the  Animal  or  from  the  Vegetable  king- 
dom, are  reduced  by  the  Digestive  process;  and  in  which,  therefore, 
they  must  be  first  received  within  the  living  system. 

178.  We  find,  however,  in  the  fluids  that  are  formed  at  the  ex- 
pense of  this  Albumen  in  the  living  body,  namely  the  Chyle  and  the 
Blood,  another  substance  ;  which  is  so  closely  related  to  Albumen  in 
its  ultimate  Chemical  composition,  as  not  to  be  distinguishable  from 
it  with  any  degree  of  certainty;  but  w^hich  yet  differs  from  it  in  some 
of  its  chemical  properties,  and  still  more  in  the  tendency  w^hich  it  ex- 
hibits to  assume  the  organized  form  and  to  manifest  vital  properties. 
This  substance  is  named  Fibrin*  \i  is  found  in  the  Chyle  or  crude 
blood,  soon  after  it  is  drawn  from  the  food  ;  it  presents  itself  in  gradu- 

*  According  to  the  analyses  of  Dumas,  there  is  a  slight  difference  between  Fibrin 
and  Albumen  in  ultimate  composition;  the  former  having  less  Carbon,  aad  more 
Azote  than  the  latter.  The  difference,  however,  is  so  trifling,  that  it  may  be  doubted 
whether  the  Analytical  process  is  yet  sufficiently  certain  and  definite  to  substan- 
tiate it. 


118  FIBRIN. 

ally-increasing  proportion,  as  the  Chyle  slowly  passes  along  the 
Lacteal  vessels,  and  through  the  Mesenteric  glands,  towards  the  ter- 
mination of  the  Absorbent  system  in  the  Venous ;  and  it  is  also  found 
in  the  fluid  contents  of  that  other  division  of  the  Absorbent  system, 
the  Lymphatics,  which  is  distributed  through  the  body  at  large,  and 
Avhich  seems  to  have  for  its  chief  office  to  take  up,  and  to  re-introduce 
into  the  circulating  current,  such  particles  contained  in  the  fluids  of 
the  tissues,  as  do  not  require  to  be  at  once  cast  out  of  the  body,  but 
may  be  again  employed  in  the  process  of  Nutrition.  But  it  is  found, 
above  all,  in  the  Blood, — the  fluid  whose  ceaseless  and  rapid  course 
through  the  body  supplies  to  every  element  of  the  structure  the  mate- 
rials of  its  growth  and  development :  and  the  varying  proportions  in 
which  it  presents  itself  there,  are  evidently  closely  connected  with 
the  formative  powers  of  that  fluid.  It  is  also  a  principal  element  of 
certain  colourless  exudations^  which  are  poured  forth  from  wounded 
or  inflamed  surfaces,  or  which  are  deposited  in  the  interstices  of  in- 
flamed tissues;  these  exudations,  when  possessed  of  a  high  formative 
property  (that  is,  a  readiness  to  produce  an  organized  tissue),  are 
said  to  be  composed  of  coagulable  or  organizable  lymph,  which  is 
nothing  more  than  the  fibrinous  element  of  the  blood,  in  an  unusually 
concentrated  state.  We  shall  first  notice  the  Chemical  properties  of 
Fibrin  ;  and  shall  then  inquire  into  those,  which  present  the  first 
dawnings  or  indications  of  Vitality. 

179.  Like  the  other  Proteine-compounds,  Fibrin  may  exist  in  solu- 
tion, or  in  an  insoluble  form  ;  but  there  is  this  important  difference, — 
that  its  soluble  form  is  not  a  permanent  one,  and  cannot  be  maintained 
in  any  fibrinous  fluid  that  has  been  drawn  from  the  living  vessels, 
without  the  influence  of  re-agents,  w^hich  totally  destroy  its  peculiar 
properties.  All  investigations  of  a  Chemical  nature,  therefore,  must  be 
made  upon  insoluble  Fibrin;  and  this  may  be  obtained  in  its  purest 
state,  by  whipping  fresh  blood  with  a  bundle  of  twigs,  by  w^hich  opera- 
tion, it  will  i3e  caused,  in  coagulating,  to  adhere  to  the  twigs,  in  the 
form  of  long,  white,  elastic  filaments,  with  scarcely  an  admixture  of 
foreign  matter.  When  dried  in  vacuo,  or  at  a  gentle  heat,  it  becomes 
translucent  and  horny;  and  in  this  condition,  it  closely  resembles 
coagulated  albumen.  It  further  resembles  that  substance,  in  being 
soluble  in  very  dilute  caustic  alkali,  and  in  phosphoric  acid ;  and  the 
solutions  exhibit  many  of  the  properties  of  the  similar  solutions  of 
albumen.  When  the  fibrin  of  venous  blood  is  triturated  in  a  mortar 
with  a  solution  of  nitrate  of  potash,  and  the  mixture  is  left  for  twenty- 
four  hours  or  more  at  a  temperature  of  from  100°  to  120°,  it  becomes 
gelatinous,  slimy,  and  eventually  entirely  liquid.  In  this  condition,  it 
exhibits  all  the  properties  of  a  solution  of  Albumen  which  has  been 
neutralized  by  acetic  acid.  It  coagulates  by  heat ;  it  is  precipitated  by 
alcohol,  corrosive  sublimate,  &c.;  and,  when  largely  diluted,  it  deposits 
a  flocculent  substance,  not  to  be  distinguished  from  insoluble  albumen. 
The  close  Chemical  relation  of  Fibrin  and  Albumen  is  further  proved 
by  the  ready  conversion  of  the  former  into  the  latter  in  the  act  of  di- 


FIBRIN;    ITS  COAGULATION.  119 

gestion;  Animal  flesh,  which  consists  of  Fibrin,  being  reduced  to  the 
form  of  Albumen  with  the  same  facility  as  the  Vegetable  compounds, 
which  resemble  the  latter  much  more  closely  in  the  first  instance.  The 
Fibrin  of  arterial  blood,  however,  cannot  be  reduced  to  the  fluid  form 
by  solution  with  nitre ;  and  this  appears  to  be  due  to  the  oxidized 
condition  of  its  Proteine;  for  in  a  solution  of  Venous  fibrin  in  nitre,, 
contained  in  a  deep  cylindrical  jar,  and  having  its  surface  freely  ex- 
posed to  the  air,  a  fine  flocculent  precipitate  is  gradually  seen  to  form; 
and  this,  when  collected,  is  found  to  have  the  properties  of  arterial 
fibrin.  The  Fibrin  of  Animal  flesh  agrees  with  that  of  venous,  rather 
than  with  that  of  arterial  blood.  Fibrin,  like  Albumen,  unites  with 
acids  as  a  base,  forming  definite  compounds;  and  with  bases  as  an 
acid.  It  also  possesses  the  property  of  uniting  with  the  earthy  phos- 
phates; of  which  from  '7  to  2*5  per  cent,  are  found  in  the  ash  that  is 
left  after  its  combustion. 

180.  We  see,  then,  that  when  considered  in  its  simply-Chemical 
relations.  Fibrin  does  not  differ  in  any  essential  particular  from  Albu- 
men ;  and  that  the  chief  point  of  obvious  variation,  is  the  spontaneous 
coagulation  of  the  former,  when  it  is  removed  from  the  living  body. 
There  is,  however,  in  the  structure  of  the  coagulum  itself,  a  most  im- 
portant difference ;  for  instead  of  consisting  of  a  homogeneous  struc- 
tureless mass,  or  of  a  simple  aggregation  of  minute  granules,  it  is  found 
by  the  Microscope,  to  possess  a  definite ^6roM5  arrangement,  the  fibres 
crossing  one  another  in  every  direction.  In  the  ordinary  coagulum  or 
clot  of  Blood,  these  fibres  do  not  present  any  great  degree  of  firmness : 
they  may  be  hardened,  however,  by  boiling;  and  their  arrangement 
then  becomes  more  definite.  They  may  be  seen  much  more  clearly, 
however,  in  the  *'  huffy  coat"  of  Inflammatory  blood  ;  in  which  there 
is  not  only  an  increased  proportion  of  Fibrin,  but  the  Fibrin  itself 
seems  to  have  undergone  a  higher  elaboration, — that  is,  to  have  pro- 
ceeded still  further  in  the  change  towards  regular  organization.  In 
this  state,  the  process  of  coagulation  is  unusually  slow ;  the  clot  formed 
by  the  fibrous  tissue  is  much  more  solid ;  and  it  continues  for  some 
hours,  or  even  days,  to  increase  in  solidity,  by  the  mutual  attraction 
of  the  particles  composing  the  fibres,  which  causes  them  to  contract 
and  to  expel  the  fluid  contained  in  their  interstices. 

181.  The  most  perfect  fibrous  structure  originating  in  the  simple 
coagulation  of  fibrin  is  to  be  found,  however,  in  those  exudations 
which  take  place  either  from  inflammation,  or  from  a  peculiar  forma- 
tive action,  destined  to  repair  an  old  tissue  or  to  produce  a  new  one. 
Thus  in  Fig.  2  is  shown  the  fibrous  structure  of  a  false  membrane  formed 
by  the  consolidation  of  a  fibrinous  exudation  from  the  surface  of  an 
inflamed  peritoneum.  And  in  Fig.  3  is  displayed  a  similar  fibrous 
structure  (in  which,  however,  the  fibres  have  more  of  a  reticulated 
arrangement),  which  incloses  the  fluid  contents  of  the  egg,  and  enters 
into  the  composition  of  the  shell  itself.  As  the  ovum  (which,  at  the 
time  of  its  quitting  the  ovarium,  consists  of  the  yelk-bag  only)  passes 
along  the  oviduct  of  the  parent,  it  receives  its  coating  of  albuminous 


120 


FIBRILLATION  OF  FIBRIN. 


matter,  of  which  layer  after  layer  is  thrown  out  by  the  vessels  of  the 
oviduct.    When  a  sufficient  supply  has  thus  been  furnished,  it  appears 


Fig.  2. 


Fig.  3. 


Fibrous  structure  of  inflammatory  exudation 
from  peritoneum. 


Fibrous  membrane,  lining  the  egg-shell, 
and  forming  the  animal  basis  of  the  shell 
itself. 


that  fibrinous  instead  of  albuminous  matter  is  poured  forth ;  and  this, 
in  coagulating,  forms  a  very  thin  layer  of  fibrous  tissue,  which  en- 
velops the  albumen.  Layer  after  layer  is  gradually  added ;  and  at 
last,  by  the  superposition  of  these  layers,  that  firm  tenacious  mem- 
brane is  formed,  which  is  afterwards  found  lining  the  egg-shell.  The 
process  is  then  continued,  with  this  variation,  that  carbonate  of  lime 
is  also  secreted  from  the  blood  in  a  chalky  state ;  and  its  particles  lie 
in  the  interstices  of  the  fibrous  network,  and  give  it  that  solidity  which 
is  characteristic  of  the  shell.  If  they  be  removed  by  the  agency  of  a 
weak  acid,  or  if  the  bird  be  not  sufficiently  supplied  w^ith  lime  at  the 
time  of  laying,  the  outer  membrane  has  the  same  consistence  as  the 
inner ;  and  either  may  be  separated,  after  prolonged  maceration,  by 
dextrous  manipulation,  into  a  series  of  layers  of  a  fibrovis  matting 
like  that  represented  in  Fig.  3. 

182.  It  is  scarcely  possible  to  deny  to  such  a  tissue  the  designation 
of  an  organized  structure,  even  though  it  contains  no  vessels,  and 
may  not  participate  in  any  further  Vital  phenomena.  We  shall  here- 
after find,  that  a  tissue  presenting  very  similar  characters  forms  a 
large  part  of  the  Animal  fabric  ;  and  that  the  vessels  with  which  it  is 
copiously  supplied,  have  for  their  object  nothing  else  than  the  remo- 
val of  its  disintegrated  or  decaying  portions,  and  the  deposition  of  new 
matter  in  a  similar  form  (§  194).  In  the  production  of  new  parts, 
w^e  find  this  simple  fibrous  tissue  performing  the  important  function  of 
serving  as  a  matrix  or  bed  for  the  support  of  the  vessels ;  and  as,  by 
the  more  gradual  transformation  of  the  nutritive  materials  they  bring, 
new  and  more  permanent  tissues  are  formed,  the  original  one  gradu- 
ally undergoes  disintegration,  and  all  traces  of  it  are  in  time  lost.  This 
would  appear  to  be  the  history  of  the  Chorion  of  the  Mammalian 
ovum  ;  which  is  at  first  nothing  else  than  a  fibrous  unvascular  bag, 
formed  round  the  ovum  in  its  passage  through  the  Fallopian  tube, 


FIBRILLATION  OF  FIBRIN.  121 

precisely  after  the  manner  of  the  shell-membrane  of  the  Bird's  egg; 
but  which  is  afterwards  penetrated  by  vessels  proceeding  from  the 
embryo,  and  in  time  acquires  a  new  structure  (Chap.  XI.) 

183.  The  completeness  of  the  production  of  such  a  fibrous  tissue 
depends  in  part,  as  we  have  seen,  upon  the  degree  of  elaboration 
which  the  Fibrin  has  undergone  ;  but  in  great  part  also  upon  the 
nature  of  the  surface,  on  which  the  coagulation  takes  place.  Thus 
we  never  find  so  perfect  a  membrane  formed  by  the  consolidation  of 
the  Fibrin  out  of  the  living  body, — on  a  slip  of  glass  for  example, — 
as  when  it  takes  place  on  the  surface  of  a  living  membrane,  or  in  the 
interstices  of  a  living  tissue.  This  may  perhaps  be  accounted  for  by 
the  fact,  that  the  coagulation  takes  place  much  more  slowly  in  the 
latter  case  than  in  the  former ;  and  that  the  particles  may  thus  have 
more  time  to  arrange  themselves  in  the  definite  fibrillation^  which 
seems  to  be  their  characteristic  mode  of  aggregation : — ^just  as  crys- 
talization  takes  place  best  when  the  action  is  slow ;  and  as  a  substance, 
whose  particles  would  remain  in  an  amorphous  or  disunited  form  if 
too  rapidly  precipitated  from  a  solution,  may  present  a  most  regular 
arrangement  when  they  are  separated  from  it  more  slowly.  Of  this 
view  it  would  seem  to  be  a  confirmation,  that  the  most  perfect  fibril- 
lation out  of  the  body  is  usually  seen  in  those  cases,  in  which  coagu- 
lation takes  place  least  rapidly. 

184.  The  conditions  under  which  the  spontaneous  coagulation  of 
Fibrin  takes  place,  are  best  known  from  the  observation  of  that  pro- 
cess as  it  occurs  in  the  Blood;  and  although  this  fluid,  as  we  shall 
hereafter  see,  is  of  a  very  complex  nature,  yet  as  the  Fibrin  alone  is 
concerned  in  its  coagulation,  and  as  that  act  appears  to  take  place  in 
the  same  manner  as  if  no  other  substance  was  present,  there  appears  to 
be  no  objection  to  the  employment  of  the  phenomena  of  Blood-coagu- 
lation as  the  basis  of  our  account  of  the  properties  of  Fibrin. — There 
can  be  no  doubt,  from  Microscopical  observation  of  the  circulating 
Blood,  that  Fibrin  is  in  a  state  of  perfect  solution  in  the  fluid  ;  and 
in  this  condition  it  remains,  so  long  as  it  is  in  motion  in  the  living 
body.  That  its  fluidity,  however,  does  not  depend  only  upon  its 
movement,  is  evident  from  two  facts; — first,  that  no  kind  of  motion 
seems  effectual  in  preventing  the  coagulation  of  the  blood,  after  it  has 
been  drawn  from  the  vessels; — and  second,  that  a  state  of  rest  within 
the  living  body  does  not  immediately  produce  coagulation  ;  a  portion 
of  blood,  included  between  two  ligatures  in  a  living  vessel,  remain- 
ing fluid  for  a  long  time.  On  the  other  hand,  it  seems  certain  that 
the  state  of  vitality  of  the  parts  with  which  the  blood  is  in  contact, 
has  a  great  influence  in  preserving  its  fluidity ;  thus  it  has  been  found 
that,  if  the  Brain  and  Spinal  Cord  of  an  animal  be  broken  down,  and 
by  this  measure  the  vitality  of  the  body  at  large  be  lowered,  clots  of 
blood  are  formed  in  their  trunks  within  a  few  minutes.  Nevertheless, 
a  mass  of  blood  effused  into  a  cavity  of  the  living  body,  undergoes 
coagulation  almost  as  soon  as  it  would  in  a  dead  vessel;  but  this  may 
be  accounted  for  by  the  very  small  surface  which  is  in  contact  with 


122  COAGULATION  OF  FIBRIN. 

the  blood,  as  compared  with  the  mass  of  the  latter.  It  must  be  re- 
membered that  the  circulating  blood  is  continually  being  subdivided 
into  countless  streams ;  and  that  each  of  these  passes  through  the 
living  tissue,  in  such  a  manner  that  all  its  particles  are  in  close  rela- 
tion with  the  living  surface.  Moreover  it  is  probable  that  the  form 
of  matter  which  we  term  Fibrin  never  remains  long  in  that  condi- 
tion, in  the  ordinary  state  of  the  system  ;  being  continually  withdrawn 
by  the  nutritive  processes,  and  as  continually  reformed  from  the  Al- 
bumen, by  an  elaborating  action  hereafter  to  be  considered.  Hence 
we  may  regard  the  state  of  motion  through  living  vessels,  as  essen- 
tial to  the  permanent  continuance  of  fibrin  in  the  fluid  form. 

185.  The  length  of  time,  however,  during  which  Fibrin  may  re- 
main uncoagulated,  after  it  has  been  withdrawn  from  the  living  body, 
varies  according  to  various  conditions ;  some  of  which  are  not  well 
understood.  In  the  first  place,  as  already  remarked,  the  more  ela- 
borated and  more  concentrated  the  condition  of  the  Fibrin,  the  more 
slowly  does  it  usually  coagulate.  Thus  when  a  large  quantity  of 
blood  is  drawn  at  one  bleeding,  into  several  vessels,  that  w^hich 
flows  first  takes  the  longest  time  to  coagulate,  and  forms  the  firmest 
clot ;  whilst  that  which  is  last  drawn  coagulates  most  rapidly  and 
with  the  least  tenacity.  The  coagulation  is  accelerated  by  moderate 
heat,  and  retarded  by  cold;  but  it  is  not  prevented  even  by  extreme 
cold  ;  for  if  blood  be  frozen  immediately  that  it  is  drawn,  it  will  coa- 
gulate on  being  thawed, — thus  preserving  its  vitality,  in  spite  of  the 
freezing  process,  like  the  organized  structures  of  many  of  the  lower 
animals.  Again,  the  coagulation  is  accelerated  by  exposure  to  air  ; 
but  it  is  not  prevented,  though  it  is  retarded,  by  complete  exclusion 
from  it.  Various  Chemical  agents  retard  the  coagulation,  without 
preventing  it ;  this  is  the  case  especially  with  solutions  of  the  neutral 
salts.  The  coagulation  is  not  so  firm,  however,  or  the  fibrillation  so 
perfect,  after  the  use  of  these  ;  and  there  can  be  no  doubt  that  they 
modify  the  properties  of  the  fibrin  by  acting  chemically  upon  it. 

186.  After  remaining  in  this  condition  for  a  certain  length  of  time, 
the  Fibrin  undergoes  a  further  change,  which  is  evidently  the  result 
of  decomposition ;  the  coagulum  becomes  soft,  and  exhibits  appear- 
ances of  putrefaction.  This  takes  place  the  more  rapidly,  as  the  first 
coagulation  was  less  complete.  Thus  in  the  imperfectly-elaborated 
Fibrin  of  the  Chyle,  the  coagulum  is  sometimes  so  incomplete  that 
it  does  not  separate  itself  from  the  serum,  and  liquefies  again  in  half 
an  hour.  In  certain  states  of  disease,  the  solidifying  properties  of  the 
Fibrin  are  very  much  impaired  ;  so  that  it  soon  liquefies  and  decom- 
poses. In  these  cases,  there  is  scarcely  any  trace  of  the  characteristic 
fibrous  arrangement  of  the  particles. — On  the  other  hand,  the  fibrin- 
ous coagulum  of  inflamed  blood,  as  it  is  more  solid,  is  also  more  per- 
sistent, than  that  of  ordinary  blood  ;  and  the  greatest  persistency  of 
all  is  seen  in  the  fibrous  network  formed  by  exudation,  as  in  the  cases 
just  now  mentioned. 

187.  The  coagulating  power  of  Fibrin, — in  other  words,  its  pecu- 


SIMPLE  FIBROUS  TISSUES.  123 

liar  vital  property, — may  be  destroyed  by  various  causes  operating 
within  the  living  body;  so  that  the  blood  remains  fluid  after  death. 
These  may  be  classed  under  three  heads.  In  the  first  place,  the 
vitality  of  the  fibrin  may  be  destroyed  by  substances  introduced  into 
the  blood  from  without;  which  have  the  power  of  acting  in  the  man- 
ner of  ferments^  and  which  occasion  an  obvious  chemical  change  in 
its  condition.  This  is  the  case  in  the  severe  forms  of  Typhoid  fever, 
which  are  termed  malignant ;  and  especially  those  which  result  from 
the  contact  of  putrescent  matter,  as  Glanders,  Pustule  maligne,  &c. 
Secondly,  it  may  be  impaired  or  altogether  destroyed  by  morbid  ac- 
tions originating  in  the  system  itself,  and  depending  upon  irregular 
nutrition  or  imperfect  excretion ;  thus  the  blood  has  been  found  fluid 
after  death,  in  severe  cases  of  Scurvy  and  Purpura,  also  in  cases  of 
Asphyxia  (consequent  upon  the  retention  of  carbonic  acid  in  the 
blood),  and  in  the  bodies  of  over-driven  animals.  The  same  result 
may  follow,  Thirdly,  from  violent  shocks  or  impressions,  which  sud- 
denly destroy  the  vitality  of  the  whole  system  at  once;  these  maybe 
such  as  are  obviously  capable  of  producing  a  chemical  or  mechanical 
change,  as  in  the  case  of  death  by  Lightning  or  by  a  violent  Electrical 
discharge;  or  they  may  act  through  the  nervous  system,  in  a  manner 
not  yet  clearly  understood,  as  when  death  results  from  concussion  of 
the  brain,  from  a  blow  upon  the  epigastrium,  from  violent  mental 
emotion,  or  from  a  coup  de  soleil. — It  is  not  to  be  supposed  that  the 
non-coagulability  of  the  Blood  is  a  phenomenon  by  any  means  invari- 
able under  the  foregoing  circumstances  ;  but  it  has  been  occasionally 
observed  in  all  of  them.  We  must  not  mistake,  for  the  absence  of 
coagulating  power,  the  remarkable  retardation  of  the  act  of  coagula- 
tion which  sometimes  occurs.  Thus,  the  blood  is  occasionally  found 
in  a  fluid  condition  in  the  bodies  of  persons  that  have  been  dead  for 
some  days;  and  yet  when  withdrawn  from  the  vessels  it  coagulates. 
An  instance  has  been  lately  put  on  record,  in  which  blood  drawn 
from  a  patient  suffering  under  an  attack  of  pneumonia,  did  not  coagu- 
late for  fifteen  days,  but  then  formed  a  firm  clot,  and  was  a  month 
before  it  putrefied. 

2.   Of  the  Simple  Fibrous  Tissues. 

188.  A  large  part  of  the  Animal  fabric,  especially  among  the  higher 
classes  in  which  the  parts  have  the  greatest  amount  of  motion  upon 
one  another,  is  composed  of  tissues,  which  seem  as  if  they  consisted 
of  nothing  else  than  fibres,  of  the  simple  character  already  described, 
woven  together  in  various  ways,  according  to  the  purposes  they  are 
destined  to  serve.  These  fibres  are  altogether  different  from  those 
hereafter  to  be  described  as  constituting  the  Muscular  and  Nervous 
tissues,  and  must  not  be  confounded  with  them.  The  former  are  solid, 
and  possess  none  but  physical  properties  ;  the  latter  are  tubular,  and 
are  distinguished  by  their  peculiar  vital  endowments,  which  seem 
chiefly,  if  not  entirely,  to  reside  in  the  contents  of  the  tubular  fibre. 


124 


SIMPLE  FIBROUS  TISSUES. 


Fig.  4. 


Simple  fibrous  tissue ;   a 
tissue  ;  6,  tendinous  fibres. 


fibres  of  areolar 


The  simple  fibrous  tissues,  of  which  we  have  now  to  treat,  appear  to 

have  for  their  sole  office  in  the 
animal  body  to  bind  together  the 
other  elementary  parts  into  one 
whole,  without  uniting  them  so 
closely  as  to  render  them  immov- 
able; and  we  find  the  same  elements 
arranged  in  very  different  modes, 
according  to  the  purposes  they  are 
destined  to  fulfil.  Thus  in  the  TeTi- 
dons^  by  which  the  Muscles  are  con- 
nected with  the  Bones  and  impart 
motion  to  them,  the  only  property 
required  is  that  of  resisting  strain 
or  tension  in  one  direction ;  and  in 
these  we  find  the  fibres  disposed  in  a  parallel  arrangement,  passing 
continuously  in  straight  lines  between  the  points  of  attachment.  In 
the  Ligaments  which  connect  the  bones  together,  and  which  also  have 
for  their  purpose  to  afford  resistance  to  strain,  but  which  are  liable  to 
tension  in  a  greater  variety  of  directions,  we  find  bundles  of  fibres 
crossing  each  other  according  to  these  directions ;  and  in  some  in- 
stances we  find  the  ligaments  endowed  also  with  a  certain  degree  of 
elasticity.  The  structure  of  the  strong  Fibrous  Membranes^  which 
form  the  envelops  to  different  organs  and  bind  together  the  contained 
parts,  is  very  similar ;  each  of  these  membranes  being  composed  of 
several  layers  of  a  dense  network,  formed  by  the  interweaving  of 
bundles  of  fibres  in  different  directions.  In  the  Fibro- Cartilages,  we 
find  a  mixture  of  the  characteristic  structure  of  Ligament  with  that  of 
Cartilage  ;  bundles  of  fibres,  similar  to  those  which  constitute  the 
former,  being  disposed  among  the  cells  which  are  the  chief  organized 
constituents  of  the  latter.  In  certain  Fibro-Cartilages,  however,  these 
fibres  are  endowed  with  a  high  degree  of  elasticity. 

189.  These  two  qualities, — that  of  resistance  to  tension  without  any 
yielding, — and  that  of  resistance  combined  with  elasticity, — are  cha- 
racteristic of  two  distinct  forms  of  Fibrous  tissue,  the  Wliite  and  the 
Yellow.  The  White  Fibrous  tissue  presents  itself  under  various  forms  ; 
being  sometimes  composed  of  fibres  so  minute  as  to  be  scarcely  dis- 
tinguishable ;  and  sometimes  presenting  itself  under  the  aspect  of 
bands,  usually  of  a  flattened  form,  and  attaining  the  breadth  of 
l-500th  of  an  inch.  These  bands  are  marked  by  numerous  longitu- 
dinal streaks,  but  they  cannot  be  torn  up  into  minute  fibres  of  deter- 
minate size  ;  hence  they  must  be  regarded  as  made  up  of  an  aggrega- 
tion of  the  same  elements  as  those  which  may  become  developed  into 
separate  fibres.  The  fibres  and  bands  are  occasionally  somewhat 
wavy  in  their  direction.  This  tissue,  which  is  perfectly  inelastic,  is 
easily  distinguished  from  the  other  by  the  effect  of  Acetic  acid,  which 
swells  it  up  and  renders  it  transparent,  at  the  same  time  bringing  into 
view  certain  oval  corpuscles,  which  are  supposed  to  be  the  nuclei  of 


SIMPLE  FIBROUS  TISSUES. 


125 


the  cells  that  were  concerned  in  the  formation  of  the  tissue. — The 
Yelloto  Fibrous  tissue  exists  in  the  form  of  long,  single,  elastic,  branched 


Fig.  5. 


Fig.  6. 


Fasciculus  of  fibres  of  white  fibrous  tissue 
from  lateral  ligament  of  kiiee-jaijit. 


Yellow  fibrous  tissue  from  ligamentum, 
nuchae ;  a,  the  fibres  drawn  apart,  to  show 
their  reticulate  arrangement;  b,  the  fibres  in 
situ. 


filaments,  with  a  dark  decided  border;  which  are  disposed  to  curl 
when  not  put  on  the  stretch.  They  are  for  the  most  part  between 
l-5000th  and  l-10,000th  of  an  inch  in  diameter;  but  they  are  often 
met  with  both  larger  and  smaller.  They  frequently  anastomose,  so  as 
to  form  a  network,  as  shown  in  Fig.  6.  This  tissue  does  not  undergo 
any  change,  when  heated  with  acetic  acid.  It  exists  alone  (that  is, 
without  any  mixture  of  the  white),  in  parts  which  require  a  peculiar 
elasticity,  such  as  the  middle  coat  of  the  Arteries,  the  Chordae  Vocales, 
the  Ligamentum  Nuchae  (of  Quadrupeds),  and  the  Ligamenta  sub- 
flava ;  it  enters  largely  into  the  composition  of  certain  parts,  which 
are  commonly  regarded  as  Cartilaginous,  such  as  the  external  ear; 
and  it  is  also  a  principal  component  of  other  tissues  to  be  presently 
described. 

190.  These  tissues  are  very  different  in  Chemical  composition. 
Those  which  are  composed  of  the  White  fibrous  element, — namely, 
Tendons,  Ligaments,  &c. — are  almost  entirely  resolved  by  long  boil- 
ing into  the  substance  termed  Gelatin  or  Glue ;  and  this  is  also 
largely  obtained  from  the  skin,  and  from  Mucous  and  Serous  Mem- 
branes, into  which,  as  we  shall  presently  see,  that  element  enters 
largely.  The  composition  of  Gelatin  is  much  simpler  than  that  of 
the  Protein-compounds ;  so  far,  at  least,  as  regards  the  number  of 
atoms  of  its  several  elements ;  for  it  consists  (according  to  Mulder) 
of  13  Carbon,  10  Hydrogen,  2  Nitrogen,  5  Oxygen.  This  compo- 
sition is  the  same,  whether  the  Gelatin  be  obtained  from  isinglass, 
from  fibrous  membranes,  or  from  bones.  The  distinctive  characters 
of  Gelatin  are  its  solubility  in  warm  water,  its  coagulation  on  cooling 
into  a  uniform  jelly,  and  its  formation  of  a  peculiar  insoluble  com- 
pound with  Tannic  acid.  Gelatin  is  very  sparingly  soluble  in  cold 
water;  though  prolonged  contact  with  it  will  cause  the  Gelatin  to  swell 


126  SIMPLE  FIBROUS  TISSUES. 

up  and  soften.  Its  power  of  forming  a  jelly  on  cooling  is  such,  that  a 
solution  of  one  part  in  100  of  water  will  become  a  consistent  solid. 
And  its  reaction  with  Tannic  acid  is  so  distinct,  that  the  presence  of 
one  part  of  Gelatin  in  5000  of  water  is  at  once  detected  by  infusion 
of  Galls. — There  can  be  no  doubt  that  Gelatin  does  not  exist  ex- 
actly as  such  in  the  Fibrous  tissues ;  since  none  can  be  dissolved  out 
of  them  by  the  continued  action  of  cold  water,  and  it  usually  re- 
quires the  prolonged  action  of  hot  water,  to  occasion  their  complete 
conversion.  There  are  some  substances,  however,  in  which  this  is 
not  requisite;  and  from  which  the  gelatin  may  be  more  readily  ex- 
tracted. This  is  the  case,  for  example,  with  the  air-bladder  of  the 
Cod  and  other  fish  ;  which,  when  cut  into  shreds  and  dried,  is  known 
as  Isinglass.  It  is  the  case  also  with  the  substance  of  bones,  from 
which  the  calcareous  matter  has  been  removed.  In  both  instances 
it  would  seem  that  the  state  of  organization  is  very  imperfect;  scarcely 
any  traces  of  the  fibrous  structure  being  perceptible.  When  the 
fibrous  arrangement  is  more  complete,  the  solubility  of  the  tissue  is 
much  diminished.  Hence  it  would  seem  that  the  particles  have  a 
different  arrangement  in  the  tissues,  from  that  w^hich  they  have  in  the 
product  obtained  by  boiling.  Their  ultimate  composition,  however, 
is  the  same ;  for  w^hen  any  serous  membrane,  or  other  tissue  princi- 
pally composed  of  the  w^hite  fibrous  element,  is  analyzed  by  combus- 
tion, the  elements  are  found  to  have  the  same  proportion  to  each 
other  as  in  Gelatin,  allowance  being  made  for  the  small  admixture 
of  other  substances.  The  action  of  Tannic  acid,  too,  is  the  same  on 
the  organized  tissue,  as  it  is  on  the  gelatin  extracted  from  it ;  and 
hence  results  its  utility  in  producing  an  insoluble  compound,  not 
liable  to  undergo  decomposition,  in  the  substance  of  the  skin,  con- 
verting it  into  leather. 

191.  It  is  not  yet  known  how  Gelatin  is  produced  in  the  Animal 
body.  There  can  be  no  doubt  that  it  may  be  elaborated  from  Albu- 
men ;  since  we  find  a  very  large  amount  of  Gelatin  in  the  tissues  of 
young  animals,  which  are  entirely  formed  from  albuminous  matter; 
and  also  in  the  tissues  of  herbivorous  animals,  which  cannot  receive  it 
in  their  food,  as  Plants  yield  no  substance  resembling  gelatin.  It 
has  been  suggested  by  Mulder,  that  Gelatin  may  be  formed  by  the 
decomposition  of  Protein,  which  has  been  already  mentioned  as  taking 
place  from  the  agency  of  weak  Alkaline  solutions,  (§  172,)  and  which 
must  probably,  therefore,  be  continually  occurring  in  the  blood. 
For  if  to  each  atom  of  Protid  and  Erythroprotid,  we  add  one  of  the 
atoms  of  Ammonia,  which  are  given  off  in  that  decomposition,  we 
have  compounds,  of  which  the  former  differs  from  Gelatin  only  by 
the  presence  of  two  additional  atoms  of  hydrogen  and  the  deficiency  of 
one  of  oxygen,  whilst  the  only  difference  in  the  latter  consists  in  the 
presence  of  one  additional  atom  of  hydrogen.  Thus  the  ammoniated 
erythroprotid,  when  exposed  to  oxygenation  in  the  lungs,  may  have 
its  one  superfluous  atom  of  hydrogen  carried  off  in  the  form  of  water, 
and  will  then  have  the  composition  of  Gelatin ;   and  the  same  result 


SIMPLE  FIBROUS  TISSUES.  127 

will  be  obtained  from  the  ammoniated  protid,  by  the  addition  of  three 
atoms  of  oxygen,  which  will  convert  it  into  gelatin  and  two  atoms 
of  water.  These  transformations  must  be  regarded  for  the  present  as 
altogether  theoretical;  but  it  does  not  appear  at  all  unlikely  that  they 
may  really  take  place. 

192.  The  composition  of  the  Yellow  fibrous  tissue  appears  to  be 
altogether  dissimilar.  It  scarcely  undergoes  any  change  by  prolonged 
boiling;  it  is  unaffected  also  by  the  weaker  acids;  and  it  preserves  its 
elasticity,  if  kept  moist,  for  an  almost  unlimited  period.  According 
to  Scherer  it  consists  of  48  Carbon,  38  Hydrogen,  6  Nitrogen,  and  16 
Oxygen ;  and  he  considers  it  to  be  composed  of  an  atom  of  Proteine 
with  two  atoms  of  water.  (See  §  168,  note.) 

193.  The  simple  Fibrous  tissues  appear  to  be  very  little  susceptible 
of  change  in  the  living  body;  and  we  find  them  very  sparingly 
supplied  with  blood-vessels.  In  the  solid  Tendons,  the  bundles  of 
straight  parallel  fibres  are  a  little  separated  from  each  other  by  the 
intervention  of  the  Areolar  tissue  to  be  presently  noticed ;  and  this 
permits  the  sparing  access  of  vessels  to  their  interior.  In  the  Fibrous 
Membranes  and  Ligaments,  this  is  found  in  somewhat  larger  amount; 
and  the  vascularity  of  these  tissues  is  rather  greater. 

194.  The  great  use  of  the  foregoing  Tissues  appears  to  be,  to  aflford 
a  firm  resistance  to  tension;  by  which  they  may  either  communicate 
motion,  as  in  the  case  of  Tendons ;  or  restrain  it,  as  in  the  case  of 
Ligaments ;  or  altogether  prevent  it,  as  in  the  case  of  Aponeuroses 
and  Fibrous  Membranes.  With  this  firm  resistance,  a  considerable 
amount  of  elasticity  may  be  combined.  But  we  have  now^  to  notice  a 
tissue,  in  which  a  very  different  arrangement  of  the  same  elements 
presents  itself;  and  the  object  of  this  is,  to  bind  together  the  elements 
of  the  different  fabrics  of  the  body,  and  at  the  same  time  to  endow 
them  with  a  greater  or  less  degree  of  freedom  of  movement  upon 
one  another.  This  tissue,  which  is  called  the  Areolar,  consists  of  a 
network  of  minute  fibres  and  bands,  which  are  interwoven  in  every 
direction,  so  as  to  leave  innumerable  areola  or  little  spaces,  which 
communicate  freely  with  one  another.  Of  these  fibres,  some  are  of 
the  yellow  or  elastic  kind  ;  but  the  majority  are  composed  of  the 
white  fibrous  tissue,  and,  as  in  that  form  of  elementary  structure,  they 
frequently  present  the  form  of  broad  flattened  bands,  or  membranous 
shreds,  in  which  no  distinct  fibrous  arrangement  is  visible.  The 
interstices  are  filled  during  life  with  a  fluid,  which  resembles  very 
dilute  serum  of  the  blood,  consisting  chiefly  of  water,  but  containing 
a  sensible  quantity  of  common  salt  and  albumen.  This  tissue, — 
which  has  been  frequently  but  erroneously  termed  Cellular, — is  very 
extensible  in  all  directions,  and  very  elastic,  from  the  structural 
arrangement  of  its  elements.  It  cannot  be  said  to  possess  any  dis- 
tinctly vital  endowments ;  for  although  it  has  a  certain  amount  of 
sensibility,  this  merely  depends  upon  the  presence  of  nerves  which  it 
is  conveying  to  other  parts ;  and  the  small   amount  of  contractility 


128  AREOLAR  TISSUES. 

which  it  shows,  depends  rather  upon  the  muscular  tissue  of  the  ves- 
sels that  traverse  it. 

195.  As  already  mentioned,  we  find  this  tissue  in  almost  every 
part  of  the  body  ;  thus  it  binds  together  the  ultimate  fibres  of  the 
Muscles  into  minute  fasciculi,  unites  these  fasciculi  into  larger  ones, 
these  again  into  larger  ones  which  are  obvious  to  the  eye,  and  these 
into  the  entire  muscle.  Again  it  forms  the  membranous  septa  between 
distinct  muscles,  or  between  muscles  and  fibrous  aponeuroses.  In  like 
manner  it  unites  the  elements  of  nerves,  glands,  &c. ;  binds  together 
the  fat-cells  into  minute  bags,  these  into  larger  ones,  and  so  on ;  and 
in  this  manner  penetrates  and  forms  a  considerable  part  of  all  the  softer 
tissues  of  the  body.  But  it  is  a  great  mistake  to  assert,  as  it  wais 
formerly  common  to  do,  that  it  penetrates  the  harder  organs,  such  as 
bones,  teeth,  cartilage,  &c.  Its  purpose  obviously  is,  to  allow  a  cer- 
tain degree  of  movement  of  the  parts  which  it  unites ;  and  hence  we 
find  it  entering  much  more  largely  into  the  composition  of  the  Mam- 
mary gland  (which,  from  its  attachment  to  the  great  pectoral  muscle, 
must  have  its  parts  capable  of  being  shifted  upon  one  another),  than 
into  that  of  the  Liver,  Kidneys,  &c.  It  also  serves  as  the  bed,  in 
which  blood-vessels,  nerves,  and  lymphatics  may  be  carried  into  the 
substance  of  the  different  organs ;  and  it  often  undergoes  a  degree  of 
condensation,  in  order  to  form  a  sheath  for  the  larger  trunks,  which 
gives  it  almost  the  characters  of  a  Fibrous  Membrane. 

196.  The  quantity  of  fluid  in  the  insterstices  of  Areolar  tissue  is 
subject  to  considerable  variations;  but  these  depend  rather  upon  the 
state  of  fullness  or  emptiness  of  the  vessels  which  traverse  it,  and  upon 
the  condition  of  the  walls  of  those  vessels,  than  upon  any  change  in 
the  tissue  itself.  It  has  been  shown  that,  when  an  albuminous  fluid 
is  in  contact  with  an  animal  membrane,  the  watery  part  of  the  fluid 
will  pass  through  by  transudation ;  but  that  the  albuminous  matter 
will  be  for  the  most  part  kept  back,  so  that  only  a  very  small  propor- 
tion of  it  is  to  be  found  in  the  transuded  liquid.  This  appears  to  be 
a  sufficient  explanation  of  the  presence  of  a  weak  serous  fluid  in  the 
cavities  of  areolar  tissue  ;  and  there  is  not  any  necessity,  therefore,  to 
imagine  the  existence  of  a  secreting  power,  either  in  the  areolar  tissue 
itself,  or  in  the  walls  of  the  capillaries  which  traverse  it.  When 
there  is  a  want  of  firmness  or  tone  in  the  walls  of  the  vessels,  pro- 
ducing (as  we  shall  hereafter  see,  §  609)  an  increased  pressure  of  the 
contained  fluid  on  their  walls,  and  diminished  resistance,  the  watery 
part  of  the  blood  will  have  an  unusual  tendency  to  transudation  ;  and 
we  accordingly  find  that  it  then  distends  the  areolse,  and  produces 
dropsy.  The  physical  arrangement  of  the  parts  of  the  tissue  is  so 
much  altered,  that  its  elasticity  is  impaired  ;  and  it  consequently  pits 
on  pressure, — that  is,  when  pressure  has  made  an  indentation  in  the 
surface,  this  is  not  immediately  filled  up  when  the  pressure  is  with- 
drawn, but  a  pit  remains  for  some  seconds  or  even  minutes.  The 
free  communication  which  exists  amongst  the  interstices,  is  shown  by 
the  influence  of  gravity  upon  the  seat  of  the  dropsical  effusion;  this 


SEROUS  MEMBRANES.— SKIN,  AND  MUCOUS  MEMBRANES.      129 

always  having  the  greatest  tendency  to  manifest  itself  in  the  most 
depending  parts, — a  result,  however,  which  is  also  due  to  the  in- 
creased delay,  w^hich  takes  place  in  the  circulation  in  such  parts, 
when  the  vessels  are  deficient  in  tone.  This  freedom  of  communica- 
tion is  still  more  shown,  however,  by  the  fact,  that  either  air  or  water 
may  be  made  to  pass,  by  a  moderate  continued  pressure,  into  almost 
every  part  of  the  body  containing  Areolar  tissue;  although  introduced 
at  only  a  single  point.  In  this  manner  it  is  the  habit  of  butchers  to 
inflate  veal ;  and  impostors  have  thus  blown-up  the  scalps  and  faces 
of»their  children,  in  order  to  excite  commiseration.  The  whole  body 
has  been  thus  distended  with  air  by  emphysema  in  the  lung;  the  air 
having  escaped  from  the  air-cells  into  the  surrounding  areolar  tissue, 
and  thence,  by  continuity  of  this  tissue  with  that  of  the  body  in  gene- 
ral at  the  root  or  apex  of  the  lungs,  into  the  entire  fabric. 

197.  The  structure  of  the  Serous  and  Synovial  Membranes  is 
essentially  the  same  with  that  of  Areolar  tissue.  Their  free  surface 
is  covered  with  a  layer  of  cells ;  but  these  constitute  a  distinct  tissue, 
the  Epitheliuniy  of  which  an  account  will  be  given  hereafter.  The 
epithelium  lies  upon  a  continuous  sheet  of  membrane,  of  extreme  deli- 
cacy, in  which  no  definite  structure  can  be  discovered  ;  the  nature  of 
this,  which  is  called  the  basement  or  primary-membrane,  will  be  pre- 
sently considered  (§  206).  Beneath  this  is  a  layer  of  condensed 
Areolar  tissue,  which  constitutes  the  chief  thickness  of  the  serous 
membrane,  and  confers  upon  it  its  strength  and  elasticity ;  this  gradu- 
ally passes  into  that  laxer  variety,  by  which  the  membrane  is  attached 
to  the  parts  it  lines,  and  which  is  commonly  knowm  as  the  sub-serous 
tissue.  The  yellow  fibrous  element  enters  largely  into  the  composi- 
tion of  the  membrane  itself;  and  its  filaments  interlace  in  a  beautiful 
network,  which  confers  upon  it  equal  elasticity  in  every  direction. 
The  membrane  is  traversed  by  blood-vessels,  nerves,  and  lymphatics, 
in  varying  proportions ;  some  of  the  synovial  membranes,  especially 
that  of  the  knee-joint,  are  furnished  with  little  fringe-like  projections, 
which  are  extremely  vascular,  and  which  seem  especially  concerned 
in  the  secretion  of  the  synovial  fluid.  The  fluid  of  the  serous  cavities 
is  so  nearly  the  same  as  the  serum  of  the  blood,  that  the  simple  act 
of  transudation  is  sufficient  to  account  for  its  presence  in  their  sacs;  on 
the  other  hand,  that  of  the  Synovial  capsules,  and  of  the  Bursae  Mu- 
cosae which  resemble  them,  may  be  considered  as  serum  with  from  6 
to  8  per  cent,  of  additional  albumen. 

198.  The  elements  of  Areolar  tissue  enter  largely  also  into  two 
other  textures,  which  perform  a  most  important  share  in  both  the 
Organic  and  the  Animal  functions ; — namely,  the  Mucous  Membranes 
and  the  Skin.  These  textures  are  continuous  with  each  other;  and 
may,  in  fact,  be  considered  as  one  and  the  same,  modified  in  its  dif- 
ferent parts  according  to  the  function  it  is  destined  to  perform.  Thus 
it  is  everywhere  extremely  vascular ;  but  the  supply  of  blood  in  the 
skin  is  chiefly  destined  for  the  nervous  system,  and  is  necessary  to 
the  act  of  sensation  ;  whilst  that  of  the  internal  skin  or  mucous  mem- 

9 


130  SKIN,  AND  MUCOUS  MEMBRANES. 

brane  is  rather  subservient  to  the  processes  of  absorption  and  secre- 
tion. This  tissue  is  continued  from  the  external  surface  of  the  body 
by  the  several  orifices  and  outlets  of  its  cavities ;  and  it  is  further 
continued  most  extensively  from  its  primary  internal  prolongations, 
into  the  inmost  recesses  of  the  glandular  structures. 

199.  Thus  the  gastro-intestinal  mucous  membrane  commences  at 
the  mouth,  and  lines  the  whole  alimentary  canal  from  the  mouth  to 
the  anus,  where  it  again  becomes  continuous  wath  the  skin  ;  and  it 
sends  off  as  branches,  the  membranous  linings  of  the  ducts  of  the  sali- 
vary glands,  pancreas,  and  liver ;  these  membranes  proceed  into  all 
the  subdivisions  of  the  ducts,  and  line  the  ultimate  follicles  or  ccEca 
in  which  they  terminate.  Again  the  bronchia-pulmonary  mucous 
membrane  commences  at  the  nose,  and  passes  along  the  air-passages, 
down  the  trachea,  through  the  bronchi  and  their  subdivisions,  to  line 
the  ultimate  air-cells  of  the  lungs ;  communicating  in  its  course  with 
the  gastro-intestinal.  Another  mucous  membrane  of  small  extent 
commences  at  the  puncta  lachrymalia,  lines  the  lachrymal  sac  and  the 
nasal  duct,  and  becomes  continuous  with  the  preceding.  Another, 
w^hich  may  be  considered  a  kind  of  offset  from  either  of  the  first  two, 
passes  up  from  the  pharynx  along  the  Eustachian  tube,  and  lines  the 
cavity  of  the  tympanum. 

200.  Near  the  opposite  termination  of  the  alimentary  canal,  more- 
over, we  have  the  genito-urinary  mucous  membranes ;  these  com- 
mence in  the  male  by  a  single  external  orifice,  that  of  the  urethra  ; — 
passing  backwards  along  the  urethra,  the  genital  division  is  given  off, 
to  line  the  seminal  ducts,  the  vesiculse  seminales,  the  vasa  deferentia, 
and  the  secreting  tubuli  of  the  testis  ;  another  division  proceeds  along 
the  ducts  of  the  prostate  gland,  to  line  its  ultimate  follicles,  and  an- 
other along  the  ducts  of  Cowper's  glands ;  whilst  the  miliary  division 
lines  the  bladder,  passes  up  along  the  ureters  to  the  kidney,  and  then 
becomes  continuous  with  the  membrane  of  the  tubuli  uriniferi.  In 
the  female,  the  urinary  division  commences  at  once  from  the  vulva ; 
whilst  the  genital  passes  along  the  vagina  into  the  uterus,  and  thence 
along  the  Fallopian  tubes  to  their  fimbriated  extremities,  where  it  be- 
comes continuous  with  the  serous  lining  of  the  abdominal  cavity,  the 
peritoneum. 

201.  Besides  the  glandular  prolongations  here  enumerated,  there 
are  many  others,  both  from  the  internal  and  external  surface.  Thus 
we  have  the  Mammary  mucous  membrane,  commencing  from  the 
orifices  of  the  lactiferous  ducts,  passing  inwards  to  line  their  subdi- 
visions, and  forming  the  walls  of  the  ultimate  follicles.  In  the  same 
manner  the  Lachrymal  mucous  membrane  is  prolonged  from  the  con- 
junctival mucous  membrane,  w^hich  covers  the  eye  and  lines  the  eye- 
lids, and  w^hich  is  continuous  with  the  skin  at  their  edges.  There 
are  several  minute  glands,  again,  in  the  substance  of  the  skin,  and  in 
the  walls  of  the  alimentary  canal,  which  need  not  be  here  enume- 
rated; but  which  contribute  immensely  to  the  extension  of  the  sur- 
face of  the  raucous  membrane  ;  a  prolongation  of  this  being  the  essen- 


SKIN,  AND  MUCOUS  MEMBRANES.  131 

tial  constituent  in  every  one.  In  their  simplest  form,  these  glandulae 
are  nothing  more  than  little  pits  or  depressions  of  the  surface  ;  these 
are  found  both  in  the  Skin  and  Mucous  membrane,  and  are  particularly 
destined  for  the  production  of  their  protective  secretions,  hereafter  to 
be  described. 

202.  We  have  seen,  then,  that  the  essential  character  of  the  Mu- 
cous membranes,  as  regards  their  arrangement,  is  altogether  different 
from  that  of  the  serous  and  synovial  membranes.  For  whilst  the 
latter  form  shut  sacs,  the  contents  of  which  are  destined  to  undergo 
little  change,  the  former  constitute  the  walls  of  tubes  or  cavities,  in 
which  constant  change  is  taking  place,  and  which  have  free  outward 
communications.  Thus  in  the  gastro-intestinal  mucous  membrane, 
we  have  an  inlet  for  the  reception  of  the  food  and  a  cavity  for  its 
solution,  the  walls  of  which  are  endowed  in  a  remarkable  degree  with 
absorbing  power,  whilst  they  are  also  furnished  with  numerous  glan- 
dulae,  which  pour  the  solvent  fluid  into  the  cavity.  On  the  other 
hand,  it  has  an  outlet,  through  which  the  indigestible  residuum  is 
cast  forth,  together  with  the  excretions  from  the  various  glands  that 
pour  their  products  into  the  alimentary  tube.  In  the  bronchio-pul- 
monary  apparatus,  the  same  outlet  serves  for  the  introduction  and  for 
the  expulsion  of  the  air;  and  here,  too,  is  continual  change.  In  other 
cases,  there  is  but  a  single  outlet ;  and  the  change  is  of  a  simpler  cha- 
racter, consisting  merely  in  the  expulsion  of  the  matters  eliminated 
from  the  blood  by  the  agency  of  the  glands.  Now  it  is,  as  we  shall 
see  hereafter,  in  the  digestion  and  absorption  of  food,  on  the  one 
hand,  and  in  the  rejection  of  effete  matters  on  the  other,  that  the 
commencement  and  termination  of  the  nutrient  processes  consist;  and 
these  operations  are  performed  by  the  system  of  Mucous-membranes, 
including  in  that  general  term  the  Skin,  which  is  an  important  organ 
of  excretion,  besides  serving  as  the  medium  through  which  sensory 
impressions  of  a.  general  character  are  received  by  the  Nervous  system. 

203.  The  Mucous  Membrane  may  be  said,  like  the  serous,  to  con- 
sist of  three  chief  parts ; — the  epithelium  or  epidermis  covering  its 
free  surface  ; — the  subjacent  basement-membrane  ; — and  the  areolar 
tissue,  with  its  vessels,  nerves,  &c.,  which  forms  the  thickness  of  the 
membrane,  and  connects  it  with  the  subjacent  parts.  The  Epidermis 
and  Epithelium  alike  consist  of  cells  ;  but  the  function  of  the  former 
(which  consists  of  several  layers,  of  which  the  outer  are  dry  and  horny) 
is  simply  protection  to  the  delicate  organs  beneath  ;  whilst  that  of  the 
latter  is  essentially  connected  with  the  process  of  Secretion,  as  w^ill 
be  shown  hereafter.  The  basement-membrane  resembles  that  of  the 
serous  membranes  ;  but  its  separate  existence  is  unusually  evident  in 
some  parts  where  it  exists  alone,  as  in  the  tubuli  uriniferi  of  the  kid- 
ney ;  whilst  it  can  with  difficulty  be  demonstrated  in  others,  as  the 
skin.  The  Areolar  tissue  of  Mucous  membranes  usually  makes  up 
the  grea4:est  part  of  their  thickness ;  and  it  is  so  distinct  from  that  of 
the  layers  beneath,  constituting  the  sub-mucous  tissue,  as  to  be  readily 
separable  from  them.     It  differs  not  in  any  important  particular,  how- 


132 


SKIN,  AND  MUCOUS  MEMBRANES. 


ever,  from  the  same  tissue  elsewhere  ;  and  the  white  and  fibrous 
elements  may  be  detected  in  it  in  varying  proportions,  in  different 
parts, — the  latter  being  especially  abundant  in  the  skin  and  lungs, 
which  owe  to  it  their  peculiar  elasticity.  Hence  the  Mucous  mem- 
branes yield  Gelatin  in  abundance,  on  being  boiled.  The  skin  also 
appears  to  contain  some  of  the  non-striated  Muscular  fibre  (§  337), 
in  varying  proportions  in  its  different  parts. 

204.  The  relative  amount  of  Blood-vessels,  Nerves  and  Lympha- 
tics, as  already  mentioned,  is  subject  to  great  variation,  according  to 


Fig.  8. 


Distribution  of  Capillaries  at  the 
surface  of  the  skin  of  the  finger. 


Distribution  of  Capillaries  in  the 
Villi  of  the  Intestine. 


the  part  of  the  system  examined.  The  first,  however,  are  most  con- 
stantly abundant,  being  required  in  the  Skin  for  sensation,  and  in  the 
Mucous  membranes  for  absorption  and  secretion.  In  fact  we  might 
say  of  many  of  the  mucous  membranes,  especially  those  of  the  glands, 
that  their  whole  purpose  is  to  give  support  to  the  secreting  cells,  and 
to  convey  blood-vessels  into  their  immediate  neighbourhood,  whence 
these  cells  may  obtain  materials  for  their  development.  The  Skin  is 
the   only  part  of  the  whole  system   which   is  largely  supplied  with 


Fig.  9. 


Fig.  10. 


Distribution  of  Capillaries  around 
follicles  of  Mucous  Membrane. 


Distribution  of  Capillaries  around  the 
follicles  of  Parotid  Gland. 


Nerves,  except  the  Conjunctival  membrane,  and  the  Mucous  mem- 
brane of  the  nose  ;  hence  the  sensibility  of  the  internal  mucous  mem- 
brane is  usually  low,  although  its  importance  in  the  organic  functions 
is  so  great.  The  Skin  is  copiously  supplied  with  Lymphatics  ;  and 
the  first  part  of  the  alimentary  canal  with  Lacteals ;  some  of  the 
glandular  organs  are  also  largely  supplied  with  Lymphatics. 


BASEMENT  OR  PRIMARY  MEMBRANE. 

Fig.  11. 


133 


Distribution  of  the  tactile  nerves  at  the  extremity  of  the  human  thumb,  as  seen  in  a  thin  perpendicu- 
lar section  of  the  skin, 

205.  The  Areolar  tissue,  whether  existing  separately,  or  as  forming 
a  part  of  the  Serous  and  Mucous  Membranes,  is  capable  of  being  very 
quickly  and  completely  regenerated  ;  indeed,  we  often  find  that  losses 
of  substance  in  other  tissues  are  replaced  by  means  of  it.  As  to  the 
precise  mode  of  its  production,  there  is  not  yet  a  general  agreement 
amongst  Microscopists ;  some  holding  that  its  fibres  are  produced  by  the 
transformation  of  cells  in  the  manner  hereafter  to  be  described  (§  258 
and  Fig.  33);  whilst  others  regard  it  as  originating  in  the  simple  con- 
solidation of  Fibrin  under  peculiar  circumstances.  To  the  latter  of 
these  opinions  the  Author  inclines ;  chiefly  on  account  of  the  strong 
resemblance  between  the  fibres  of  Areolar  tissue,  and  those  which 
are  unquestionably  formed  by  such  a  consolidation.  It  is  not  to  be 
denied,  however,  that  traces  of  cells  are  to  be  met  with  amongst  these 
tissues;  but  as  it  will  be  shown  that  most,  if  not  all,  fibrinous  exuda- 
tions contain  cells,  their  presence  affords  no  proof  that  the  mass  of 
fibres  have  originated  in  a  process  of  transformation  ; — the  fact  that  a 
definite  fibrous  tissue  may  have  its  origin  in  the  coagulation  of  fibrin, 
being  beyond  a  doubt. 


3.   Of  the  Basement  or  Primary  Membrane. 

206.  In  many  parts  of  the  Animal  body,  w^e  meet  with  membranous 
expansions  of  extreme  delicacy  and  transparency,  in  which  no  definite 
structure  can  be  discovered ;  and  these  seem,  like  the  simple  fibres 
already  described,  to  have  been  formed,  rather  directly  from  the  nu- 
tritive fluid,  than  indirectly  by  any  previous  process  of  transformation. 
Hence  we  may  regard  such  membranes  and  fibres  as  constituting  the 
most  simple  or  elementary  forms  of  Animal  tissue.  The  characters 
of  membranes  of  this  kind  were  first  pointed  out  by  Mr.  Bowman 
and  Mr.  J.  Goodsir ;  by  the  former  of  whom  it  was  termed  basement- 
membrane,  as  being  the  foundation  or  resting-place  for  the  epithelium- 
cells  which  cover  its  free  surface  (§  231);  w^hilst  by  the  latter  it  was 
termed  the  primary  membrane,  as  furnishing  the  germs  of  those  cells. 
These  terms  appear  equally  appropriate,  and  may  be  used  indiffer- 
ently.— In  its  very  simplest  form,  the  basement-membrane  is  a  pellicle 
of  such  extreme  delicacy,  that  its  thickness  scarcely  admits  of  being 


134  BASEMENT  OR  PRIMARY  MEMBRANE. 

measured ;  it  is,  to  all  appearance,  perfectly  homogeneous,  and  pre- 
sents not  the  slightest  trace  of  structure  under  the  highest  powers  of 
the  microscope,  appearing  like  a  thin  film  of  coagulated  gelatin. 
Examples  of  this  kind  may  be  easily  procured,  by  acting  upon  the 
inner  layer  of  any  bivalve  shell  with  dilute  acid ;  this  dissolves  away 
the  calcareous  matter  and  leaves  the  basement-membrane.  In  other 
cases,  however,  the  membrane  is  not  so  ho- 
^'s'^^-  mogeneous;    a  number  of  minute   granules 

being  scattered,  with  more  or  less  of  uni- 
formity, through  the  transparent  substance. 
And  w^e  not  unfrequently  find,  in  place  of 
these  uniformly  distributed  granules,  a  series 
of  distinct  spots,  arranged  at  equal  or  varia- 
ble distances,  and  in  different  directions,  as 
shown  in  Fig.  12.  Moreover,  the  mem- 
Portion  of  the  primary  mem-     braue  thus  coustitutcd  is  disDoscd  to  break 

brane  of  Ihe  human  intra-glaud-  .  .  _  ,      .        ^  ^        n      •>  •    \ 

ular  lymphatics,  with  its  germi-       Up  lUtO  portlOUS  Of  equal  SlZC,   Cach  01  WhlCh 

SlseToV^Jit""''^""'  ""'"'  contains  one  of  these  spots;  whilst  in  the 
more  homogeneous  forms  previously  de- 
scribed, we  find  no  such  tendency,  no  appearance  of  any  definite 
arrangement  being  perceptible  when  they  are  torn. — Hence  it  would 
seem  as  if  the  first  and  simplest  form  were  produced  by  the  simple 
consolidation  of  a  thin  layer  of  homogeneous  fluid  ;  the  second,  by  a 
layer  of  such  fluid,  including  granules;  and  the  third,  by  the  coa- 
lescence of  flattened  cells,  whose  further  development  had  been 
checked. — We  find  the  primary  membrane  under  one  or  other  of 
these  forms,  on  all  the  free  surfaces  of  the  body,  beneath  the  epithe- 
lial or  epidermic  cells.  Thus,  as  already  mentioned,  it  constitutes  the 
outer  layer  of  the  true  Skin  ;  it  lines  all  the  cavities  formed  by  Mucous 
membranes,  and  is  prolonged  into  all  the  ducts  and  ultimate  follicles 
and  tubuli  of  the  Glands  which  are  connected  with  them  (§  198);  in- 
deed it  may  be  said  in  many  instances  to  be  the  sole  constituent  of  the 
walls  of  these  follicles  and  tubuli,  the  subjacent  tissue  not  being  con- 
tinued to  their  finest  ramifications.  Again,  it  forms  the  innermost 
layer  of  the  serous  and  synovial  membranes ;  and  it  also  lines  the 
blood-vessels  and  lymphatics,  forming  the  sole  constituent  of  the 
walls  of  their  minutest  divisions. 

207.  In  every  one  of  these  cases,  we  find  ihefiee  aspect  of  the  pri- 
mary membrane  in  contact  with  cells,  which  form  a  more  or  less  con- 
tinuous layer  upon  its  surface.  These  cells  can  only  receive  their 
nutriment  by  the  imbibition  of  fluid,  through  the  primary  membrane, 
from  the  blood  brought  to  its  attached  surface  by  the  capillary  ves- 
sels of  the  tissue  with  which  it  is  in  relation.  Thus  in  the  skin  and 
mucous  membranes,  a  very  copious  supply  of  blood  is  brought  to  the 
attached  surface  of  the  primary  membrane,  by  the  minutely-distributed 
capillaries  which  form  a  large  part  of  the  subjacent  tissue  ;  and  it  is 
from  these  that  the  epidermis  and  epithelium  draw  their  nourishment, 
through  the  primary  membrane.     In  like  manner,  the  ultimate  follicles 


BASEMENT  OR  PRIMARY  MEMBRANE.  135 

and  tubuli  of  the  glands  are  surrounded  by  a  copious  network  of 
capillaries  (Fig.  10) ;  and  it  is  from  these,  through  the  primary  mem- 
brane, that  the  cells  of  these  follicles  draw  their  nourishment.  Hence 
this  membrane,  in  every  instance,  forms  a  complete  septum,  on  the  one 
hand  between  the  stream  of  blood  in  the  vessels  and  the  surround- 
ing tissues,  since  it  forms  the  lining  even  of  the  minutest  capillaries ; 
and  on  the  other  between  the  fluids  in  the  interstices  of  the  substance 
of  the  true  skin,  the  mucous  membranes,  &c.,  and  the  cells  covering 
their  free  surfaces.  It  is  evident,  therefore,  that  whilst  bounding 
th^se  tissues  and  restraining  the  too  free  passage  of  fluids  from  their 
surfaces,  it  allows  the  transudation  of  a  suflScient  amount  for  the  nu- 
trition of  the  cells  which  lie  upon  it;  and,  as  we  shall  presently  see, 
these  cells  frequently  pass  through  all  their  stages  of  growth  so  rapidly, 
that  a  very  free  supply  of  nutriment  must  be  required  by  them. 
Hence,  notwithstanding  its  apparent  homogeneousness,  the  primary 
membrane  must  have  a  structure  which  readily  admits  the  passage  of 
fluid.  In  this  respect  it  corresponds  with  the  membrane,  which  forms 
the  wall  of  the  cells  of  both  Animal  and  Vegetable  tissues  ;  for  this 
also  appears  completely  homogeneous  and  structureless,  when  seen 
under  its  simplest  aspect,  and  yet  allows  the  free  passage  of  fluids 
from  one  cell  to  another. 

208.  But  it  is  probable  that  this  membrane  performs  a  much  more 
important  office  than  that  of  simply  limiting  the  fluids,  whilst  allow- 
ing the  requisite  transudation.  We  cannot  account  for  the  new  pro- 
duction of  cells,  which  (as  will  presently  appear)  is  continually  taking 
place  on  its  surface,  without  referring  to  it  as  the  originator  of  these 
cells, — that  is,  as  the  source  of  their  germs.  The  new  generations  of 
cells  cannot  here  be  developed  by  the  reproductive  powers  of  the  old 
ones  (§211);  since  the  latter  are  often  completely  cast  off*  entire, 
before  they  can  liberate  the  reproductive  granules ;  or  they  undergo 
changes  which  evidently  unlit  them  for  such  a  purpose.  Thus  in  the 
Epidermis  we  shall  find  that  they  become  flattened  into  dry  scales, 
forming  an  almost  horny  layer  on  the*  surface  of  the  body ;  whilst  the 
new  cells  are  originating  beneath,  from  the  surface  of  the  basement- 
membrane  (§  224  and  Fig.  16).  Hence  we  cannot  find  any  other 
origin  for  these  cells  than  in  the  basement-membrane  itself;  and  there 
seems  every  probability  that  the  granules,  which  have  been  mentioned 
as  being  frequently  diffused  through  it,  are  in  reality 
the  germs  of  cells  to  be  developed  from  its  surface  ;  Fig.  is. 

whilst  the  distinct  spots  are  collections  of  similar 
granules,  each  of  which  may  give  origin  to  a  large 
number  of  such  cells,  which  spring  from  them  as 
from  a  centre.     We   shall   presently   see   that  these  _ 

''  germinal  centres"  closely  resemble  the  nuclei  of  component  ceiis 
cells  in  general,  from  which  it  is  unquestionable  that    ^^  primary   mem- 

r         n  •  /c-    ^r^  rr«i  1        i-^         brane,    with    adhe- 

new  crops  ot  cells  may  arise  (§  250).      ihe  only  dii-     rem epitUeUai ceus. 

ference  is,  that  in  the  latter  case,  the  groups  of  new 

cells  are  for  a  time  contained  within  the  parent-cell  (Fig.  30) ;  whilst 


136  SIMPLE  ISOLATED  CELLS. 

in  the  former,  they  are  developed  on  the  free  surface  of  the  base- 
ment membrane.  In  Fig.  13  is  shown  a  portion  of  the  same  mem- 
brane as  that  represented  in  Fig.  12 ;  but  having  been  rendered 
transparent  by  acetic  acid,  its  real  nature  as  a  layer  of  flattened  nu- 
cleated cells  is  more  obvious;  the  nucleus  or  germinal  spot  of  the 
central  cell  has  given  origin  to  a  cluster  of  oval  epithelial  cells,  of 
which  five  still  adhere  to  it. 

209.  Hence  w^e  are  probably  to  regard  this  primary  or  basement 
membrane  as  transitional,  rather  than  a  permanent  structure ;  and  to 
look  upon  it  as  furnishing  the  germs  of  all  the  cells,  which  are  de- 
veloped upon  its  surface;  as  well  as  the  medium,  through  which  they 
are  supplied  wdth  nutriment.  It  must  be  continually  undergoing 
disintegration,  therefore,  on  itsyree  surface;  and  must  be  as  continu- 
ally renewed,  at  the  side  in  relation  with  the  blood-vessels. 

4.   Of  Simple  Isolated  Cells,  employed  in  the  Organic  Functions. 

210.  The  active  functions  of  the  Animal  body  are  performed,  to  a 
much  greater  extent  than  was  until  lately  believed,  by  the  agency  of 
simple  isolated  cells;  of  which  every  one  grows  and  lives  quite  inde- 
pendently of  the  rest,  just  as  if  it  were  one  of  the  simplest  cellular 
plants  (§  30);  but  of  w^hich  all  are  dependent  upon  the  general  nu- 
tritive fluid  for  the  materials  of  their  development,  imbibing  it  from 
the  currents  that  circulate  in  their  neighbourhood.  It  may  be  said, 
indeed,  that  all  the  Vegetative  functions  of  the  body, — all  the  pro- 
cesses of  Nutrition  and  Reproduction, — all  those  operations,  in  short, 
which  are  common  to  Plants  and  Animals, — are  performed  in  the 
Animal  and  Vegetable  structures  by  the  very  same  means,  the  agency 
of  cells;  and  this  is  true,  not  only  of  the  healthy  actions,  but  of  vari- 
ous morbid  operations,  in  which  the  unusual  development  of  cells, 
possessing  peculiar  endowments,  performs  a  most  conspicuous  part. 
Hence  it  will  be  necessary  to  enter  somewhat  at  large  into  the  history 
of  cell-development  in  the  Anit^ial  body ;  and  the  various  modifica- 
tions under  which  this  process  may  take  place.  In  fact,  a  knowledge 
of  the  Physiology  of  Cells  may  be  regarded  as  the  foundation  of  all 
accurate  acquaintance  with  that  department  of  the  Science,  which 
relates  to  the  Nutritive  and  Reproductive  processes;  and  it  has  a  con- 
siderable bearing,  as  we  shall  see  hereafter,  upon  the  history  of  the 
purely  Animal  functions. 

211.  The  history  of  the  Animal  cell,  in  its  simplest  form,  is  pre- 
cisely that  of  the  Vegetable  cell  of  the  lowest  kind.  It  lives  for 
itself  and  by  itself;  and  is  dependent  upon  nothing  but  a  due  supply 
of  nutriment,  and  of  the  appropriate  stimuli,  for  the  continuance  of 
its  growth  and  for  the  due  performance  of  all  its  functions,  until  its 
term  of  life  is  expired.  It  originates  from  a  reproductive  granule, 
previously  formed  by  some  other  cell ;  this  granule  attracts  to  itself, 
assimilates,  and  organizes,  the  particles  of  the  nutrient  fluid  in  its 
neio-hbourhood ;   converts  some   of  them  into  the  substance  of  the 


SIMPLE  ISOLATED  CELLS.— LYMPH-CORPUSCLES.  137 

cell-wall,  whilst  it  draws  others  into  the  cavity  of  the  cell ;  in  this 
manner  the  cell  gradually  increases  in  size  ;  and  whilst  it  is  itself 
approaching  the  term  of  its  life,  it  usually  makes 
preparation  for  its  renewal,  by  the  development  Fig.  u. 

of  reproductive  granules  in  its  interior,  which  ~ 

may  become  the  germs  of  new  cells,  when  set 
free  from  the  cavity  of  the  parent.  There  is  an 
important  difference,  however,  in  the  endow- 
ments of  the  Animal  and  Vegetable  cell.  We 
have  seen  that  the  latter  can  in  general  obtain 
its  nutriment,  and  the  materials  for  its  secretion, 
by  itself  combining  the  inorganic  elements  into 
organic  compounds.  The  former,  however,  is  simple  isolated  ceiis.  con- 
totally  destitute  of  this  power  ;  it  can  produce  no  "^  reproductive  moie- 
organic  compound,  and  we  have  yet  to  learn  how 
far  its  power  of  transforming  one  compound  into  another  may  extend  ; 
and  its  chief  endowment  seems  to  be  that  of  attracting  or  drawing  to 
itself  some  of  the  various  substances,  which  are  contained  in  the 
nutritive  fluid  in  relation  wdth  it.  This  fluid,  as  we  shall  see  here- 
after, is  a  mixture  of  a  great  number  of  compounds  ;  and  different 
sets  of  cells  appear  destined  severally  to  appropriate  these,  just  as 
the  different  cells  of  a  parti-coloured  flower  have  the  power  of  draw- 
ing to  themselves  the  elements  of  their  several  colouring  matters. 
As  far  as  is  yet  known,  however,  the  composition  of  the  cell-wall 
is  everywhere  the  same ;  being  that  of  Proteine.  It  is  in  the  nature 
of  the  contents  of  the  cell,  that  (as  among  the  cells  of  Plants)  the 
greatest  diversity  exists ;  and  we  shall  find  that  the  purposes  of  the 
different  groups  of  cells,  in  the  Animal  economy,  depend  upon  the 
nature  of  the  products  they  secrete,  and  upon  the  mode  in  which 
these  products  are  given  back  after  they  have  been  subjected  to  the 
action  of  the  cells. 

212.  The  very  simplest  and  most  independent  condition  of  the 
Animal  Cell  is  probably  to  be  found  in  the  Blood,  the  Chyle,  and  the 
Lymph  ;  in  all  of  which  liquids  we  meet  with  floating  cells,  which 
are  completely  isolated  from  one  another,  and  which  are  consequently 
just  as  independent  as  the  vesicles  of  the  Red  Snow  or  other  simple 
cellular  Plants.  Indeed  in  the  nature  of  their  habitat^  we  may  com- 
pare them  with  the  Yeast- Plant;  for  as  this  will  only  vegetate  in  a 
saccharine  fluid  containing  vegetable  albumen,  so  do  we  find  that 
these  floating  cells  will  only  grow  and  multiply  in  the  albuminous 
fluids  of  animals.  In  their  general  appearance  they  very  closely  cor- 
respond with  the  figure  already  given  as  the  type  of  the  simple  cell. 
Their  diameter  is  pretty  uniform  in  the  different  fluids  of  the  body, 
and  even  in  different  animals  ;  being  for  the  most  part  about  l-3000th 
of  an  inch.  They  are  sometimes  nearly  spherical,  and  sometimes 
flattened  -,  when  they  present  the  latter  shape,  they  may  be  made  to 
swell  out  into  the  spherical  form  (see  Frontispiece^  i^igs.  4  and  5),  by 
the  action  of  water,  which  they  imbibe  according  to  the  laws  of  En- 
dosmose, — the  thinner  fluid,  water,  passing  towards  the  more  viscid 


138      COLOURLESS  CORPUSCLES  OF  BLOOD,  LYMPH,  AND  CHYLE. 


contents  of  the  cell,  and  mingling  with  them.  By  the  continuance  of 
this  kind  of  action,  the  cell  will  be  caused  to  burst.  These  cells, 
which  are  known  as  the  corpuscles  of  the  Chyle  and  Lymph,  and  as 
the  White  Corpuscles  of  the  Blood,  are  observed  to  contain  a  num- 
ber of  minute  molecules  in  their  interior  {Front.  Fig.  4);  and  at  a 
certain  stage  of  their  development, — probably  that  which  immediately 
precedes  the  maturation  and  rupture  of  the  parent-cell, — these  mole- 
cules may  be  seen,  with  a  good  Microscope,  in  active  movement 
within  the  cavity.  The  action  of  a  very  dilute  solution  of  potash 
causes  the  immediate  rupture  of  these  cells,  and  the  discharge  of  the 
contained  molecules,  which  are  probably  the  germs  of  new  cells  of  a 
similar  character.  And  when  they  rupture  spontaneously,  which 
they  are  much  disposed  to  do  under  the  influence  of  contact  with  air, 
the  fluid  which  they  set  free  shows  an  obvious  tendency  to  assume  a 
fibrous  arrangement. 

213.  There  is  reason  to  think  that  these  cells  have  for  their  office 
the  transformation  of  Albumen  into  Fibrin  ;  that  is  to  say,  the  ela- 
boration of  the  spontaneously-coagulating  and  fibrillating  substance, 
from  the  mere  chemical  compound  which  forms  the  raw  material  of 
the  Animal  tissues.  For  we  find  these  cells  in  every  situation  in 
which  we  know  the  transformation  to  be  going  on ;  and  we  observe 
their  number  to  bear  a  close  relation  with  the  amount  of  fibrin  pro- 
duced in  the  fluid.  Thus  in  the  Inflammatory  process,  the  quantity 
of  fibrin  in  the  blood  is  very  greatly  augmented ;  and  the  number  of 
white  corpuscles  found  in  that  fluid,  when  it  is  drawn  from  the  body, 
is  very  largely  increased.  Moreover  they  are  observed  to  accumulate 
in  great  numbers  in  the  vessels  of  inflamed  parts  ;  and  not  only  in 
these,  but  in  all  parts  where  processes  of  growth  and  reparation  are 
going  on,  which  require  a  large  supply  of  highly-elaborated  fibrin. 
They  are  found,  too,  in  the  exudations  of  fibrinous  matter,  poured  out 
from  the  blood  upon  wounded  or  inflamed  surfaces ;  and  here  they 
show  the  very  same  properties  as  the  w^hite  or  colourless  corpuscles 
of  the  blood, — that  is,  they  exhibit  moving  molecules  in  their  inte- 
rior ;  they  burst  and  emit  these  when  brought  in  contact  with  an  alka- 
line solution ;  and  their  fluid  contents  show  a 
disposition  to  fibrillate,  when  they  are  not  al- 
tered by  any  chemical  reagent.  Hence  it  may 
be  concluded  that  they  belong  to  the  same 
class  of  cells  ;  being  probably  developed  from 
granular  germs  set  free  from  the  blood,  along 
with  the  matter  of  the  fibrinous  exudation  itself. 
214.  The  history  of  the  simple  Animal  cell 
corresponds,  therefore,  in  all  essential  parti- 
culars with  that  which  has  been  already  de- 
scribed as  the  simplest  form  of  Life  or  Vital 
Activity ;  but  we  now  see  how  the  separate 
Colourless  cells,  with.factive  Hfc  of  the  individual  cells  is  made  to  contri- 
Sn'i^iTpesftPaiis!^  ""^  ^^''"'    butc  to  the  general  life  of  the  entire  organism, 


Fig.  15. 


COLOURLESS  AND  RED  CORPUSCLES  OF  BLOOD.       139 

and  is  at  the  same  time  dependent  upon  it.  If  the  nutrient  material 
were  not  prepared  by  other  processes,  these  cells  could  not  exist;  on 
the  other  hand,  if  this  nutrient  material  were  not  further  elaborated 
by  their  action,  no  subsequent  processes  of  growth  could  take  place. 
The  compounds  which  are  formed  as  products  of  secretion  in  the 
simple  Vegetable  cell,  are  given  back  to  the  external  world  from 
which  their  materials  were  drawn,  when  that  cell  ceases  to  exist;  to 
be  used,  perhaps,  in  the  general  economy  of  nature,  as  the  material 
for  some  other  and  higher  structure.  But  when  such  cells  themselves 
form  a  portion  of  a  higher  and  more  complex  fabric,  whether  of  the 
Plant  or  Animal,  the  substances  they  yield  back  as  the  products  of 
their  action,  are  made  use  of  in  some  other  set  of  processes  in  the 
economy  of  the  same  being.  Thus  the  fibrin-elaborating  cells,  of 
which  we  have  been  speaking,  appear  to  be  continually  growing, 
dying,  and  reproducing  themselves ;  drawing  albumen  from  the  fluid 
in  which  they  float,  and  returning  it  as  fibrin,  to  supply  the  constant 
drain  of  that  substance,  which  is  occasioned  by  the  nutritive  opera- 
tions. 

215.  Besides  the  cells  already  mentioned,  the  blood  of  Vertebrated 
animals  also  contains  others,  which  are  distinguished  by  their  red 
colour  and  flattened  form.  These  are  equally  isolated,  and  lead  an 
independent  life  ;  undergoing  all  their  changes  whilst  floating  in  the 
rapidly-circulating  current.  These  Red  Corpuscles  are  found  but 
very  sparingly  in  the  blood  of  invertebrated  animals ;  and  only  in  that 
of  the  higher  clavSses.  Their  proportion  in  the  blood  of  Vertebrata 
varies  considerably  in  the  several  groups  of  that  sub-kingdom  ;  and 
seems  to  be  closely  connected  with  the  relative  activity  of  respiration 
in  each  case.  They  present,  in  every  instance,  the  form  of  a  flattened 
disk,  which  is  circular  in  Man  and  in  most  Mammalia  {Front.  Fig.  1), 
but  which  is  oval  in  Birds,  Reptiles,  and  Fishes,  and  in  a  few  Mam- 
mals (Front.  Fig.  6).  This  disk  is  in  both  instances  a  flattened  cell, 
whose  walls  are  pellucid  and  colourless,  but  whose  contents  are  co- 
loured. Like  the  corpuscles  already  described,  they  may  be  caused 
to  swell  up  and  burst,  by  the  imbibition  of  water ;  and  the  perfect 
transparency  and  the  homogeneous  character  of  their  walls  then  be- 
come evident.  (Front.  Fig.  8,  e.)  These  red  corpuscles  are  not  only 
distinguished  from  the  others  by  the  colour  of  their  contents;  they  are 
also  characterized  by  the  absence  of  the  separate  molecules,  which 
formed  so  distinctive  a  feature  in  the  preceding;  and  in  Oviparous 
Vertebrata  by  the  presence  of  a  distinct  central  spot  or  nucleus.  This 
nucleus  appears  to  be  composed  of  an  aggregation  of  minute  granules, 
analogous  to  those  which  are  elsewhere  diffused  through  the  interior 
of  the  cell ;  and  it  is  undoubtedly  the  source  from  which  new  cells 
may  originate  within  the  parent,  as  will  be  presently  explained.  The 
nucleus  (where  it  exists)  may  be  easily  obtained  separate  from  the 
cell- wall  and  its  contents,  by  treating  the  red  corpuscles  with  water. 
The  first  effect  of  this  is  to  render  the  nucleus  rather  more  distinct,  as 
is  seen  by  contrasting  the  corpuscle  which  has  been  thus  slightly  acted 


14Q  RED  CORPUSCLES  OF  BLOOD. 

on  {Front.  Fig.  8,  «),  with  the  unaltered  corpuscle  [Front.  Fig.  6)  of 
the  same  animal.  After  a  short  time,  the  corpuscle  swells  out  and 
becomes  more  circular  {Front.  Fig.  8,  h)\  and  in  a  short  time  longer, 
the  nucleus  is  seen,  not  in  the  centre  of  the  disk,  but  near  its  margin 
(Front.  Fig.  8,  c,  d).  Finally,  the  wall  of  the  cell  ruptures ;  the  nu- 
cleus and  its  other  contents  are  set  free  ;  and  whilst  the  colouring 
matter  is  diffused  through  the  surrounding  fluid,  the  cell-walls  and 
the  nuclei  are  separately  distinguishable.  {Front.  Fig.  8,  e.) 

216.  It  is  remarkable,  however,  that  the  red  corpuscles  of  the  blood 
of  Mammals  should  possess  no  obvious  nucleus  ;  the  dark  spot  which 
is  seen  in  their  centre  {Front.  Fig.  1),  being  merely  an  effect  of  refrac- 
tion in  consequence  of  the  double-concave  form  of  the  disk.  When 
the  corpuscles  are  treated  with  water,  so  that  their  form  becomes  first 
flat,  and  then  double-convex,  the  dark  spot  disappears ;  whilst,  on 
the  other  hand,  it  is  made  more  evident  when  the  concavity  is  in- 
creased by  the  partial  emptying  of  the  cell,  which  may  be  accomplished 
by  treating  the  blood-corpuscles  with  fluids  of  greater  density  than 
their  own  contents.  Observers  are  much  divided  upon  the  question, 
whether  or  not  the  blood-disks  of  Mammals  really  contain  a  nucleus. 
There  seems  every  probability,  from  analogy,  that  a  nucleus  exists  in 
them  as  in  all  other  red  corpuscles ;  but  it  cannot  be  brought  into 
view  by  any  ordinary  method.  Dr.  G.  O.  Rees  states,  however,  that 
by  carefully  examining  the  deposit  at  the  bottom  of  water  through 
which  red  corpuscles  had  been  diffused,  he  could  distinguish  appear- 
ances that  indicated  the  existence  of  nuclei ;  although  they  escape 
observation  when  within  the  corpuscles  themselves,  on  account  of 
their  high  refractive  power.  He  describes  them  as  being  circular 
and  flattened  like  the  red  corpuscles  themselves ;  and  about  two- 
thirds  their  diameter. 

217.  The  size  of  the  Red  Corpuscles  is  not  altogether  uniform  in 
the  same  blood  ;  thus  it  varies  in  that  of  Man  from  about  the  l-4000th 
to  the  l-2800th  of  an  inch.  But  we  generally  find  that  there  is  an 
average  size,  which  is  pretty  constantly  maintained  among  the  differ- 
ent individuals  of  the  same  species ;  that  of  Man  may  6e  stated  at 
about  l-3400th  of  an  inch.  The  round  corpuscles  of  the  Mammalia 
do  not  in  general  depart  very  widely  from  this  standard ;  except  in 
the  case  of  the  Musk-Deer,  in  which  they  are  less  than  l-12000th  of 
an  inch  in  diameter.  It  is  in  the  Camel  tribe  alone  that  we  find 
oval  corpuscles  among  Mammals :  these  have  about  the  same  average 
length  as  the  round  corpuscles  of  Man,  but  little  more  than  half  the 
breadth. — In  Birds,  the  corpuscles  are  occasionally  almost  circular ; 
but  in  general  their  diameters  are  to  each  other  as  1 J  or  2  to  1.  The 
size  of  the  corpuscles  is  usually  greater  according  to  the  size  of  the 
Bird  ;  thus  among  the  Ostrich  tribe,  the  long  diameter  is  about 
l-1650th  of  an  inch,  and  the  short  diameter  l-3000th  ;  whilst  among 
the  small  Sparrows,  Finches,  &c.,  the  long  diameter  is  about  l-2400th, 
and  the  short  frequently  does  not  exceed  half  that  amount. 

218.  It  is  in  Reptiles  that  we  find  the  largest  red  corpuscles ;  and 


RED  CORPUSCLES  OF  BLOOD.  141 

it  is  in  their  blood,  therefore,  that  we  can  best  study  the  characters  of 
these  bodies.  The  blood-discs  of  the  Frog,  from  the  facility  with 
which  they  maybe  obtained,  are  particularly  suitable  for  the  purpose  ; 
their  long  diameter  is  about  the  1-lOOOth  of  an  inch,  whilst  their 
short  or  transverse  diameter  is  about  1-I800th.  The  curious  Proteus, 
Siren,  and  other  allied  species,  which  retain  their  gills  through  their 
whole  lives,  are  distinguished  by  the  enormous  size  of  their  blood- 
disks.  The  long  diameter  of  the  corpuscles  of  the  Proteus  is  about 
l-337th  of  an  inch  ;  they  are  consequently  almost  distinguishable  with 
the  unaided  eye.  The  long  diameter  of  the  corpuscles  of  the  Siren 
is  about  l-435th  of  an  inch,  and  their  short  diameter  about  l-800th  ; 
the  long  diameter  of  the  nuclei  of  these  corpuscles  is  about  1-lOOOth, 
and  the  short  diameter  about  l-2000th  of  an  inch, — so  that  the 
nuclei  are  about  three  times  as  long,  and  nearly  twice  as  broad  as 
the  entire  human  corpuscles. 

219.  There  can  be  little  doubt  that  the  Red  Corpuscles  go  through 
the  same  history  as  other  cells ;  and  there  is  evidence  that  they  are 
rapidly  regenerated,  under  favourable  circumstances,  when  a  large 
number  of  them  have  been  lost.  When  much  blood  has  been  drawn 
from  the  body,  the  proportion  of  red  corpuscles  in  the  remaining  fluid 
is  at  first  considerably  lowered  :  since  the  fluid  portion  of  the  blood  is 
replaced  almost  immediately,  whilst  these  floating  cells  require  time 
for  their  regeneration.  Their  amount  progressively  increases,  how- 
ever, until  it  has  reached  its  proper  standard,  provided  that  a  due 
supply  of  the  materials  be  afforded.  We  shall  presently  see  that  one 
of  these  materials  is  Iron  ;  and  it  is  well  known  that  iron  administered 
internally  is  an  important  aid  in  recovery  from  severe  hemorrhages,  as 
well  as  a  valuable  remedy  for  certain  constitutional  states,  in  which 
there  is  a  diminished  power  of  producing  red  corpuscles.  Thus  in 
Chlorosis,  under  the  administration  of  iron,  the  amount  of  red  cor- 
puscles in  the  blood  has  been  doubled  within  a  short  period.  Hence 
there  can  be  no  doubt  that  the  Red  Corpuscles  are  produced  from 
germs,  and  grow  like  other  cells,  under  circumstances  favourable  to 
their  development ;  and  it  is  probable  that,  in  the  healthy  state  of  the 
system,  the  constant  production,  and  the  constant  death  and  disin- 
tegration, balance  one  another.  In  some  instances  (as  in  Chlorosis) 
the  production  is  not  sufficient  to  make  up  for  the  loss  by  death ;  and 
the  total  amount  in  the  blood  undergoes  an  extraordinary  diminution, 
sometimes  even  to  less  than  a  quarter  of  their  proper  proportion.  In 
other  cases,  under  the  influence  of  excessive  nutriment  (as  in  the 
state  termed  Plethora),  the  proportion  of  Red  Corpuscles  is  increased 
beyond  the  normal  amount ;  and  in  this  condition,  the  loss  of  a  small 
quantity  of  blood  may  be  a  preservative  from  the  evils  to  which  it  is 
incident,  from  Hemorrhage  of  various  kinds. 

220.  The  precise  mode  in  which  the  Red  Corpuscles  are  usually  de- 
veloped, has  not  yet  been  positively  determined  ;  and  there  is  still  a 
degree  of  uncertainty  with  respect  to  their  parentage, — in  other  words, 
as  to  the  source  of  their  primitive  germs.    In  the  fluid  withdrawn  from 


3y<  SIMPLE  ISOLATED  CELLS.— BLOOD-CORPUSCLES. 

the  heart  of  the  embryo  chick  about  the  third  day,  the  whole  process 
of  the  formation  of  the  oval  red  corpuscles  from  minute  granules  has 
been  distinctly  traced  ;  and  there  is  every  probability  that  these  gra- 
nules are  cell-germs  set  free  by  some  of  the  cells  of  the  primary  embry- 
onic structures,  which  thus  originate  blood-corpuscles,  in  the  same 
manner  as  other  cells  originate  bone,  nerve,  muscle,  &c.  The  subse- 
quent increase  and  constant  maintenance  of  the  number  of  red  corpus- 
cles, can  scarcely  be  due  to  any  other  process,  than  that  by  which  simi- 
lar isolated  cells  are  regenerated;  that  is,  by  the  continual  production 
of  new  generations  by  germs  prepared  by  the  parent.  According  to 
the  celebrated  Leeuwenhoek,  certain  red  corpuscles  are  occasionally 
seen  to  divide  themselves  into  six,  which,  at  first  very  small,  gradu- 
ally increase  to  the  size  of  their  parents ;  and  this  observation  has 
been  confirmed  by  Dr.  Barry,  w^ho  regards  the  multiplication  as  due 
to  the  development  of  six  young  cells,  which  sprout  from  the  circum- 
ference of  the  nucleus,  and  grow  at  first  within  the  cell-wall  of  the 
parent,  but  afterwards  rupture  it,  and  become  free.  On  the  other 
hand,  Dr.  G.  O.  Rees  affirms,  that,  when  examining  a  portion  of 
blood  maintained  at  about  its  natural  temperature,  he  observed  some 
of  the  corpuscles  to  assume  an  hour-glass  form,  by  a  contraction 
across  their  middle ;  and  that,  by  the  increase  of  this  contraction, 
producing  the  division  of  the  corpuscles,  two  unequal-sized  circular 
bodies  were  eventually  produced  from  each ;  which,  when  treated 
with  a  strong  saline  solution,  were  emptied  of  their  contents,  like 
ordinary  blood-disks.  It  can  scarcely  be  doubted  that,  in  one  of 
these  modes,  the  Red  corpuscles  reproduce  themselves;  and  that  in  this 
manner  a  continual  succession  is  kept  up.  Some  have  supposed  that 
the  Red  corpuscles  originated  from  the  White  or  colourless  corpuscles 
previously  described  ;  but  this  idea  seems  to  have  little  other  foun- 
dation, than  the  correspondence  in  size  between  the  colourless  cor- 
puscles of  the  Frog's  blood,  and  the  nuclei  of  its  red  corpuscles. 
This  correspondence  is  quite  accidental,  however;  for  in  Man,  the 
colourless  corpuscles  are  somewhat  larger  than  the  entire  red  disks ; 
in  the  Musk-deer,  they  are  far  larger;  and  in  the  Proteus  they  are  far 
smaller  than  the  nuclei  of  the  latter.  For  the  diameter  of  the  Colour- 
less corpuscle  varies  extremely  little  ;  whilst  that  of  the  red,  as  we 
have  seen,  has  a  range  from  1-337 th  of  an  inch  to  less  than 
l-12,000th. 

221.  The  Chemical  composition  of  the  walls  and  nuclei  of  the  Red 
corpuscles  is  very  different  from  that  of  their  contents.  The  substance 
of  the  former  has  been  termed  Glohuline ;  but  it  does  not  seem  to 
differ  in  any  essential  character  from  other  substances  resulting  from 
the  organization  of  the  proteine-compounds.  The  compound  which 
forms  the  contents  of  the  red  corpuscles,  however,  and  gives  them 
their  characteristic  hue,  is  altogether  peculiar,  and  has  received  the 
name  of  Hcematine.  Its  composition  is  notably  different  from  that  of 
the  proteine-compounds  ;  the  proportion  of  Carbon  to  the  other  ingre- 
dients being  very  much  greater;  and  a  definite  quantity  of  iron  being 


\ 


SIMPLE  ISOLATED  CELLS.— BLOOD-CORPUSCLES.  143 

an  essential  part  of  it.  Its  formula  is  44  Carbon,  22  Hydrogen,  3 
Nitrogen,  6  Oxygen,  and  1  Iron.  When  completely  separated  from 
albuminous  matter,  it  is  a  dark  brown  substance,  incapable  of  coagu- 
lation, nearly  insoluble  in  water,  alcohol,  ether,  acids,  or  alkalies, 
alone  ;  but  readily  soluble  in  alcohol  mixed  either  w^ith  sulphuric  acid 
or  ammonia.  The  solution,  even  when  diluted,  has  a  dark  colour; 
and  possesses  all  the  properties  of  the  colouring  matter  of  venous 
blood.  The  iron  may  be  separated  from  the  hasmatine  by  strong  re- 
agents which  combine  with  the  former,  and  the  latter  still  possesses 
its  characteristic  colour.  This  hue  cannot  be  dependent,  therefore, 
on  the  presence  of  iron  in  the  state  of  peroxide ;  as  some  have  sup- 
posed. On  the  other  hand,  the  iron  is  most  certainly  united  firmly 
with  the  ingredients  of  the  hsematine,  as  contained  in  the  red  corpus- 
cles; for  this  may  be  digested  in  dilute  sulphuric  or  muriatic  acid  for 
many  days,  without  the  least  diminution  in  the  quantity  of  iron,  the 
usual  amount  of  which  may  be  afterwards  obtained  by  combustion 
from  the  hsematine  that  has  been  subjected  to  this  treatment.  This 
experiment  seems  further  to  prove,  that  the  iron  cannot  be  united 
with  the  hsematine  in  the  state  of  either  protoxide  or  peroxide,  as 
maintained  by  Liebig;  since  weak  acids  would  then  dissolve  it  out. 

222.  Regarding  the  nature  of  this  compound,  and  the  changes  w^hich 
it  undergoes  in  respiration,  there  is  still  much  to  be  learned ;  and 
until  these  points  have  been  more  fully  elucidated,  the  precise  uses  of 
the  red  corpuscles  in  the  animal  economy  cannot  be  understood. 
There  is  evidence,  however,  that  the  production  of  Hsematine  is  (like 
the  production  of  the  red  colouring  matter  of  the  Protococcus  nivalis, 
§  31),  a  result  of  chemical  action  taking  place  in  the  cells  them- 
selves; for  no  substance  resembling  Hsematine  can  be  found  in  the 
liquid  in  which  these  cells  float,  and  scarcely  a  trace  of  iron  can  be 
detected  in  it;  whilst,  on  the  other  hand,  the  fluid  portion  of  the 
chyle  holds  a  large  quantity  of  iron  in  solution,  which  seems  to  be 
drawn  into  the  red  corpuscles,  and  united  with  the  other  constituents 
of  hsematine,  as  soon  as  ever  it  is  delivered  into  the  circulating  cur- 
rent. The  colouring  matter  appears  to  exist  in  two  states,  the  pre- 
cise chemical  difference  between  which  has  not  yet  been  ascertained. 
In  arterial  blood  it  is  a  florid  scarlet;  w^hilst  in  venous  blood  it  is  of 
a  purpler  hue.  By  circulating  through  the  capillaries  of  the  system, 
the  arterial  or  bright  hsematine  becomes  converted  into  dark  or  ve- 
nous hsematine  ;  and  the  converse  change  takes  place  in  the  capillaries 
of  the  lungs,  the  original  florid  hue  being  recovered.  Now  it  is  cer- 
tain that  the  blood,  in  its  change  from  the  arterial  to  the  venous  con- 
dition, loses  oxygen,  and  becomes  charged  with  an  increased  amount 
of  carbonic  acid,  although  its  precise  mode  of  combination  is  not 
known ;  on  the  other  hand,  in  its  return  from  the  venous  to  the  arte- 
rial state,  the  blood  gives  off"  this  additional  charge  of  carbonic  acid, 
and  imbibes  oxygen.  The  change  of  colour,  under  similar  con- 
ditions, takes  place  out  of  the  body,  as  well  as  in  it.  Thus  if 
venous  blood  be  exposed  for  a  short  time  to  the  air,  its  surface 


144  SIMPLE  ISOLATED  CELLS.— BLOOD-CORPUSCLES. 

becomes  florid  ;  and  the  non-extension  of  this  change  to  the  interior  of 
the  mass  is  evidently  due  to  the  impossibility  of  bringing  air  into  rela- 
tion with  every  particle  of  the  blood,  in  the  manner  in  which  the  lungs 
are  so  admirably  contrived  to  effect.  If  venous  blood  be  exposed  to 
pure  oxygen,  the  change  of  colour  will  take  place  still  more  speedily; 
and  it  is  not  prevented  by  the  interposition  of  a  thick  animal  mem- 
brane, such  as  a  bladder,  between  the  blood  and  the  gas.  On  the 
other  hand,  if  arterial  blood  be  exposed  to  carbonic  acid,  it  loses  its 
brilliant  hue,  and  is  rendered  as  dark  as  venous  blood;  or  even  darker, 
if  exposed  very  completely  to  its  influence.  The  simple  removal  of 
this  carbonic  acid  is  not  sufficient  to  restore  the  original  colour  ;  for 
this  removal  may  be  effected  by  hydrogen,  which  has  the  power  of  dis- 
solving out  (so  to  speak)  the  carbonic  acid  diffused  through  the  blood, 
without  the  restoration  of  the  arterial  hue,  unless  oxygen  be  present, 
or  saline  matter  be  added  to  the  blood. 

223.  These  changes  in  the  condition  of  the  contents  of  the  Red 
corpuscles,  taken  in  connection  with  the  fact,  that  these  bodies  are 
almost  completely  restricted  to  the  blood  of  Vertebrata,  (whose  respi- 
ration is  much  more  energetic  than  that  of  any  Invertebrated  animals 
save  Insects,  which  have  a  special  provision  of  a  different  character,) 
and  that  their  proportion  to  the  whole  mass  of  the  blood  corresponds 
with  the  activity  of  the  respiratory  function, — leave  little  doubt  that 
they  are  actively  (but  not  exclusively)  concerned  as  carriers  of  Oxygen 
from  the  lungs  to  the  tissues,  and  of  Carbonic  acid  from  the  tissues  to 
the  lungs  ;  and  that  they  have  no  other  direct  concern  in  the  functions 
of  Nutrition,  than  the  fulfilment  of  this  duty.  Their  complete  absence 
in  the  lower  Invertebrated  animals,  in  the  earliest  condition  of  the 
higher,  and  in  newly-forming  parts  until  these  are  penetrated  by  blood- 
vessels, seems  to  indicate  that  they  have  no  immediate  connection 
with  even  the  most  energetic  operations  of  growth  and  development ; 
whilst,  on  the  other  hand,  there  is  abundant  evidence,  that  the  normal 
activity  of  the  animal  functions  is  mainly  dependent  upon  their  pre- 
sence in  the  blood  in  due  proportion. 

224.  Next  in  independence  to  the  cells  or  corpuscles  floating  in  the 
animal  fluids,  are  those  which  cover  the  free  membranous  surfaces  of 
the  body,  and  form  the  Epidermis  and  Epithelium.  Between  these 
two  structures  there  is  no  more  real  difference,  than  there  is  between 
the  Skin  and  the  Mucous  membranes.  The  one  is  continuous  with 
the  other;  they  are  both  formed  of  the  same  elements;  they  are  cast 
off  and  renewed  in  the  same  manner ;  the  history  of  the  life  of  the 
individual  cells  of  each  is  nearly  identical ;  but  there  is  an  important 
difference  in  the  purposes,  which  they  respectively  serve  in  the  gene- 
ral economy.  The  Epidermis  or  Cuticle  covers  the  exterior  surfaces 
of  the  body,  as  a  thin  semi-transparent  pellicle,  which  is  apparently 
homogeneous  in  its  texture,  is  not  traversed  by  vessels  or  nerves,  and 
was  formerly  supposed  to  be  an  inorganic  exudation  from  the  surface 
of  the  true  Skin,  designed  for  its  protection.  It  is  now  known,  how- 
ever, to  consist  of  a  series  of  layers  of  cells,  which  are  continually 


SIMPLE  ISOLATED  CELLS.— EPIDERMIS.  145 

wearing  off  at  the  external  surface,  and  are  being  renewed  at  the 
surface  of  the  true  skin  ;  so  that  the  newest  and  deepest  layers  gradu- 
ally become  the  oldest  and  most  superficial,  and  are  at  last  thrown  off 
by  slow  desquamation.  Occasionally  this  desquamation  of  the  cuticle 
is  much  more  rapid ;  as  after  Scarlatina  and  other  inflammatory  affec- 
tions of  the  Skin. 

225.  In  their  progress  from  the  internal  to  the  external  surface  of 
the  Epidermis,  the  cells  undergo  a  series  of  well-marked  changes. 
When  we  examine  the  innermost  layer,  we  find  it  soft  and  granular; 
consisting  of  nuclei,  in  various  stages  of  development  into  cells,  held 
together  by  a  tenacious  semi-fluid  substance.  This  was  formerly 
considered  as  a  distinct  tissue,  and  was  supposed  to  be  the  peculiar 
seat  of  the  colour  of  the  skin ;  it  received  the  designation  of  rete 
mucosum.  Passing  outwards,  we  find  the  cells  more  completely 
formed ;  at  first  nearly  spherical  in  shape ;  but  becoming  polygonal 
where  they  are  flattened  against  one  another.  As  we  proceed  further 
towards  the  surface,  we  perceive  that  the  cells  are  gradually  more 
and  more  flattened,  until  they  become  mere 

horny  scales,  their  cavity  being  obliterated  ;  ^'o  i^- 

their   origin    is   indicated,    howcA^er,    by  the  ^t--   -          -^~^^ 

nucleus  in  the  centre  of  each.     This  flattening  - 
appears  to  result  from  the  gradual  desiccation 

or  drying-up  of  the  contents  of  the  cells,  which  '  J^ 

results  from  their  exposure  to  the  air.     Thus  ^                ,^ 

each  cell  of  the  Epidermis  is  developed  from  ^S^^^^^m 

the   nucleus  on  the  surface  of  the   basement  '^^\<^s~*^ 

membrane,   (which  nucleus  is  probably  fur-  '^  ^       ^9^ 

nished  by  the  membrane  itself,  §  208,)  and  is  ^  c^'S    Cr^ 

gradually  brought  to  the  surface  by  the  deve-  ^(SM^^ml. 

lopment  of  new  cells  beneath,  and  the  removal  ~^^^^fe^^^/^ 

of  the  superficial  layers  ;  whilst  at  the  same  ^,  ^^'^'^'^^^~^~^, 

.      .    *  •       1         1  ^    •       r  •!  Oblique   section  of  Epider- 

tirae  it  is  progressively  changed  in  lorm,  until  mis,  showing  uie  progressive 

it  is  converted   into  a  flattened   scale.     The  cdi^firnuciL'resSnlTpTu 

accompanying   representation    of  an    oblique  iJiLrnSef  L^rr^ee'/rbe' 

section  of  the  Epidermis,  exhibits  the  principal  gradually  developed  into  ceiis, 

,      .  r'  1  at 0.  c,  and  a,- and  the  ceils  are 

gradations  OI  its  component  structures.  flattened  into  lamellae.  forming 

226.  The  Epidermis  covers  the  whole  ex-  ^^--^eno;^  portion  of  the  ep. 
terior  surface  of  the  body  ;  not. excepting  the 

Conjunctiva  of  the  eye,  on  which,  however,  it  has  more  the  character 
of  an  Epithelium ;  and  the  Cornea,  on  which  it  participates  in  the 
horny  character  of  the  Epidermic  covering  of  the  skin.  The  con- 
tinuity is  well  seen  in  the  cast  skin  or  slough  of  the  Snake ;  in  which 
the  covering  of  the  front  of  the  eye  is  found  to  be  as  perfectly  exu- 
viated, as  that  of  any  part  of  the  body.  The  number  of  layers  varies 
greatly  in  different  parts;  being  usually  found  to  be  the  greatest, 
where  there  is  most  pressure  or  friction.  Thus  on  the  soles  of  the 
feet,  particularly  at  the  heel  and  the  ball  of  the  great  toe,  the  Epi- 
dermis is  extremely  thick ;  and  the  palms  of  the  hands  of  the  labouring 
10 


146 


SIMPLE  ISOLATED  CELLS.— EPIDERMIS. 


Horny  Epidermis,  from  conjunctiva  covering 
the  cornea;  a,  single  scales;  b,  simple  lamina 
of  epithelium;  below  is  seen  a  double  layer  of 
the  same. 


raan  are  distinguished  by  the  increased  density  of  their  horny  cover- 
ing. It  would  seem  as  if  the  irritation  of  the  Skin  stimulated  it  to  an 
increased  production  of  this  substance.     The  Epidermic  membrane 

is  pierced  by  the  excretory  ducts 
^'^•^^-  of  the  sweat  glands,  and  of  the 

sebaceous  follicles,  which  lie  in  the 
true  skin  and  immediately  beneath 
it ;  or  we  should  rather  say  that  it 
is  continuous  with  the  delicate  epi- 
thelial lining  of  these. — The  JYails 
may  be  considered  as  nothing  more 
than  an  altered  form  of  Epidermis. 
When  examined  near  their  origin, 
they  are  found  to  consist  of  cells 
which  gradually  dry  into  scales; 
and  these  remain  coherent  together. 
A  new  production  is  continually 
taking  place  in  the  groove  of  the 
skin,  in  which  the  root  of  the  nail 
is  imbedded ;  and  probably  also  from  the  whole  subjacent  surface. 

227.  The  Epidermis,  when  analyzed,  is  found  to  differ  from  the 
proteine-compounds  in  its  composition ;  but  not  in  any  very  striking 
degree.  The  proportion  of  its  elements  is  considered  to  be  48  Carbon, 
39  Hydrogen,  7  Nitrogen,  17  Oxygen ;  and  this  corresponds  exactly 
with  the  composition  of  the  substance  of  which  Nails,  Horn,  Hair  and 
"Wool  are  constituted.  It  seems  probable,  however,  that  the  cell-walls 
are  formed,  as  elsewhere,  of  Fibrin;  and  that  the  horny  matter  is  a 
secretion  in  their  interior,  which  is  drawn  from  the  elements  of  blood 
during  their  growth  and  development. 

228.  The  Epidermis  appears  solely  destined  for  the  protection  of 
the  true  Skin ;  both  from  the  mechanical  injury  and  the  pain,  which 
the  slightest  abrasion  would  produce ;  and  from  the  irritating  effects 
of  exposure  to  the  external  air,  and  of  changes  of  temperature.  We 
perceive  the  value  of  this  protection,  when  the  Epidermis  has  been 
accidentally  removed.  It  is  very  speedily  replaced,  how^ever  ;  the 
increased  determination  of  blood  to  the  Skin,  which  is  the  conse- 
quence of  the  irritation,  being  favourable  to  the  rapid  production  of 
Epidermic  cells  on  its  surface. 

229.  Mingled  with  the  Epidermic  cells,  we  find  others  which  se- 
crete colouring  matter  instead  of  horn  ;  these  are  termed  Pigment- cells. 
They  are  not  readily  distinguishable  in  the  epidermis  of  the  White 
races,  except  in  certain  parts,  such  as  the  areola  around  the  nipple, 
and  in  freckles,  nsevi,  &c.  But  they  are  very  obvious,  on  account  of 
their  dark  hue,  in  the  newer  layers  of  the  Epidermis  of  the  Negro 
and  other  coloured  races ;  and,  like  the  true  Epidermic  cells,  they 
dry  up  and  become  flattened  scales  in  their  passage  towards  the  sur- 
face, thus  constantly  remaining  dispersed  through  the  Epidermis,  and 
giving  it  a  dark  tint  Avhen  it  is  separated  and  held  up  to  the  light. 


SIMPLE  ISOLATED  CELLS.— PIGMENT  CELLS. 


147 


In  all  races  of  men,  however,  we  find  the  most  remarkable  develop- 
ment of  Pigment-cells  on  the  inner  surface  of  the  Choroid  coat  of  the 
eye,    where    they   form    several 
layers,  known  as  the  Pigmentum  Fig.  is. 

nigrum.     Here  they  have  a  very 
regular  arrangement,  which  is  best 
seen  where  they  cover  the  blood- 
vessels of  the  Choroid  coat  in  a 
single  layer,  as  shown  in  Fig.  18. 
When  examined  separately,  they 
are  found   to  have  a  polygonal 
form  (Fig.  19,  a),  and  to  have  a 
distinct  nucleus  (6)  in  their  inte- 
rior.    The  black  colour  is  given 
by  the  accumulation,  within  the 
cell,  of  a  number  of  flat,  rounded 
or  oval  granules,  measuring  about 
l-20,000th  of  an  inch  in  diameter, 
and  a  quarter  as  much  in  thick- 
ness ;     these,    when     separately 
viewed,  are  observed  to  be  trans- 
parent, not  black  and  opaque ;  and  they  exhibit  an  active  movement 
when  set  free  from  the  cell,  and  even  whilst  enclosed  within  it.    The 
pigment-cells  are   not  always  of  a  simple  rounded  or 
polygonal  form;  they  sometimes  present  remarkable  stel- 
late prolongations,  under  which  form  they  are  well  seen 
in  the  skin  of  the  Frog. — The  Chemical  nature  of  the 
black  pigment  has  not  yet  been  made  evident;  it  has 
been  shown,  however,  to  have  a  close  relation  with  that 
of  the  Cuttle-fish  ink  or  Sepia,  which  derives  its  colour 
from  the  pigment-cells  lining  the  ink-bag ;  and  to  include 
a  larger  proportion  of  Carbon  than  most  other  organic 
substances, — every   100   parts   containing   581  of  this 
element. 

230.  That  the  development  of  the  Pigment-cells,  or  at  least  the 
formation  of  their  peculiar  secretion,  is  in  some  degree  due  to  the 
influence  of  Light,  seems  evident  from  the  facts  already  mentioned 
(§  93).  To  these  it  may  be  added,  that  the  new-born  infants  of  the 
Negro  and  other  dark  races  do  not  exhibit  nearly  the  same  depth  of 
colour  in  their  skins,  as  that  which  they  present  after  the  lapse  of  a 
few  days ;  which  seems  to  indicate  that  exposure  to  light  is  necessary 
for  the  full  development  of  the  characteristic  hue.  An  occasional 
development  of  dark  pigment-cells  takes  place  during  pregnancy  in 
some  females  of  the  fair  races ;  thus  it  is  very  common  to  meet  with 
an  extremely  dark  and  broad  areola  round  the  nipple  of  pregnant 
women  ;  and  sometimes  large  patches  of  the  cutaneous  surface,  on  the 
lower  part  of  the  body  especially,  become  almost  as  dark  as  the  skin 
of  the  Negro.     On  the  other  hand,  individuals  are  occasionally  se^n 


A  portion  of  the  choroid  coat  from  the  eye  of  the 
Ox,  showing  the  pigment-cells,  where  they  cover 
a,  a,  a,  the  veins,  in  a  single  layer;  &,  b,  ramifi- 
cations of  the  veins  near  the  ciliary  ligament, 
covered  with  less  regular  pigment-cells ;  c,  c, 
spaces  between  the  vessels,  more  thickly  covered 
with  pigment-cells. 


Fig.  19. 


% 


Caopuscles  of 
Pigment,  magni- 
fied 300  diame- 
ters;—a,  cell;  b, 
nucleus. 


%4B  SIMPLE  ISOLATED  CELLS.— EPITHELIUM. 

with  an  entire  deficiency  of  pigment-cells,  or  at  least  of  their  proper 
secretion,  not  merely  in  the  skin,  but  in  the  eye  ;  such  are  termed 
Albinoes ;  and  they  are  met  with  as  well  among  the  fair,  as  among 
the  dark  races.  The  absence  of  colour  usually  shows  itself  also  in 
the  hair,  which  is  almost  white. 

231.  The  Epithelium  may  be  designated  as  a  delicate  cuticle, 
covering  the  free  internal  surfaces  of  the  body ;  and  apparently  de- 
signed, in  some  instances,  simply  for  their  protection;  whilst  in  other 
cases,  as  we  shall  presently  find,  it  serves  purposes  of  far  greater 
importance.  It  has  long  been  known  that  the  Epidermis  might  be 
traced  continuously  from  the  lips  to  the  mucous  membrane  of  the 
xnouth,  and  thence  down  the  (Esophagus  into  the  stomach;  and  that 
in  the  strong  muscular  stomach  or  gizzard  of  the  granivorous  birds, 
it  becomes  quite  a  firm  horny  lining.  But  it  has  been  only  ascer- 
tained by  the  use  of  the  Microscope,  that  a  continuous  layer  of  cells 
may  be  traced,  not  merely  along  the  whole  surface  of  the  mucous 
membrane  lining  the  alimentary  canal,  but  likewise  along  the  free 
surfaces  of  all  other  Mucous  membranes,  with  their  prolongations  into 
follicles  and  glands ;  as  well  as  on  Serous  and  Synovial  membranes, 
and  the  lining  membrane  of  the  heart,  blood-vessels,  and  absorbents. 
The  Epithelial  cells,  being  always  in  contact  with  fluids,  do  not  dry 
up  into  scales  like  those  of  the  Epidermis;  and  they  differ  from  them 
also  in  regard  to  the  nature  of  the  matter,  which  they  secrete  in  their 
interior.  In  this  respect,  however,  the  Epithelial  cells  of  different 
parts  are  unlike  one  another;  fully  as  much  as  any  of  them  are  unlike 
the  cells  of  the  Epidermis ;  for  we  shall  find  that  all  the  secretions  of 
the  body  are  the  product  of  the  elaboration  of  Epithelium  cells  ;  and 
consequently  there  are  as  many  varieties  of  endowment,  in  these  im- 
portant bodies,  as  there  are  varieties  in  the  result  of  their  action. 

232.  The  Epithelium  covering  the  Serous  and  Synovial  mem- 
branes, and  the  lining  of  the  blood-vessels,  is  composed  of  flattened 
polygonal  cells,  (resembling  those  shown  in  Fig.  20,)  lying  in  appo- 
sition with  each  other,  so  as  to  form  a  kind  of  pavement ;  hence  this 
form  is  termed  pavement  or  tesselated-Epithelmm.  There  is  no  reason 
to  believe  that  it  possesses  any  active  endowments  in  these  situations; 
since  it  does  not  appear  to  be  concerned  in  the  elaboration  of  any 
peculiar  secretion.  It  has  been  already  pointed  out  (§  196),  that  the 
fluid  of  serous  membranes  is  separated  from  the  blood  by  a  simple  act 
of  mechanical  transudation,  (which  often  takes  place  to  a  great  extent 
after  death ;)  the  walls  of  the  blood-vessels  do  not  appear  to  be  con- 
cerned in  forming  any  peculiar  secretion;  and  the  only  product  of  this 
kind,  which  indicates  any  special  endowment  in  the  epithelium-cells, 
is  the  synovia,  which  is  probably  elaborated  by  the  cells  covering 
the  vascular  fringes  of  the  synovial  membrane,  formerly  mentioned 
(§  197).  The  cells  draw  it  from  the  blood,  during  the  progress  of 
their  growth,  form  it  as  a  secretion  within  themselves,  and  then  cast 
it  into  the  general  cavity  of  the  joint,  (when  their  term  of  individual 
life  is  ended,)  either  by  the  rupture  or  the  liquefaction  of  their  walls. 


SIMPLE  ISOLATED  CELLS.— EPITHELIUM. 


149 


In  other  cases,  it  would  seem  as  if  the  epithelial  cells  were  not  fre- 
quently cast  otf  and  renewed,  but  possessed  a  considerable  perma- 
nency. It  is  to  be  remembered  that,  in  the  healthy  state  of  the  serous 
and  synovial  membranes,  and  in  that  of  the  lining  membrane  of  the 
blood-vessels  and  absorbents,  they  are  entirely  secluded  from  sources 
of  irritation ;  and  that  they  lead  a  sort  of  passive  life,  very  different 
from  the  active  life  of  the  mucous  membranes.  In  fact,  it  would 
appear  to  be  the  sole  object  of  the  serous  membranes,  to  enclose  and 
suspend  the  viscera,  in  such  a  manner  as  to  allow  of  the  access  of 
blood-vessels,  nerves,  gland-ducts,  &c. ;  and  at  the  same  time  to 
permit  them  the  required  freedom  of  motion,  and  to  provide  against 
the  irritation  of  opposing  parts,  by  furnishing  an  extremely  smooth 
and  moistened  surface,  wherever  friction  takes  place.  Hence  we 
find  membranes,  with  all  the  characters  of  serous  surfaces,  in  the 
false  joints  formed  by  ununited  fractures,  and  in  other  similar 
situations. 

233.  The  Epithelium  of  the  Mucous  membranes  and  their  pro- 
longations is  found  under  two  principal  forms,  the  tesselated,  and  the 
cylindrical.     An  example  of  the  Tesselated  form  is  shown  in  Fig.  20, 

Fiar.  21. 


Separated  Epithelium-cells,  a,  with 
miclei,  b.  and  nucleoli,  c,  from  mucous 
membrane  of  mouth. 


Pavement-Epithelium  of  the 
Mucous  Membrane  of  the  small- 
er bronchial  tubes;  a,  nuclei  with 
double  nucleoli. 


which  shows  the  separate  epithelium-cells  of  the  mucous  membrane 
of  the  mouth,  as  they  are  frequently  met  with  in  saliva.  The  cells 
are  not  always  so  polygonal  in  form,  however ;  sometimes  retaining 
their  rounded  or  oval  form,  and  being  separated  by  considerable 
interstices,  so  that  they  can  scarcely  be  said  to  form  a  continuous 
layer.  A  specimen  of  this  kind  is  seen  in  Fig.  21,  which  represents 
a  group  of  epithelium-cells  from  one  of  the  smaller  bronchial  tubes. 
This  form  of  tesselated  epithelium  is  more  commonly  met  with,  where 
the  secreting  operations  are  more  active,  the  life  of  the  cells  conse- 
quently shorter,  and  the  renewal  of  them  more  frequent ;  so  that  they 
have  not  time,  so  to  speak,  to  be  developed  into  a  more  continuous 
layer. — The  Cylinder-Epithelium  is  very  differently  constituted.  Its 
component  cell  are  cylinders,  which  are  arranged  side  by  side ;  one 
extremity  of  each  cylinder  resting  upon  the  basement-membrane, 
whilst  the  other  forms  part  of  the  free  surface.  The  perfect  cylin- 
drical form  is  only  shown,  when  the  surface  on  which  the  cylinders 
rest  is  flat  or  nearly  so.     When  it  is  convex,  the  lower  ends  or  base- 


150 


SIMPLE  ISOLATED  CELLS.— EPITHELIUM. 


Fig.  22. 


// 


ments  of  the  cells  are  of  much  smaller  diameter  than  the  upper  or 
free  extremities ;  and  thus  each  has  the  form  of  a  truncated  cone, 
rather  than  of  a  cylinder.  (Fig.  22.)  This  is  well  seen  in  the  cells 
which  cover  the  villi  of  the  intestinal  canal.  (Fig.  28.)  On  the  other 
hand,  where  the  cylinder-epithelium  lies  upon  a  concave  surface,  the 
free  extremities  of  the  cells  may  be  smaller  than  those  which  are 
attached.  Sometimes  each  cylinder  is  formed  from  more  than  one 
cell,  as  is  shown  by  the  nuclei  it  contains ;  although  its  cavity  seems 
to  be  continuous  from  end  to  end.  And  occasionally  the  cylinders 
arise  by  stalk-like  prolongations,  from  a  tesselated  epithelium  beneath. 
The  two  forms  of  Epithelium  pass  into  one  another  at  various  points; 
and  various  transitional  forms  are  then  seen, — the  tesselated  scales 
appearing  to  rise  more  and  more  from  the  surface,  until  they  project 
as  long-stalked  cells,  truncated  cones,  or  cylinders. 

234.  Both  these  principal  forms  of  Epithelial  cells  are  frequently 
observed  to  be  fringed  at  their  free  margins  with  delicate  filaments, 

which  are  termed  cilia;  and  these, 
although  of  extreme  minuteness,  are 
organs  of  great  importance  in  the  ani- 
mal economy,  through  the  extraordi- 
nary motor  powers  with  which  they 
are  endowed.  The  form  of  the  ciliary 
filaments  is  usually  a  little  flattened, 
and  tapering  gradually  from  the  base 
to  the  point.  Their  size  is  extremely 
variable ;  the  largest  that  have  been 
observed  being  about  l-500th  of  an  inch  in  length,  and  the  smallest 
about  l-13,000th.  When  in  motion,  each  filament  appears  to  bend 
from  its  root  to  its  point,  returning  again  to  its  original  state,  like  the 
stalks  of  corn  when  depressed  by  the  wind  ;  and  when  a  number  are 
affected  in  succession  with  this  motion,  the  appearance  of  progressive 
waves  following  one  another  is  produced,  as  when  a  corn-field  is 
agitated  by  frequent  gusts.  When  the  ciliary  motion  is  taking  place 
in  full  activity,  however,  nothing  whatever  can  be  distinguished,  but 
the  whirl  of  particles  in  the  surrounding  fluid  ;  and  it  is  only  when 
the  rate  of  movement  slackens,  that  the  shape  and  size  of  the  cilia, 
and  the  manner  in  which  their  stroke  is  made,  can  be  clearly  seen. 
The  motion  of  the  cilia  is  not  only  quite  independent  (in  all  the 
higher  animals  at  least)  of  the  will  of  the  animal,  but  is  also  inde- 
pendent even  of  the  life  of  the  rest  of  the  body  ;  being  seen  after  the 
death  of  the  animal,  and  proceeding  with  perfect  regularity  in  parts 
separated  from  the  body.  Thus  isolated  epithelium-cells  have  been 
seen  to  swim  about  actively  in  water,  by  the  agency  of  their  cilia,  for 
some  hours  atler  they  have  been  detached  from  the  mucous  surface 
of  the  nose  ;  and  the  ciliary  movement  has  been  seen  fifteen  days 
after  death  in  the  body  of  a  Tortoise,  in  which  putrefaction  was  far 
advanced.     In  the  gills  of  the  River-Mussel,  which  are  among  the 


Vibratile  or  ciliated  Epithelium ;— a, 
nucleated  cells,  resting  on  their  smaller 
extremities;  b,  cilia. 


SIMPLE  ISOLATED  CELLS.— EPITHELIUM.  151 

best  objects  for  the  study  of  it,  the  movement  endures  with  similar 
pertinacity. 

235.  The  purpose  of  this  ciliary  movement  is  obviously  to  propel 
fluids  over  the  surface  on  which  it  takes  place ;  and  it  is  consequently 
limited  in  the  higher  animals  to  the  internal  surfaces  of  the  body,  and 
always  takes  place  in  the  direction  of  the  outlets,  towards  which  it 
aids  in  propelling  the  various  products  of  secretion.  The  case  is 
different,  however,  among  animals  of  the  lower  classes,  especially 
those  inhabiting  the  water.  Thus  the  external  surface  of  the  gills  of 
Fishes,  Tadpoles,  &c.,  is  furnished  with  cilia;  the  continual  move- 
ment of  which  renews  the  water  in  contact  with  them,  and  thus 
promotes  the  aeration  of  the  blood.  In  the  lower  Mollusca,  and  in 
many  Zoophytes,  which  pass  their  lives  rooted  to  one  spot,  the  motion 
of  the  cilia  serves  not  merely  to  produce  currents  for  respiration,  but 
likewise  to  draw  into  the  mouth  the  minute  particles  that  serve  as 
food.  And  in  the  free-moving  Animalcules,  of  various  kinds,  the 
cilia  are  the  sole  instruments  which  they  possess,  not  merely  for  pro- 
ducing those  currents  in  the  water  which  may  bring  them  the  requisite 
supply  of  air  and  food,  but  also  for  propelling  their  own  bodies  through 
the  water.  This  is  the  case,  too,  with  many  larger  animals  of  the 
class  Acalepha  (Jelly-fish),  which  move  through  the  water,  sometimes 
with  great  activity,  by  the  combined  action  of  the  vast  numbers  of 
cilia  that  clothe  the  margins  of  their  external  surfaces.  In  these  latter 
cases  it  would  seem  as  if  the  ciliary  movement  w^ere  more  under  the 
control  of  the  will  of  the  animal,  than  it  is  where  it  is  concerned  only 
in  the  organic  functions.  In  what  way  the  will  can  influence  it,  how- 
ever, it  does  not  seem  easy  to  say ;  since  the  ciliated  epithelium-cells 
appear  to  be  perfectly  disconnected  from  the  surface  on  which  they 
lie,  and  cannot,  therefore,  receive  any  direct  influence  from  their 
nerves.  Of  the  cause  of  the  movement  of  the  cilia  themselves,  no 
account  can  be  given  ;  they  are  usually  far  too  small  to  contain  even 
the  minutest  fibrillee  of  muscle  ;  and  we  must  regard  them  as  being, 
like  those  fibrillse,  organs  sui  generis,  having  their  own  peculiar  en- 
dowment,— which  is,  in  the  higher  animals  at  least,  that  of  continuing 
in  ceaseless  vibration,  during  the  whole  term  of  the  life  of  the  cells 
to  which  they  are  attached.  The  length  of  time  during  which  the 
ciliary  movement  continues  after  the  general  death  of  the  body,  is 
much  less  in  the  warm-blooded  than  in  the  cold-blooded  animals; 
and  in  this  respect  it  corresponds  with  the  degree  of  persistence  of 
muscular  irritability,  and  of  other  vital  endowments. 

236.  The  Tesselated-Epithelium,  as  already  mentioned,  covers  the 
Serous  and  Synovial  membranes,  the  lining  membrane  of  the  blood- 
vessels and  absorbents,  and  the  Mucous  membranes  with  their  glan- 
dular prolongations,  except  where  the  cylinder-epithelium  exists.  It 
presents  itself,  with  some  modifications  presently  to  be  noticed,  in  the 
ultimate  follicles  of  all  glands,  and  also  in  the  air-cells  of  the  lungs. 
In  this  latter  situation  it  is  furnished  with  cilia ;  and  these  are  also 
found  on  the  cells  of  the  tesselated-epithelium,  which  covers  the  deli- 


159  SIMPLE  ISOLATED  CELLS.—EPITHELIUM. 

cate  pia  mater  lining  the  cerebral  cavities. — The  Cylinder-Epithelium 
commences  at  the  cardiac  orifice  of  the  stomach,  and  lines  the  whole 
intestinal  tube;  and,  generally  speaking,  it  lines  the  larger  gland- 
ducts,  giving  place  to  the  tesselated  form  in  their  smaller  ramifica- 
tions. A  similar  epithelium,  furnished  with  cilia,  is  found  lining 
the  air-passages  and  their  various  offsets, — the  nasal  cavities,  frontal 
sinuses,  maxillary  antra,  lachrymal  ducts  and  sac,  the  posterior  surface 
of  the  pendulous  velum  of  the  palate  and  fauces,  the  Eustachian  tubes, 
the  larynx,  trachea,  and  bronchi, — becoming  continuous,  however, 
in  the  finer  divisions  of  the  latter,  with  the  ciliated  pavement-epi- 
thelium. The  upper  part  of  the  vagini,  the  uterus,  and  the  Fallopian 
tubes,  are  also  furnished  with  a  ciliated  Cylinder-epithelium.  The 
function  of  the  cilia  in  all  these  cases  appears  to  be  the  same ;  that  of 
propelling  the  viscid  secretions,  which  would  otherwise  accumulate 
on  these  membranes,  towards  the  exterior  orifices,  whence  they  may 
be  carried  off*. 

237.  The  simplest  office  which  the  Epithelium-cells  of  Mucous 
membranes  perform,  appears  to  be  that  of  elaborating  a  peculiar 
secretion,  termed  Mucus;  which  is  destined  to  protect  them  from  the 
contact  of  air,  or  from  that  of  the  various  irritating  substances  to 
which  they  are  exposed,  in  consequence  of  their  peculiar  position  and 
functions.  This  Mucus  is  a  transparent  semi-fluid  substance,  dis- 
tinguished by  its  peculiar  tenacity  or  viscidity.  It  is  quite  insoluble 
in  water ;  but  is  readily  dissolved  by  dilute  alkaline  solutions,  from 
which  it  is  precipitated  again  by  the  addition  of  an  acid.  A  substance 
resembling  Mucus  may  be  produced  from  any  fibrinous  exudation,  or 
even  from  pus,  by  treating  it  with  a  small  quantity  of  liquor  potassse. 
The  secretion  of  Mucus,  like  the  formation  of  Epidermis,  appears  to 
take  place  with  an  activity  proportioned  to  the  degree  of  irritation  of 
the  subjacent  membrane.  On  many  parts  of  the  mucous  surface,  a 
sufficient  supply  is  afforded  by  the  epithelium-cells  which  cover  it ; 
but  in  other  situations,  especially  along  the  alimentary  canal,  the 
demand  is  much  greater,  and  it  is  supplied  not  merely  by  the  cells 
of  the  surface,  but  by  those  lining  the  crypts  or  follicles  which  are 
formed  by  involutions  of  it.  There  is  reason  to  believe  that  the 
whole  epithelial  covering  of  the  stomach  and  intestinal  tube  (along 
the  upper  part  of  the  latter  at  least)  is  cast  oft' at  every  meal  (Fig.  27); 
the  cells  growing  from  their  germs,  elaborating  their  mucous  secretion, 
and  then  bursting  or  liquefying  to  set  this  free,  in  the  course  of  a  few 
hours.  The  debris  of  these  secreting  cells  may  be  recognized  in  the 
substances  voided  from  the  intestine  ;  as  well  as  in  the  mucus  taken 
from  the  surface  of  any  mucous  membrane. 

238.  The  Epithelium-cells,  which  are  thus  being  continually  re- 
newed on  the  Mucous  surfaces,  commonly  seem  to  have  their  origin 
in  the  granular  germs  diffused  through  the  basement-membrane  ;  but 
it  is  different  in  regard  to  the  cells  of  the  follicles,  which  seem  rather 
to  occupy  their  cavity  than  merely  to  line  their  walls,  and  which 
appear  to  be  in  course  of  continual  production  from  a  germinal  spot, 


SIMPLE  ISOLATED  CELLS.— SECRETING  CELLS.  153 

or  collection  of  reproductive  granules,  at  the  blind  extremity  of  the 
follicle.  This  is  the  case  in  the  ultimate  follicles  of  the  more  complex 
glands;  which  may  be  regarded  as  so  many  repetitions  of  the  simple 
crypts  or  follicles  in  the  substance  of  the  mucous  membranes ; — the 
only  difference  being,  that  the  former  pour  their  secretion  into  a 
branch  of  a  duct,  which  unites  with  the  other  ramifications  to  form 
a  trunk ;  and  this  trunk  conveys  them  to  their  destination  in  some 
cavity  lined  by  a  mucous  membrane ; — whilst  the  simple  follicles  or 
crypts  at  once  pour  forth  their  secretions  upon  the  surface  of  the 
membrane.     The  accompanying  figure  represents  two  follicles  of  the 

Fig.  23.  Fig  24. 


Two  follicles  from  the  liver  of  Carcmt«  Ultimate    follicles  of  Mammary 

mcBnas,  (Common  Crab),  with  their  con-  gland,  with  their  secreting  cells,  a, 

tained  secreting  cells.  «;— *,  b,  the  nuclei. 

liver  of  the  Common  Crab,  which  are  seen  to  be  filled  with  secreting 
cells ;  it  is  evident,  from  the  comparative  sizes  of  these  cells  in  dif- 
ferent parts,  that  they  originate  at  the  blind  extremity  of  the  follicle, 
where  there  is  a  germinal  spot;  and  that,  as  they  recede  from  that 
spot,  they  gradually  increase  in  size,  and  become  filled  wath  their 
characteristic  secretion,  being  at  the  same  time  pushed  onwards 
towards  the  outlet  by  the  continual  new  growth  of  cells  at  the  ger- 
minal spot.  In  Fig.  24  are  shown  the  corresponding  ultimate  folli- 
cles of  the  Mammary  gland  ;  filled,  like  the  preceding,  wuth  secreting 
cells. 

239.  The  whole  of  the  acts,  then,  by  which  the  separation  of  the 
different  Secretions  from  the  Circulating  fluid  is  accomplished,  really 
consist  in  the  growth  and  nutrition  of  a  certain  set  of  cells,  usually 
covering  the  free  surfaces  of  the  body,  both  internal  and  external,  or 
lining  cavities  which  have  a  ready  communication  with  these  by 
means  of  ducts  or  canals.*  These  cells  differ  widely  from  one  an- 
other, in  regard  to  the  kind  of  matter  which  they  appropriate  and 
assemble  in  their  cavities;  although  the  nature  of  their  walls  is  pro- 
bably the  same  throughout.  Thus  we  find  biliary  matter  and  oil, 
easily  recognizable  by  their  colour  and  refracting  power,  in  the  cells 
of  the  liver;  milk  in  the  cells  of  the  mammary  gland  ;  sebaceous  or 
fatty  matter  in  the  cells  of  the  sebaceous  follicles  of  the  skin  ;  and  so 
on.  All  these  substances  are  derived  from  the  blood ;  being  either 
contained  in  it  previously,  or  being  elaborated  from  its  constituents 

*  The  Synovial  secretion  is,  perhaps,  the  only  one  which  is  poured  into  a  closed 
sac. 


154 


SIMPLE  ISOLATED  CELLS^-REPRODUCTIVE  CELLS. 


by  a  simple  process  of  transformation, — as,  for  exam]5le,  that  which 
converts  the  albumen  of  the  blood  into  the  casein  of  milk.  Hence 
they  may  be  considered  as  the  peculiar  aliments  of  the  several  groups 
of  cells  ;  whose  acts  of  nutrition  are  the  means  of  drawing  them  off 
or  secreting  them,  from  the  general  circulating  fluid. 
When  they  have  attained  their  full  growth,  and  ac- 
complished their  term  of  life,  their  walls  either  burst 
or  dissolve  away,  and  thus  the  contents  of  the  cells 
are  delivered  into  the  cavity,  or  upon  the  surface,  at 
which  they  are  required.  Now  as  all  the  canals  of 
the  glands  open  either  directly  outwards  upon  the 


Fig.  25. 


Secreting  cells  of 
Human  Liver;  a,  nu- 
cleus; ft,  nucleolus;  c, 
oil-particles. 


surface,  or  into  cavities  which  communicate  with 


the  exterior,  it  is  evident  that  the  various  products 
of  the  action  of  these  epithelial  cells  must  be  destined 
to  be  cast  forth  from  the  body.  This  we  shall  find  to  be  the  case ; 
some  of  them,  as  the  bile  and  urine,  being  excretions,  of  which  it  is 
necessary  to  get  rid  by  the  most  direct  channel ;  whilst  others,  like 
the  tears,  the  saliva,  the  gastric  fluid,  the  milk,  &c.,  are  separated 
from  the  blood,  not  so  much  for  its  purification,  but  because  they  are 
required  to  answer  certain  purposes  in  the  economy. 

240.  Now  whilst  thus  actively  concerned  in  the  Nutritive  functions 
of  the  economy,  and  exercising  in  the  highest  degree  their  powers  of 
selection  and  transformation,  these  Secreting  cells  appear  to  have 
nothing  to  do  with  the  operation  of  Reproduction.  We  have  seen 
that  they  do  not  even  regenerate  themselves ;  all  their  energies  being, 
as  it  were,  concentrated  upon  their  own  growth ;  and  the  successive 
production  of  new  generations  being  provided  for  by  other  means. 
But  special  Reproductive  cells,  destined  to  furnish  the  germs  for  the 
continuance   of  the  race,  are  not  wanting.     These  are   developed 

within  the  tubuli  of  the  Testicle  ;  where 
they  appear  to  hold  exactly  the  same 
relation  to  the  membranous  walls  of 
those  tubuli,  as  do  the  secreting  cells 
to  the  tubes  and  follicles  of  the  proper 
Glands.  The  contents  of  these  repro- 
ductive cells  are  peculiarly  granular; 
and  the  granules  are  at  one  time  dif- 
fused through  the  entire  cell.  They 
are  afterwards  seen,  however,  to  pre- 
sent a  regular  linear  arrangement ; 
forming  a  bundle  of  fibrous  bodies,  still 
comprehended,  however,  within  the 
cell.  After  a  time,  however,  the  con- 
taining cells  burst,  and  the  fibrous 
bodies  within  separate  and  are  set  free. 
From  the  very  peculiar  motion  which  they  possess,  they  were  long 
regarded  as  distinct  Animalcules,  and  received  the  designation  of 
Spermatozoa.     It  is  now  generally  admitted,  however,  that  they  have 


Fig.  26. 


Formation  of  Spermatozoa  within  semi- 
nal cells  ;  a.  the  original  nucleated  cell ;  6, 
the  same  enlarged,  with  the  formation  of 
the  Spermatozoa  in  progress  ;  c,  the  Sper- 
matozoa nearly  complete,  but  still  enclosed 
within  the  cell. 


SIMPLE  ISOLATED  CELLS.— ABSORBENT  CELLS.  155 

no  more  claim  to  a  distinct  animal  character,  than  have  the  ciliated 
epithelia  of  mucous  membrane,  which  will  likewise  continue  in  move- 
ment when  separated  from  the  body.  The  so-called  Spermatozoa 
appear  to  be  nothing  else  than  cell-germs,  furnished  with  a  peculiar 
power  of  movement,  by  means  of  which  they  are  enabled  to  make 
their  way  into  the  situation  where  they  may  be  received,  cherished, 
and  developed, — as  will  be  shown  hereafter.  (Chap.  XT.)  It  is  a 
curious  fact  that  the  seminal  cells,  in  which  the  Spermatozoa  are 
formed,  are  sometimes  ejected  from  the  gland,  not  only  before  they 
have  burst  and  set  free  the  Spermatozoa,  but  even  long  before  the 
development  of  the  Spermatozoa  in  their  interior  is  completed; — thus 
affording  a  complete  demonstration  of  their  independent  vitality. 

241.  We  now  proceed  to  a  class  of  cells,  which  are  equally 
independent  of  each  other,  which  begin  and  end  their  lives  as  cells, 
without  undergoing  any  transformation,  but  which  form  part  of  the 
substance  of  the  fabric,  instead  of  lying  upon  its  free  surfaces  and 
being  continually  cast  off  from  them.  Still  their  individual  history  is 
much  the  same  as  that  of  the  cells  already  noticed ;  and  they  differ 
chiefly  in  regard  to  the  destination  of  their  products. — The  first  group 
of  this  class  deserving  a  separate  notice,  is  that  which  effects  the 
introduction  of  aliment  into  the  body; — of  those  kinds  of  aliment,  at 
least,  which  are  not  received  in  solution  by  any  more  direct  means. 
Along  the  greater  part  of  the  intestinal  tube,  from  the  point  at  which 
the  hepatic  and  pancreatic  ducts  enter  it,  to  the  rectum,  we  find  the 
mucous  membrane  furnished  with  a  vast  number  of  minute  tufts  or 
folds,  by  which  its  free  surface  is  vastly  extended ;  these  are  termed 
villi.  They  may  be  compared  to  the  ultimate  root-fibres  of  trees,  both 
in  structure  and  function ;  for  each  of  them  gives  origin  to  a  minute 
lacteal  or  chyle-absorbing  vessel,  which  occupies  its  centre ;  whilst 
it  also  contains  a  copious  network  of  blood-vessels,  (Fig.  8,  p.  118,) 
which  appears  likewise  to  participate  in  the  act  of  absorption,  by 
taking  up  substances  that  are  in  complete  solution.  Now  at  the  end 
of  every  villus,  there  may  be  seen,  whilst  the  process  of  digestion 
and  absorption  is  going  on,  a  cluster  of  minute  cells,  in  the  midst  of 
which  the  origin  of  the  lacteal  is  lost.  These  cells,  whose  size  varies 
from  1-lOOOth  to  l-2000th  of  an  inch,  are  turgid  with  a  milky  fluid, 
which  is  evidently  the  same  with  that  which  is  found  in  the  lacteals ; 
and  there  is  good  reason  to  believe,  that  it  is  by  the  growth  and 
nutrition  of  these  cells,  that  this  milky  fluid,  the  chyle,  is  selected 
from  the  contents  of  the  digestive  cavity.  Their  function,  therefore,  is 
precisely  the  converse  of  that  of  the  secreting  cells  already  described; 
whilst  the  history  of  their  individual  lives  is  the  same.  These  absor- 
bent cells  draw  their  materials  from  the  fluid  in  the  digestive  cavity, 
instead  of  from  the  blood ;  and  when  they  burst  or  liquefy,  they  set 
free  their  contents  where  they  may  be  taken  up  by  a  lacteal  and  con- 
veyed into  the  circulating  current,  instead  of  pouring  them  into  a 
cavity  through  which  they  will  be  shortly  expelled. 

242.  In  the  intervals  of  the  digestive  process,  the  extremities  of  the 


156 


ABSORBENT  CELLS. 


villi  are  comparatively  flaccid  ;  and  instead  of  cells,  they  show  merely 
a  collection  of  granular  germs.  These  begin  to  develop  themselves, 
as  soon  as  the  food  has  been  dissolved  in  the  stomach  and  transmitted 
to  the  intestine;  and  their  development  goes  on,  as  long  as  the  villi 
are  surrounded  with  nutrient  matter.  The  cells  rapidly  grow,  select, 
absorb,  and  prepare  the  nutritious  matter,  by  making  it  a  part  of 
themselves;  and,  when  their  work  is  accomplished,  they  deliver  it  to 
the  lacteals  by  their  own  rupture  or  deliquescence.  The  accompany- 
ing diagrams  represent  the  comparative  condition  of  the  Mucous 

Fig.  27. 


Diagram  of  mucous  membrane  during  diges- 
tion and  absorption  of  chyle;  a,  a  villus,  turgid 
and  erect;  its  protective  epithelium  cast  off  from 
its  free  extremity;  its  absorbent  vesicles,  its  lac- 
teals, and  its  blood-vessels  turbid ;  b,  a  follicle 
discharging  its  secreting  epithelial  cells. 


Diagram  of  mucous  membrane  of  jejunum, 
when  Absorption  is  not  going  on ;  a,  protec- 
tive epithelium  of  a  villus;  &,  secreting  epi- 
thelium of  a  follicle ;  c,  c,  c,  primary  membrane, 
■with  its  germinal  spots  or  nuclei,  d,  d;  e, 
germs  of  absorbent  vesicles;/,  vessels  and 
lacteals  of  villus. 


membrane,  its  villi,  and  its  secreting  follicles,  during  the  time  when 
absorption  is  going  on,  and  in  the  intervals  of  the  process.  It  will 
be  seen  that,  in  the  former  state,  the  epithelium-cells  are  not  only 
being  cast  off  from  the  free  surface  of  the  membrane,  and  from  the 
interior  of  the  follicles ;  but  they  are  also  detached  from  the  surface 
of  the  villus,  that  they  may  offer  no  impediment  to  the  process  of 
absorption.  During  the  intervals  of  digestion,  the  secreting  epithe- 
lium of  the  follicles,  and  the  protective  epithelium  of  the  villi,  are 
alike  renewed,  from  the  germs  supplied  by  the  basement-membrane. 
243.  Although  the  mucous  membrane  of  the  intestinal  tube  is  the 
only  channel  through  which  insoluble  nutriment  can  be  absorbed  in 
the  completely-formed  Mammal,  and  the  only  situation,  therefore,  in 
which  w^e  meet  with  these  absorbent  cells,  there  are  other  situations 
in  which  similar  cells  perform  analogous  duties  in  the  embryo.  Thus 
the  Chick  derives  its  nutriment,  whilst  in  the  egg,  from  the  substance 
of  the  yelk,  by  absorption  through  the  blood-vessels  spread  out  in  the 
vascular  layer  of  the  germinal  membrane  surrounding  the  yelk ;  which 
vessels  answer  to  the  blood-vessels  and  lacteals  of  the  permanent 
digestive  cavity,  and  are  raised  into  folds  or  villi  as  the  contents  of 
the  yelk-bag  are  diminished.  Now  the  ends  of  the  vessels  are  sepa- 
rated from  the  fluid  contents  of  the  yelk-bag,  by  a  layer  of  cells ; 


ABSORBENT  CELLS. 


157 


which  seems  to  have  for  its  object  to  select  and  prepare  the  materials 
supplied  by  the  yelk,  for  being  received  into  the  absorbent  vessels. 

244.  In  like  manner,  the  embryo  of  the  Mammal  is  nourished,  up 
to  the  time  of  its  birth,  through  the  medium  of  its  umbilical  vessels ; 
the  ramifications  of  which  form  tufts,  that  dip  down,  as  it  were,  into 
the  maternal  blood,  and  receive  from  it  the  materials  destined  to  the 
nutrition  of  the  foetus;  besides  effecting  the  aeration  of  the  blood  of 
the  latter,  by  exposing  it  to  the  more  oxygenated  blood  of  the  mother. 
Now  around  the  capillary  loop  of  the  fcetal  tuft,  there  is  a  layer  of 
cells,  closely  resembling  the  absorbent  cells  of  the  villi ;  and  these 
are  enclosed  in  a  cap  of  basement-membrane,  which  completes  the 
foetal  portion  of  the  tuft,  and  renders  it  comparable  in  all  essential 
respects  to  the  intestinal  villus.  It  is  again  surrounded,  however,  by 
another  layer  of  membrane  and  of  cells,  belonging  to  the  maternal 
system ; — the  derivation  and  arrangement  of  which  will  be  explained 
hereafter.     The  maternal  cells  (6,  Fig.  29)  may  be  regarded  as  the 

Fig.  29. 


Extremity  of  a  placental  villus:— a,  external  membrane  of  the 
villus,  continuous  with  the  lining  membrane  of  the  vascular  system 
of  the  mother;  b,  external  cells  of  the  villus,  belonging  to  the  pla- 
cental decidua ;  c,  c,  germinal  centres  of  the  external  cells ;  d,  the 
space  between  the  maternal  and  fecial  portions  of  the  villus;  e,  the 
internal  membrane  of  the  villus,  continuous  with  the  external 
membrane  of  the  chorion;/,  the  internal  cells  of  the  villus,  belong- 
ing to  the  chorion;  g,  tlie  loop  of  umbilical  vessels. 


first  selectors  of  nutriment  from  the  circulating  fluid  of  the  parent:  the 
materials,  partially  prepared  by  them,  are  poured  into  the  cavity  (d) 
surrounding  the  extremity  of  the  tuft;  and  from  this  they  are  taken 
up  by  the  foetal  cells  {/),  which  further  elaborate  them,  and  impart 
them  to  the  capillary  loop  (g)  of  the  umbilical  vessels. 

245.  Thus  we  see  that  the  several  functions  of  Selection,  Absorp- 
tion, Assimilation,  Respiration,  Secretion,  and  Reproduction,  are 
performed  by  the  agency  of  cells  in  the  Animal  as  in  the  Vegetable 
kingdom, — in  the  complex  Human  organism,  as  in  the  humblest 
Cryptogamic  Plant ;  the  only  difference  being,  that  in  the  latter  there 
is  a  greater  division  of  labour,  different  groups  of  cells  being  appro- 
priated to  different  functions,  in  the  general  economy,  whilst  the 
history  of  their  own  processes  of  nutrition  and  decay  is  everywhere 
essentially  the  same.  Thus  we  have  seen  that  the  Absorbent  cells,  at 
the  extremities  of  the  intestinal  or  placental  villi,  select  and  draw  into 
themselves,  as  the  materials  of  their  own  growth,  certain  substances 
in  their  neighbourhood  ;  which  are  still  as  much  external  to  the  tissues 
of  the  body,  as  are  the  fluids  surrounding  the  roots  of  plants.  Having 
come  to  their  full  term  of  life,  they  burst  or  dissolve  away,  and  give 
up  their  contents  to  the  absorbent  vessels,  which  carry  them  into  the 
general  current  of  the  circulation,  where  they  are  mingled  with  the 
fluid  previously  assimilated, — the  blood.  Whilst  passing  through  the 
vessels,  they  are  subjected  to  the  action  of  another  set  of  cells,  (the 


158  SIMPLE  ISOLATED  CELLS. 

lymph  and  cbyle-corpuscles,  and  the  colourless  corpuscles  of  the 
blood,)  by  which  they  are  gradually  assimilated,  or  converted  into  a 
substance  of  a  more  directly  organizable  character ;  these  assimilating 
cells  being  developed  from  germs  that  float  in  the  fluid,  drawing  into 
themselves  the  albuminous  matter,  converting  it  into  fibrin,  and  then 
setting  it  free  by  their  own  dissolution.  In  the  same  fluid  another 
set  of  cells,  the  red  corpuscles  of  the  blood,  are  observed  to  float,  in 
the  higher  classes  of  animals ;  whose  special  function  appears  to  be 
the  conveyance  of  oxygen  from  the  lungs  to  the  tissues,  and  of  car- 
bonic acid  from  the  tissues  to  the  lungs;  in  other  words,  that  of 
Respiration:  these  cells  do  not  appear  to  pass  through  their  course  of 
existence  as  rapidly  as  the  preceding.  Next  we  have  various  groups 
of  cells,  external  to  the  vessels,  on  the  free  surfaces  of  the  body; 
whose  oflSce  it  is  to  draw  from  the  blood  certain  materials,  which  are 
destined  for  Secretion  or  separation  from  it ;  either  for  the  sake  of 
preserving  that  fluid  in  its  requisite  purity,  or  for  answering  some 
other  purpose  in  the  system.  These  cells  grow  at  the  expense  of  the 
substances,  w^hich  they  draw  into  themselves  from  the  blood ;  and  on 
their  dissolution,  they  cast  forth  their  contents  on  the  free  surfaces 
communicating  with  the  exterior  of  the  body,  to  which  they  are  in 
time  conveyed.  And,  lastly,  we  have  a  special  set  of  cells,  destined 
to  prepare  the  germs  of  new  beings ;  which  are,  in  like  manner,  set 
free  by  the  rupture  of  the  parent-cell,  in  a  condition  that  enables 
them  to  be  conveyed  to  a  place  appropriated  for  their  further  develop- 
ment, and  thus  to  perform  the  essential  part  of  the  process  of  Repro- 
duction. 

246.  The  cells  which  are  thus  the  active  instruments  of  the  Organic 
functions,  are  produced  and  succeed  one  another  with  a  rapidity  pro- 
portional to  the  energy  of  those  functions.  The  causes  which  influence 
their  growth  and  decay  are  not  always  evident;  thus  we  occasionally 
find  an  extraordinary  tendency  to  the  elaboration  of  Fibrin,  as  mani- 
fested in  the  increase  in  the  proportion  of  that  ingredient  of  the  blood, 
and  in  the  number  of  the  Assimilating  cells  or  white  corpuscles  that 
float  in  that  fluid  ;  and  as  to  the  causes  of  this  condition,  which  is  one 
important  part  of  the  disordered  state  termed  Inflammation,  we  are 
almost  entirely  in  the  dark.  The  development  of  the  Absorbent  cells 
appears  to  depend  upon  the  supply  of  alimentary  materials  afforded 
by  the  contents  of  the  digestive  cavity ;  and  also  upon  the  supply  of 
blood  furnished  by  the  capillaries  of  the  villi,  from  which  last  the 
materials  of  the  cell-walls  are  probably  derived.  The  conditions  of 
the  development  of  the  Secreting  cells  are  not  sufficiently  understood  ; 
it  does  not  appear  to  depend  solely  upon  the  supply  of  their  materials ; 
for,  as  we  shall  see  hereafter,  these  materials  may  accumulate  unduly 
in  the  blood,  through  the  insufficient  production  of  the  cells  which 
are  destined  to  separate  them ;  whilst,  on  the  other  hand,  the  presence 
of  certain  substances  in  the  blood  appears  to  accelerate  their  develop- 
ment. Of  these  stimuli.  Mercury  is  one  of  the  most  powerful ;  and 
we  have  continual  opp©rtuniti€s  of  witnessing  its  effects,  in  giving  an 


CELLS  CONNECTED  TOGETHER  IN  SOLID  TISSUES.  159 

increased  activity  to  the  secreting  actions.  There  is  probably  not  a 
gland  in  the  body,  which  is  not  in  some  degree  influenced  by  its  pre- 
sence in  the  blood  ;  but  the  liver,  the  kidneys,  the  salivary  glands, 
and  the  glandulae  of  the  intestinal  canal,  appear  to  be  those  most 
affected  by  its  stimulating  powers.  The  action  of  the  glands,  in  other 
words  the  development  of  the  secreting  cells,  appears  to  be  influenced 
by  mental  emotions ;  being  sometimes  accelerated,  and  sometimes 
retarded,  through  their  agency.  This  is  especially  the  case  in  regard 
to  the  secretion  of  Milk,  Tears,  Saliva,  and  Gastric  juice.  But  we 
shall  hereafter  see  that  the  influence  thus  manifested  is  probably 
exerted  through  the  capillary  circulation,  which  is  known  to  be  power- 
fully affected  by  mental  emotions,  as  in  the  acts  of  blushing  and  erec- 
tion ;  and  that  the  increased  production  of  the  secretion  is  immediately 
due  to  the  increased  flow  of  blood  to  the  gland.  We  have  an  example 
of  this,  in  the  "  draught"  (as  it  is  termed)  experienced  by  Nurses, 
when  the  child  is  applied  to  the  breast ;  which  is  a  perceptible  rush 
of  blood  into  the  organ. 

5.   Of  Cells  connected  together  as  permanent  constituents  of  the  Tissues. 

247.  We  now  pass  on  to  consider  those  Cells  which  enter  as  com- 
ponent elements  into  the  solid  and  permanent  fabric  of  the  body,  and 
which  do  not  take  so  active  a  part  in  its  vital  operations.  These  we 
shall  find  to  be  usually  more  or  less  closely  connected  together,  either 
by  a  general  enveloping  membrane,  or  by  an  intercellular  substance, 
which  is  interposed  between  their  walls,  and  holds  them  together  by 
its  adhesive  properties.  Before  entering  upon  the  description  of  the 
tissues  thus  formed,  it  will  be  desirable  to  consider  a  little  more  fully 
the  mode  in  which  the  component  cells  are  developed,  and  the  cha- 
racter of  the  transformations  they  may  undergo. 

248.  We  have  seen  that  a  minute  isolated  molecule,  prepared  by  a 
parent-cell,  and  set  free  by  its  dissolution,  may  become  the  germ  of  a 
new  cell ;  and  that  the  assimilating  cells  which  float  in  the  animal  fluids 
seem  to  have  their  origin,  like  the  equally-simple  cells  of  the  Yeast- 
fungus,  in  such  floating  germs ;  whilst  the  epithelial  and  epidermic 
tissues  arise  from  similar  granules  diffused  through  the  substance  of 
the  basement-membrane,  or  aggregated  in  its  germinal  spots.  But  the 
usual  mode  of  development  of  the  cells  of  a  higher  and  more  perma- 
nent character,  is  somewhat  different ;  for  these  are  developed  within 
the  parent-cell,  which,  instead  of  dissolving  away,  may  remain  as  a 
thin  membrane  around  them ; — all  traces  of  it,  however,  at  last 
disappearing,  in  consequence  of  the  distension  which  it  undergoes. 
Even  whilst  still  evidently  contained  within  the  parent-cell,  the 
secondary  cells  may  themselves  be  developing  a  third  generation 
within  them.  The  rapidity  of  the  process,  and  th«  number  of  cells 
thus  developed,  appear  to  bear  a  close  relation  with  the  transitory  or 
permanent  character  of  the  structure.  It  is  in  Cancerous  growths, 
that  we  meet  with  the  most  remarkable  examples  of  rapid  production  ; 


160 


CELLS  CONNECTED  TOGETHER  IN  SOLID  TISSUES. 


Fig.  30. 


Parent-cells,  a,  a,  of  cancer- 
ous structure,  containing  se- 
condary cells,  b,  b,  each  having 
one,  two,  or  three  nuclei,  c,  c. 


a  large  number  of  secondary  cells  being  developed  within  each  pri- 
mary ;  these  secondary  cells  again  becoming  the  parents,  each  one  of 
an  equally  large  generation  ;  and  so  on.  Here 
the  whole  energy  seems  concentrated  upon 
the  reproductive  process ;  and  we  find  that 
growths  composed  of  such  cells  have  a  very 
rapid  increase,  but  very  little  solidity  or  per- 
manence.— On  the  other  hand  we  find  that, 
in  structures  which  are  destined  to  undergo 
a  higher  development,  and  to  possess  a  more 
permanent  character,  the  number  of  cells 
developed  within  each  parent  is  more  limit- 
ed ;  thus  in  the  early  development  of  the 
embryo  of  Mammalia  it  is  limited  to  two; 
and  the  first  pair  of  cells  is  thus  progressively 
developed  into  four,  eight,  sixteen,  and  so 
on.  The  same  tendency  to  a  binary  multiplication  is  apparent  also 
in  the  cells  of  Cartilage  (§  267) ;  and  it  probably  exists  also  in  other 
cellular  structures  of  a  permanent  character. 

249.  It  is  most  coipmonly  to  be  observed  in  these  cells,  that  the 
reproductive  granules,  instead  of  being  diffused  throughout  the  cavity 
of  the  cell, — as  they  are  in  the  cells  of  the  Cryptogamic  Plants,  the 
White  Corpuscles  of  the  blood  of  Animals,  &c.  &c., — are  concen- 
trated in  one  spot,  forming  a  nucleus  (Figs.  20,  21);  and  it  is  from 
this  nucleus  that  the  new  cells  originate.  The  granules  appear  to 
undergo  the  same  changes,  when  developed  in  this  situation,  as  they 
do  when  isolated  within  the  cell,  or  altogether  set  free ;  at  first  they 
show  a  simple  enlargement,  looking  like  little  warts  projecting  into 
the  cell ;  this  enlargement  continues,  until  the  difference  between  the 
cell-wall  and  the  cavity,  the  containing  and  the  contained  parts, 
becomes  perceptible ;  and  the  character  of  the  young  cell  is  then 
obvious. 

250.  According  to  Dr.  Barry's  observations  on  the  processes  of 
cell-growth  in  the  germinal  vesicle  and  early  embryo  of  the  Rabbit, 
it  is  the  outer  circle  of  granules  forming  the  nucleus,  which  is  first 
developed  into  young  cells ;  the  next  then  commences,  and  pushes 
outwards  the  ring  of  cells  previously  formed;  and  by  the  continuance 
of  the  same  process,  the  parent-cell  may  be  completely  filled  with  a 
new  generation.  Of  these,  however,  the  greater  part  may  be  destined 
to  liquefy  or  dissolve  away;  their  office  having  apparently  been,  to 
assimilate  or  prepare  the  materials  that  are  destined  for  the  nutrition 
of  the  permanent  ofispring,  which  are  the  cells  latest  formed  in  the 
centre  of  the  nucleus.  A  pellucid  spot,  which  is  frequently  seen  in 
the  centre  of  the  nucleus,  has  received  the  name  of  nucleolus  (Fig. 
20,  c);  sometimes  two  or  even  three  nucleoli  may  be  seen  in  a  single 
nucleus  (Fig.  21,  a).  The  cause  of  this  appearance  is  not  precisely 
understood  ;  but  it  seems  to  be  of  a  transitory  character,  indicating  a 
certain  stage  in  the  conversion  of  the  nucleus  into  new  cells. 


CELLS  CONNECTED  TOGETHER  IN  SOLID  TISSUES.  161 

251.  The  function  of  the  nucleus  in  the  development  of  new  cells, 
is  thus  evidently  identical  with  that  of  the  "  germinal  spots"  already 
described  as  existing  at  the  extremity  of  the  secreting  follicles  (§  238), 
or  in  the  substance  of  the  basement-membrane.  In  fact'we  are  pro- 
bably to  regard  each  secreting  follicle  as  a  large  parent-cell ;  of  which 
the  functions  are  permanent,  instead  of  transitory ;  and  which,  having 
opened  into  a  neighbouring  duct,  instead  of  remaining  closed,  con- 
tinues to  develop  new  secondary  or  secreting  cells,  from  the  nucleus 
or  germinal  spot  at  its  opposite  extremity,  to  an  unlimited  extent. 
And  it  is  probable,  also,  that  the  "  germinal  spots"  in  the  substance  of 
the  basement-membrane  are  really  the  nuclei  of  cells,  by  the  coales- 
cence of  which  it  is  formed,  in  the  manner  to  be  presently  noticed. 

252.  Now  if  the  walls  of  the  parent-cells,  instead  of  liquefying  or 
thinning  away,  are  thickened  or  strengthened  by  additional  nutrition, 
they  may  remain  as  permanent  vesicles,  enclosing  and  holding  together 
numerous  secondary  cells;  and  this  appears  to  be  the  case  in  Adipose 
tissue,  and  also  in  tumours  of  various  kinds. 

253.  Where  such  enveloping  membranes  are  wanting,  we  fre- 
quently find  the  component  cells  of  the  permanent  tissues  of  Animals 
(Rke  those  of  the  higher  plants)  held  together  by  an  intercellular  sub- 
stance ;  which  generally  presents  no  distinct  traces  of  organization ; 
and  which  usually  consists  of  Gelatin,  or  of  a  substance  allied  to  it  in 
composition.  The  proportion  of  this  substance  to  the  cells  may  vary 
in  different  cases  ;  and  very  different  characters  may  thus  be  presented 
by  a  tissue  made  up  of  the  same  elements.  Thus  the  subjoined  figure 
represents  a  portion  of  one  of  the  animal  layers  included  between  the 
calcareous  laminse  of  a  bivalve  shell ;  in  which  we  see  on  the  one  side 
a  number  of  nuclei  or  incipient  cells,  scattered  through  a  bed  of  homo- 
geneous intercellular  substance,  and  bearing  but  a  very  small  propor- 
tion to  it;  whilst  the  opposite  end  exhibits  a  set  of  polygonal  cells,  in 
close  contact  with  each  other,  the  intercellular  substance  being  only 
represented  by  the  thick  dark  lines,  which  mark  the  boundaries  of  the 
cells,  and  which  are  rather  thicker  at  the  angles  of  the  latter.  Between 
these  two  extremes,  we  observe  every  stage  of  transition. 

254.  The  presence  of  a  very  large  amount  of  intercellular  substance, 
through  which  minute  cells  are  scattered  at  considerable  intervals, 
(Fig.  31,  a,)  is  characteristic  of  various  forms  of  Cartilage;  and  more 
particularly  of  that  soft  semi-cartilaginous  structure,  of  which  the 
Jelly-fish  are  for  the  most  part  composed.  In  other  forms  of  cartilage, 
we  find  the  cells  more  developed,  and  in  closer  proximity  to  each 
other,  the  proportion  of  the  intercellular  substance  being  at  the  same 
time  diminished  (as  seen  at  h  and  c.  Fig.  31) ;  but  it  is  not  often, 
save  in  embryonic  structures,  that  we  find  the  cells  in  such  close 
proximity,  and  the  intercellular  substance  so  nearly  wanting,  as  at  d. 
Such  examples  do  occasionally  present  themselves,  however,  even  in 
the  soft  tissues.  Thus  the  chorda  dorsalis,  which  replaces  the  verte- 
bral column  in  the  lowest  Fishes,  and  of  which  the  analogue  is  found 
in  the  embryos  of  the  higher  Vertebrata,  is  made  up  of  a  structure  of 


162 


CELLS  CONNECTED  TOGETHER  IN  SOLID  TISSUES. 


this  kind.  The  true  Skin,  in  the  Short  Sun-fish,  is  replaced  by  a 
similar  layer  of  cellular  tissue,  which  extends  over  the  whole  body, 
varying  in  thickness  from  one-fourth  of  an  inch  to  six  inches.     And 

Fig.  31. 


Portion  of  shell-membrane,  showing  theorigin  of  cells  in  the  midst  of  horny  intercellular  substance; 
a,  nuclei;  b,  incipient  cells;  c,  the  same  further  advanced,  but  separated  by  intercellular  substance 
d,  the  cells  become  polygonal  by  mutual  pressure. 

in  the  Lancelot  (a  little  fish  which  is  destitute  of  so  many  of  the 
characters  of  a  Vertebrated  animal,  that  its  right  to  a  place  in  that 
division  has  been  doubted),  a  considerable  portion  of  the  fabric  is 
made  up  of  a  similar  parenchyma. 

255.  Now  we  shall  find  that  one  method,  by  which  the  requisite 
firmness  and  solidity  are  given  to  the  animal  fabric,  consists  in  the 
deposition  of  earthy  substances  in  the  interior  of  such  cells,  by  a  peculiar 
secreting  action  of  their  own.  Thus  in  Shell,  we  find  them  completely 
filled  up  with  carbonate  of  lime ;  and  in  Bones  and  Teeth  with  car- 
bonate and  phosphate  of  lime.  When  this  is  the  case,  there  is  a 
tendency  to  an  apparent  coalescence  of  the  cells,  by  the  obliteration  of 
their  partitions ;  or  rather,  perhaps,  by  the  removal  of  the  whole 
intercellular  substance  from  between  them,  the  actual  cell-walls  being 
so  very  thin,  that  they  are  not  distinguishable.  The  incipient  stages 
of  this  coalescence,  as  seen  in  another  portion  of  the  same  membrane 
as  that  represented  in  the  last  figure,  are  shown  in  Fig.  32.     At  a. 


Fig.  32. 


Portion  of  shell-membrane,  showing  the  gradual  coalescence  of  distinct  cells ;  at  a,  the  cells  sepa- 
rated by  iatercellular  substance ;  at  6,  the  partitions  are  thinner ;  and  at  c,  they  almost  disappear. 


COALESCENCE  AND  METAMORPHOSIS  OF  CELLS.  163 

the  nucleated  cells  are  very  distinct;  and  are  separated  by  a  large 
quantity  of  intercellular  substance.  At  b,  they  approach  each  other 
more  closely,  the  amount  of  intercellular  substance  being  less  ;  the 
widest  intervals  are  seen  at  the  angles  of  the  cells.  At  c,  the  approxi- 
mation is  much  closer ;  and  the  cell-walls  are  scarcely  distinguishable 
at  the  points  where  they  come  into  immediate  contact.  Proceeding 
further,  we  observe  that  the  partitions  are  much  less  complete ;  so 
that  the  originally  distinct  cellular  character  of  the  membrane  is  chiefly 
indicated  by  the  bright  nuclei,  which  are  regularly  dispersed  through 
it,  and  by  the  triangular  dark  spots,  which  show  the  remains  of  the 
intercellular  substance  at  the  angles  where  three  cells  join  each  other. 
The  coalescence  may  be  traced  further  than  it  is  shown  to  do  in  the 
figure  ;  so  that,  if  it  were  not  for  the  evidence  afforded  by  the  transi- 
tion-stages here  represented,  it  would  be  difficult  to  prove  that  the 
membranous  layer  had  its  origin  in  cells. 

256.  These  facts,  respecting  the  gradual  coalescence  of  cells,  ex- 
plain not  merely  the  appearances  presented  in  Tooth,  Shell,  &c. 
(hereafter  to  be  described) ;  but  also  those  which  are  exhibited  by 
the  Basement-membrane,  as  already  detailed  (§  206.) 

257.  There  is  no  evidence,  in  the  preceding  case,  that  the  cavities 
of  the  cells  coalesce ;  and  there  is  no  reason  why  they  should  do  so. 
But  we  often  find  such  an  union,  where  the  production  of  a  continuous 
tube  is  required.  The  long  straight  open  ducts,  through  which  the  sap 
of  Plants  rises  in  the  stem,  are  unquestionably  formed  by  a  coalescence 
of  the  cavities  of  cells  of  a  cylindrical  form,  placed  regularly  end  to 
end ;  and  it  seems  probable  that  the  network  of  anastomosing  vessels, 
through  which  the  elaborated  sap  finds  its  way  to  the  various  parts  of 
the  vegetable  fabric,  is  formed,  in  like  manner,  by  the  coalescence  of 
cells,  arranged  obliquely  and  transversely  in  regard  to  one  another. 
In  like  manner,  the  capillary  Blood-vessels  of  Animals  are  usually 
believed  to  originate  in  rows  of  cells,  the  cavities  of  which  have  run 
together  by  the  obliteration  of  the  transverse  partitions ;  as  the  per- 
sistent nuclei  of  such  cells  may  be  occasionally  brought  into  view  in 
the  walls  of  the  capillaries.  And  the  same  appears  to  be  the  origin 
of  the  tubular  fibres  of  Muscular  and  Nervous  tissue,  which  contain 
the  elements  characteristic  of  those  tissues;  these  elements, — the 
fibrillae  of  muscle,  and  the  granular  pith  of  the  nerve-tube, — being 
evidently  the  secondary  products  of  parent-cells,  which  seem  to  remain 
as  their  investing  tubuli,  in  the  walls  of  which  the  original  nuclei  are 
often  to  be  seen  (§§  338  and  388). 

258.  Besides  these  changes,  the  original  cells  may  often  undergo 
marked  alterations  of  form;  and  this  quite  independently  of  any  pres- 
sure to  which  they  may  be  subject.  Thus  the  pigment-cells,  as 
already  mentioned  (§  229,)  frequently  exhibit  a  curious  stellate  form; 
arising  from  the  development  of  radiating  prolongations,  which  are 
put  forth  from  the  original  spheroid.  A  form  which  is  frequently 
assumed  by  the  cells  that  are  developed  in  fibrinous  or  plastic  exu- 
dations, and  which  is  also  met  with  in  the  cells  of  tumours,  both 


164 


FUSIFORM  CELLS.—ADIPOSE  TISSUE. 


malignant  (or  Cancerous)  and  non-malignant,  is  that  which  has  re- 
ceived the  designation  oi fusiform  or  spindle-like,  from  its  prolonged 
shape  and  pointed  extremities.  The  various  stages  of  transition, 
which  may  be  observed  between  the  simple  rounded  cell  and  the 
fusiform  cell,  are  shown  in  Fig.  33 ;  and  it  is  there  seen  that,  when 
the  transformation  has  gone  to  its  utmost  extent,  the  nucleus  of  the 
cell  is  no  longer  visible,  so  that  it  bears  a  close  resemblance  to  a 
simple  fibre.  Such  cells  are  found  amongst  the  simple  fibrous  tissues ; 
and,  in  the  opinion  of  many,  they  give  origin  to  them. — The  appear- 
ance of  tissue,  composed  of  fusiform  cells,  is  shown  in  Fig.  34;  this  is 
seldom  met  with  as  a  permanent  part  of  the  normal  fabric  ;  but  it  is  a 
frequent  product  of  morbid  action. 


Fig.  33. 


Fig.  35. 


Fusiform  tissue  of  plastic 
exudations;  o,  fusiform  bo- 
dies without  nuclei ;  b,  nu- 
cleated fusiform  cells ;  c, 
granular  intercellular  sub- 
stance. 


Areolar  and  Adipose  tissue  ; 
a,  a,  fat-cells;  6,  6,  fibres  of  are- 


Transition  from  cellular  to 
fusiform  tissue ;  a,  circular  or 
oval  cells;  6,  the  siime  becoming 
pointed;  c,  fusiform  cells  con- 
taining nuclei ;  rf,  fusiform  cells 
more  elongated,  and  destitute 
of  nuclei. 

259.  We  now  proceed  with  the  description  of  the  various  tissues 
in  the  Human  body,  which  are  composed  of  cells  united  or  trans- 
formed in  the  foregoing  manner ;  and  we  shall  commence  with  Adipose 
or  Fatty  tissue,  which  may  be  considered  as  a  sort  of  link,  connect- 
ing the  permanent  tissues  with  those  which  are  more  actively  con- 
cerned in  the  processes  of  Nutrition,  Secretion,  &c.  The  Adipose 
tissue  is  composed  of  isolated  cells,  which  have  the  power  of  appro- 
priating fatty  matter  from  the  blood,  precisely  in  the  same  manner  as 
the  secreting  cells  appropriate  the  elements  of  bile,  milk,  &c.  These 
cells  are  sometimes  dispersed  in  the  interspaces  of  the  Areolar  tissue ; 
whilst  in  other  cases  they  are  aggregated  in  distinct  masses, — consti- 
tuting the  proper  Adipose  tissue.  In  the  former  case  they  are  held  in 
their  places  by  fibres,  that  traverse  the  areolae  in  different  directions ; 
whilst  in  the  latter,  each  small  cluster  of  fat  cells  is  included  in  a 
common  envelop,  on  the  exterior  of  which  the  blood-vessels  ramify; 
and  these  sacculi  are  held  together  by  areolar  tissue.  We  are  thus 
probably  to  regard  each  fatty  mass  in  the  light  of  a  gland,  or  assem- 


I 


ADIPOSE  TISSUE.  165 

blage  of  secreting  cells,  penetrated  by  blood-vessels,  and  bound 
together  by  fibrous  tissue ;  but  having  its  follicles  closed  instead  of 
open,  (which,  as  just  now  stated,  appears  to  be  the  early  conditions 
of  the  follicles  of  all  glands,  §  251 ;)  and  consequently  retaining  its 
secretion  within  itself,  instead  of  pouring  it  forth  into  a  channel  for 
excretion. 

260.  The  individual  fat-cells  always  present  a  nearly  spherical  or 
spheroidal  form ;  sometimes,  however,  when  they  are  closely  pressed 
together,  they  become  somewhat  polyhedral,  from  the  flattening  of 
their  walls  against  each  other.  Their  intervals  are  traversed  by  a 
minute  network   of  blood-vessels,   from 

which  they  derive  their  secretion ;  and  it  ^^g-  ^^- 

is  probably  by  the  constant  moistening  of 

their  walls  with  a  watery  fluid,  that  their 

contents  are  retained    without   the  least 

transudation,  although  they  are  quite  fluid 

at  the  temperature  of  the  living  body.     If 

the  watery  fluid  of  the  cell- walls  of  a  mass 

of  Fat  be  allowed  to  dry  up,  and  it  be  kept 

at  a    temperature    of   100°,  the    escape    of       Capillary  network  around  Fat-cells. 

the  contained  oily  matter  is  soon  percep- 
tible.— By  this  provision,  the  fatty  matter  is  altogether  prevented 
from  escaping  from  the  cells  of  the  living  tissues,  by  gravitation  or 
pressure  ;  and  as  it  is  not  itself  liable  to  undergo  change  when  secluded 
from  the  air,  it  may  remain  stored  up,  apparently  unaltered,  for  an 
almost  unlimited  period. 

261.  The  consistency,  as  well  as  the  Chemical  constitution,  of  the 
fatty  matter  contained  in  the  Adipose  cells,  varies  in  different  animals, 
according  to  the  relative  proportions  of  three  component  substances, 
which  may  be  distinguished  in  it, — Stearine,  Margarine,  and  Oleine. 
The  two  former  are  solid  when  isolated,  and  the  latter  is  fluid;  but 
at  the  ordinary  temperature  of  the  warm-blooded  animal,  they  are 
dissolved  in  it.  Of  these,  Stearine  is  the  most  solid  ;  and  it  is  most 
largely  present,  therefore,  in  the  hardest  fatty  matter,  such  as  mutton^ 
suet.  It  is  crystaline  like  spermaceti ;  it  is  not  at  all  greasy  between 
the  fingers,  and  it  melts  at  143°.  It  is  insoluble  in  water,  and  in 
cold  alcohol  and  ether ;  but  it  dissolves  in  boiling  alcohol  or  ether, 
crystalizing  as  it  cools.  The  substance  termed  Margarine  exists 
along  with  stearine  in  most  fats;  but  it  is  the  principal  solid  con- 
stituent of  Human  fat,  and  also  of  Olive  oil.  It  corresponds  with 
Stearine  in  many  of  its  properties,  and  is  nearly  allied  to  it  in  Chemi- 
cal composition ;  but  it  is  much  more  soluble  in  alcohol  and  ether, 
and  it  melts  at  118°.  On  the  other  hand,  Oleine^  when  pure,  remains 
fluid  at  the  zero  of  Fahrenheit's  thermometer;  and  it  is  soluble  in 
cold  ether,  from  which  it  can  only  be  separated  by  the  evaporation 
of  the  latter.  It  exists  in  small  quantity  in  the  various  solid  fats  ;  but 
it  constitutes  the  great  mass  of  the  liquid  fixed  oils.  The  tendency 
of  these  to  solidification  by  cold,  depends  upon  the  proportion  of 


166  ADIPOSE  TISSUE. 

stearine  or  margarine  they  may  contain.  All  these  substances  are 
neutral  compounds,  formed  by  the  union  of  Stearic,  Margaric,  and 
Oleic  acids,  respectively,  with  a  base  termed  Glycerine;  this  base  may 
be  obtained  from  any  fatty  matter,  by  treating  it  with  an  alkali,  which 
unites  with  the  acid  and  forms  a  soap,  setting  free  the  Glycerine. 
They  contain  no  Nitrogen  ;  and  their  proportion  of  Oxygen  is  ex- 
tremely small  in  regard  to  their  amount  of  the  Carbon  and  Hydrogen  : 
thus  Stearine  has  142  Carbon  and  141  Hydrogen  to  17  Oxygen ;  and 
in  the  other  substances  the  proportions  are  similar.  The  fatty  bodies 
appear  to  be  mutually  convertible ;  thus  margaric  acid  may  be  pro- 
cured from  stearic  acid,  by  subjecting  it  to  dry  distillation;  and  there 
is  ample  evidence  that  animals  supplied  with  one  of  them  may  pro- 
duce the  others  from  it. 

262.  Since  these  fatty  matters  are  abundantly  supplied  by  the 
Vegetable  kingdom,  and  are  found  to  exist  largely  in  substances  which 
were  not  previously  supposed  to  contain  them,  it  is  not  requisite  to 
suppose,  that  Animals  usually  elaborate  them  by  any  transforming 
process  from  the  elements  of  their  ordinary  food.  The  mode  in  which 
they  are  taken  into  the  blood,  and  the  uses  to  which  they  are  subserv- 
ient, will  be  hereafter  investigated  ;  but  it  may  be  here  remarked, 
that  the  portion  separated  from  the  circulating  fluid  to  form  the  Adi- 
pose tissue,  is  only  that  which  can  be  spared  from  the  other  purposes, 
to  which  the  fatty  matters  have  to  be  applied.  Hence  the  production 
of  this  tissue  depends  in  part  upon  the  amount  of  Fatty  matter  taken 
in  as  food ;  but  this  is  not  entirely  the  case,  as  some  have  main- 
tained ;  for  there  is  sufficient  evidence  that  animals  may  produce  fatty 
matter  by  a  process  of  chemical  transformation,  from  the  starch  or 
sugar  of  their  food,  when  there  is  an  unusual  deficiency  of  it  in  their 
aliment. 

263.  The  development  of  Adipose  tissue  in  the  body  appears  to 
answer  several  distinct  purposes.  It  fills  up  interstices,  and  forms 
a  kind  of  pad  or  cushion  for  the  support  of  movable  parts ;  and  so 
necessary  does  it  seem  for  this  purpose,  that,  even  in  cases  of  great 
emaciation,  some  fat  is  always  found  to  remain,  especially  at  the  base 
of  the  heart  around  the  origin  of  the  great  vessels,  and  in  the  orbit  of 
the  eye.  It  also  assists  in  the  retention  of  the  animal  temperature  by 
its  non-conducting  power ;  and  we  accordingly  find  a  thick  layer  of 
it,  in  those  warm-blooded  mammals  that  inhabit  the  seas, — either 
immediately  beneath  their  skin,  or  incorporated  with  its  substance. 
And  it  also  serves  as  a  reservoir  of  combustible  matter,  at  the  expense 
of  which  the  respiration  may  be  maintained  when  other  materials  are 
deficient;  thus  we  find  that  the  respiration  of  hybernating  animals  is 
kept  up,  during  the  period  when  they  cease  taking  food  (§  121),  by 
the  consumption  of  the  store  of  fat  which  was  laid  up  in  their  bodies, 
previously  to  their  passing  into  that  state;  and  it  is  also  to  be  noticed 
that  herbivorous  animals,  whose  food  is  scanty  during  the  winter, 
usually  exhibit  a  strong  tendency  to  such  an  accumulation,  during  the 
latter  part  of  the  summer,  when  their  food  is  most  rich  and  abundant, 


ADIPOSE  TISSUE.— CARTILAGE.  167 

in  order  to  supply  the  increased  demand  created  by  the  low  external 
temperature  of  the  winter  season.  Other  circumstances  being  the 
same,  it  appears  that  the  length  of  time  during  w^hich  a  warm-blooded 
animal  can  live  without  food,  depends  upon  the  quantity  of  fat  in  its 
body ;  for  the  rapid  low^ering  of  its  temperature,  which  is  the  imme- 
diate cause  of  its  death  (§  117,)  takes  place  as  soon  as  the  whole  of 
this  store  has  been  exhausted.  Of  the  means  by  which  the  fatty 
secretion  is  taken  back  again  into  the  current  of  the  circulation,  when 
it  is  required  for  use  in  the  system,  we  know  nothing  whatever. 

264.  In  the  simpler  forms  of  Cartilage^  we  have  an  example  of  a 
tissue  of  remarkable  permanence,  composed  entirely  of  cells  scattered 
through  an  intercellular  substance.  This  substance  has  a  close 
resemblance  to  Gelatin,  in  composition  and  properties ;  but  is  not 
identical  with  it ;  and  has  received  the  distinguishing  appellation  of 
Chondrine,  which  marks  it  as  the  solidifying  ingredient  of  Cartilage. 
It  requires  longer  boiling  than  Gelatin  for  its  solution  in  water ;  but 
the  solution  fixes  into  a  jelly  in  cooling,  and  dries  by  evaporation  into 
a  glue  that  cannot  be  distinguished  from  that  of  gelatin.  Chondrine 
is  not  precipitated,  however,  by  tannic  acid,  but,  on  the  other  hand, 
it  gives  precipitates  with  acetic  acid,  alum,  acetate  of  lead,  and  proto- 
sulphate  of  iron,  which  do  not  disturb  a  solution  of  gelatin.  That  the 
Chondrine  obtained  by  boiling  cartilage  is  an  actual  component  of 
that  tissue,  and  is  not  a  product  of  the  operation,  appears  from  the 
fact  that  its  elementary  composition  agrees  with  that  of  pure  cartilage, 
when  analyzed  by  combustion.  According  to  Mulder,  the  propor- 
tions of  the  elements  are  as  follows:  32  Carbon,  26  Hydrogen,  4 
Nitrogen,  14  Oxygen ;  with  which  one-tenth  of  an  equivalent  of  sul- 
phur is  combined.  This  formula  is  deduced  from  the  definite  com- 
pound which  Chondrine  forms  w^ith  Chlorine. 

265.  Now  it  is  a  very  curious  fact,  that  all  the  Cartilages  of  the 
foetus, — those  which  are  to  be  converted  into  bone,  as  well  as  those 
which  are  to  remain  unossified, — are  composed  of  Chondrine ;  and 
yet,  as  soon  as  the  process  of  ossification  commences,  the  chondrine 
is  replaced  by  gelatin,  which  is  the  sole  organic  constituent  of  the 
intercellular  substance  of  bones.  The  permanent  cartilages,  however, 
still  contain  only  Chondrine ;  but  if  accidental  bony  deposits  should 
take  place  in  them,  (as  frequently  happens  in  old  persons,  especially 
in  the  cartilages  of  the  ribs,)  the  Chondrine  gives  place  to  Gelatin. 
There  can  be  little  doubt  that,  in  these  cases,  there  is  an  actual  con- 
version of  the  Chondrine  into  Gelatin ;  but  the  mode  in  which  this  is 
effected,  is  not  in  the  least  understood.  As  Chondrine  agrees  more 
nearly  with  Proteine,  in  its  elementary  composition,  than  Gelatin 
does,  it  may  be  surmised  that  it  is  a  sort  of  intermediate  stage  in  the 
conversion  of  Proteine  into  Gelatin  ;  but  it  must  be  kept  in  mind, 
that  no  such  substance  is  met  wdth  in  any  other  of  the  gelatinous 
tissues, — Chondrine  being  restricted  to  pure  cellular  cartilage.  Those 
in  which  the  intercellular  substance  has  the  characters  of  the  white 
fibrous  tissue  (§  189),  yield  gelatin  on  boiling,  in  the  manner  of  the 


168  CARTILAGE. 

ligaments  and  tendons ;  whilst  those  which  contain  much  of  the  yel- 
low or  elastic  tissue,  undergo  very  little  change  by  boiling,  and  only 
yield,  after  several  days,  a  small  quantity  of  an  extract  which  does 
not  form  a  jelly,  but  which  has  the  other  chemical  properties  of 
Chondrine. 

266.  Besides  the  organic  compounds  already  described,  most  Car- 
tilages contain  a  certain  amount  of  mineral  matter,  which  forms  an 
ash  when  they  are  calcined.  This  ash  contains  a  large  proportion  of 
carbonate  and  sulphate  of  soda,  together  with  carbonate  of  lime,  and 
a  small  quantity  of  phosphate  of  lime ;  as  age  advances,  the  propor- 
tion of  the  soluble  compounds  diminishes,  and  the  phosphate  of  lime 
predominates.  This  is  especially  the  case  in  the  costal  cartilages, 
which  almost  invariably  become  converted  into  a  semi-ossified  sub- 
stance, in  old  persons ;  and  it  is  remarkable  that,  even  before  they 
have  themselves  become  thus  condensed,  they  are  united  by  ossific 
matter,  when  they  have  undergone  fracture. 

267.  When  a  pure  Cellular  Cartilage  is  examined  microscopically, 
its  cells  are  seen  to  lie,  sometimes  singly,  and  sometimes  in  clusters 
of  two,  three,  or  four,  in  cavities  excavated  in  the  intercellular  sub- 
stance ;  and  these  occur  at  very  variable  distances.  From  the  various 
appearances  which  may  be  observed  in  the  same  cartilage,  at  different 
stages  of  its  growth,  it  would  appear  that  the  component  cells  multiply 
by  the  doubling  process  already  described  (§  248);  that  they  then 
separate  from  one  another,  each  of  them  drawing  towards  itself  (as  it 
were)  an  envelop  of  intercellular  substance ;  and  that,  by  the  repeti- 
tion of  the  same  process,  the  number  of  cells  in  the  cartilage  may  be 
indefinitely  multiplied.    Various  stages  of  this  history  are  shown  in  the 

accompanying  figure,  which  is 
f''s-37.  taken  from  a  section  of  the 

a  J  cartilaginous  branchial  ray  of 

4^^/^'^^  '"'  ""^  ^      '  ^^^  \?irv3.  or  tadpole  of  the  Rana 

'^-"^^^'  esculenta,  or  Edible  Frog.    In 

the  centre  of  the  figure  are 
shown  three  separate  cells, 
which  have  evidently  been  at 
one  time  in  closer  proximity 
^,  with  each  other.  In  one  of 
ti^  these  cells,  the  nucleus  is  seen 
to  be  developing  two  new  cells 
in  its  interior;  and  a  continua- 
tion of  this  process  would  give 

Section  of  the  Branchial  cartilage  of  Tadpole ;  a,       risC  tO   the    appearance    shown 
group  of  four  cells,  separating  from  each   other;  i,        ^^  J    where  tWO  Cclls  are  shoWn 
pairof  cells  in  apposition;  c,  c,  nuclei  of  cartiluge-cells;        «i.  i^,  y»  nv^i  v.       i  v^  v^w    ^^     a.^ 
rf,  cavity  containing  three  cells.  in     cloSC     COUtact,     being    evi- 

dently the  offspring  of  the  same 
parent.  Now  if  each  of  these  cells  in  like  manner  develops  two 
others  within  itself,  a  cluster  of  four  will  be  developed,  as  shown  at 
a;  and  after  a  time,  intercellular  substance  being  accumulated  around 


I 


CARTI..1GE.  169 

each,  their  walls  will  separate,  and  they  will  acquire  the  character  of 
distinct  cells.  It  would  seem  as  if,  in  other  cases,  one  of  the  first 
pair  of  cells  develops  another  pair  in  its  interior,  whilst  the  other 
(from  some  unknown  cause)  does  not  at  once  proceed  to  do  so;  and 
thus  only  three  cartilage-cells  instead  of  four  are  clustered  together 
in  the  cavity,  as  seen  at  d. 

268.  The  primitive  cellular  organization  now  described  is  retained 
in  some  Cartilages  through  the  whole  duration  of  their  existence. 
This  is  the  case,  for  example,  in  most  of  the  articular  cartilages  of 
joints ;  in  the  cartilaginous  portion  of  the  septum  narium,  in  the  car- 
tilages of  the  alse  and  point  of  the  nose,  in  the  semilunar  cartilages  of 
the  eyelids  ;  in  the  cartilages  of  the  larynx,  (with  the  exception  of  the 
epiglottis,)  the  cartilages  of  the  trachea  and  bronchial  tubes,  the  car- 
tilages of  the  ribs,  and  the  ensiform  cartilage  of  the  sternum.  When 
partial  ossific  deposits  take  place,  it  is  usually  in  the  substance  of 
cellular^  rather  than  in  that  oi fibrous  cartilage. 

269.  When  the  intercellular  substance,  instead  of  being  homo- 
geneous, has  a  fibrous  character,  the  tissue  called  Fihro- Cartilage  is 
produced  ;  and  this  may  be  either  elastic  or  non-elastic,  according  as 
the  yellow  or  the  white  form  of  fibrous  structure  prevails.  In  some 
instances,  the  fibrous  structure  is  so  predominant  over  the  cellular, 
that  the  tissue  has  rather  the  character  of  a  ligament  than  of  a  car- 
tilage. The  white  fibrous  structure  is  seen  in  all  those  cartilages, 
which  unite  the  bones  by  synchondrosis,  and  which  are  destined  not 
merely  to  sustain  pressure,  but  also  to  resist  tension.  This  is  the 
case  especially  in  the  substances,  which  intervene  between  the  verte- 
brae, and  which  connect  the  bones  of  the  pelvis;  these  in  adult  Man 
are  destitute  of  cartilage-corpuscles,  except  in  and  near  their  centres ; 
but  in  the  lower  Vertebrata,  and  in  the  early  condition  of  the  higher, 
the  fibrous  structure  is  confined  to  the  exterior,  and  the  whole  interior 
is  occupied  by  the  ordinary  cartilage-corpuscles.  The  yellow-fibrous 
or  reticulated  structure  is  best  seen  in  the  epiglottis,  and  in  the  concha 
of  the  ear ;  in  the  former  of  these,  scarcely  any  trace  of  cartilage-cor- 
puscles remains ;  and  in  the  latter,  the  cellular  structure  is  only  to  be 
met  w^ith  towards  the  tip. 

270.  We  have  seen  that  the  elements  of  the  cellular  tissues  hitherto 
described,  do  not  come  into  direct  contact  with  the  blood-vessels. 
The  Epidermic  and  Epithelial  cells  are  separated  from  them,  by  the 
continuous  layer  of  basement-membrane,  which  forms  the  surface  of 
the  true  skin,  the  mucous  membranes,  the  glandular  follicles  pro- 
duced from  them,  &c.  &c.  In  like  manner,  the  cells  of  Adipose 
tissue  are  formed  within  membranous  bags ;  on  the  outside  of  which 
the  blood-vessels  form  a  minute  network.  The  cells  of  Cartilage  are 
not  nourished  in  anymore  direct  manner;  and  are  sometimes  at  a 
considerable  distance  from  the  nearest  vessels.  It  is  certain  that  the 
substance  of  the  permanent  cellular  Cartilages  is  not  permeated,  in  a 
state  of  health,  even  by  the  minutest  nutrient  vessels ;  none  such 
being  brought  into  view  under  the  highest  magnifying  power.     They 


170  CELLS  CONNECTED  TOGETHER.—CARTILAGE. 

are,  however,  surrounded  by  vessels,  which  form  large  ampxdlce  or 
varicose  dilatations  at  their  edges,  or  spread  over  their  surfaces ;  and 
it  is  by  the  fluid  which  is  drawn  from  them  by  the  Cartilage-cells, 
that  the  latter  are  nourished.  The  nutrition  of  a  mass  of  Cartilage 
thus  seems  to  bear  a  strong  resemblance  to  that  of  the  thick  fleshy 
Sea-weeds,  which  are  in  like  manner  composed  entirely  of  cells,  with 

Fig.  38. 


Vessels  situated  between  the  attached  synovial  membrane,  and  the  articular  cartilage,  at  the  point 
where  the  ligamemtum  teres  is  inserted  in  the  head  of  the  os  femoris  of  the  human  subject,  between  the 
third  and  fourth  months  of  foetal  life ;— a,  the  surface  of  the  articular  cartilage;  h,  the  vessels  between 
the  articular  cartilage  and  the  synovial  membrane;  c,  the  surface  to  which  the  ligamentum  teres  was 
attached ;  rf,  the  vein ;  e,  the  artery. 

intercellular  substance  disposed  between  them  in  greater  or  smaller 
amount.  The  cells  in  nearest  proximity  to  the  nutrient  fluid,  draw 
from  it  the  requisite  materials,  and  transmit  these  to  the  cells  in  the 
interior  of  the  mass,  receiving  a  fresh  supply  in  their  turn  from  the 
source  in  their  own  neighbourhood.  When  the  Articular  or  other 
cellular  Cartilages  are  inflamed,  however,  we  find  vessels  passing  into 
their  substance;  but  these  vessels  are  formed  in  an  entirely  new  tissue, 
w^hich  is  the  product  of  the  inflammatory  process,  and  cannot  be  said 
to  belong  to  the  Cartilage  itself. 

271.  The  temporary  Cartilages,  which  have  a  like  cellular  struc- 
ture, but  which  are  destined  to  undergo  metamorphosis  into  Bone, 
are  equally  destitute  of  vessels  when  their  mass  is  small ;  but  if  their 
thickness  exceed  an  eighth  of  an  inch,  they  are  permeated  by  canals 
for  the  transmission  of  vessels.  Still  these  vessels  do  not  ramify  with 
any  minuteness  in  the  tissue  ;  and  they  leave  large  islets^  in  which  the 
nutritive  process  must  take  place  on  the  plan  just  described. 

272.  The  Fibro-Cartilages,  formed  as  it  were  by  the  intermingling 
of  two  distinct  elementary  structures,  have  a  degree  of  vascularity 
proportioned  to  the  amount  of  the  fibrous  tissue  which  they  contain  ; 
but  these  vessels  do  not  penetrate  the  cellular  portions,  where  such 
are  distinct  from  the  mixed  structure. 

273.  The  Cartilaginous  tissue  appears  to  be  more  removed  than 
almost  any  other  in  the  body,  from  the  general  tide  of  nutritive  action. 
Its  properties  are  simply  of  a  physical  character;  and  they  are  not 
impaired  for  a  long  time  after  the  death  of  the  tissue,  its  tendency  to 


CORNEA.— CRYSTALINE  LENS. 


ni 


Fig.  39. 


decomposition  being  very  slight,  so  long  as  it  is  exposed  to  ordinary 
temperatures.  It  is  protected  by  its  toughness  and  elasticity  from 
those  mechanical  injuries,  to  which  softer  or  more  brittle  tissues  are 
liable ;  and  consequently  it  has  little  need  of  any  active  power  of 
reparation.  It  seems  doubtful  whether,  when  loss  of  substance  occurs 
as  a  result  of  disease  or  accident,  this  is  repaired  by  real  cartilaginous 
tissue.  In  the  process  of  ulceration,  as  observed  by  Mr.  J.  Goodsir, 
it  appears  that  the  formation  of  depressions  in  the  surface  is  due,  not 
so  much  to  any  change  originating  in  the  substance  of  the  Cartilage, 
as  to  the  eroding  action  of  the  cells  of  the  false  membrane,  which  is 
the  product  of  inflammatory  action  upon  its  surface  ;  and  it  is  in  this 
false  membrane,  that  the  new  vessels  are  formed,  which  dip  down 
into  nipple-like  prolongations  of  the  membrane,  that  enter  corre- 
sponding hollows  excavated  in  the  cartilage. 

274.  The  Cornea  of  the  Eye  bears  a  close  resemblance  to  Cartilage, 
both  in  structure  and  composition  ;  and  it  corresponds  rather  with  the 
cellular  than  with  the  fibrous  form  of  that  tissue.  The  cells  are  not 
so  numerous  as  those  of  the  articular  cartilages ;  and  they  are  sur- 
rounded by  a  plexus  of  bright  fibres,  loosely  connected  together,  so 
as  to  resemble  areolar  tissue.  Two  sets  of  vessels,  a  superficial  and 
a  deep-seated,  surround  the  margin  of 
the  cornea.  The  former  (Fig.  39,  a.) 
belong  rather  to  the  Conjunctival  mem- 
brane, which  forms  the  outer  layer  of  the 
cornea;  and  they  are  prolonged  to  the 
distance  of  one-eighth  or  half  a  line  from 
its  margin,  then  returning  as  veins.  The 
latter  (b)  do  not  pass  into  the  true  Cornea, 
but  terminate  in  dilatations  from  which 
veins  arise,  just  where  it  becomes  con- 
tinuous with  the  sclerotic.  In  diseased 
conditions  of  the  Cornea,  however,  both 
sets  of  vessels  extend  themselves  through 
it.  Notwithstanding  the  absence  of  ves- 
sels in  the  healthy  condition  of  the 
corneal  tissue,  incised  wounds  of  its 
substance  commonly  heal  very  readily, 
as  is  well  seen  after  the  operation  for 
Cataract ;  but  there  is  a  danger  in  carry- 
ing the  incision  around  a  large  propor- 
tion of  its  margin,  lest  the  tissue  should 
be  too  much  cut  off  from  the  supply  of  nutriment  afforded  by  the  am- 
pullae of  the  vessels  that  surround  it. 

275.  The  Crystaline  Lens  of  the  Eye  approaches  Cartilage,  in  its 
structure  and  mode  of  nutrition,  more  nearly  than  any  other  tissue. 
It  may  be  separated  into  numerous  laminse ;  which  are  composed  of 
fibres  that  lock  into  one  another,  by  their  delicately-toothed  margins. 
Each  of  these  fibres  appears  to  be  made  up  of  a  series^of  cells,  linearly 


Nutrient  Vessels  of  the  Cornea  a. 
Superficial  vessels  Deionging  to  me 
Conjunctival  membrane,  and  continued 
over  the  margin  of  tlie  Cornea ;  b.  ves- 
sels of  the  Sclerotic,  returning  at  the 
margin  of  the  Cornea. 


172  CRYSTALINE  AND  VITREOUS  BODIES.— BONE. 

arranged,  which  coalesce  at  an  early  period.  The  lens  is  not  per- 
meated by  blood-vessels ;  at  least  after  it  has  been  completely  formed ; 
these  being  confined  to  the  capsule.  During  the  early  part  of  foetal 
life,  and  in  inflammatory  conditions  of  the  Capsular  membrane,  both 
its  anterior  and  its  posterior  portions  are  distinctly  vascular;  but  at  a 
later  period,  only  the  posterior  half  of  the  Capsule  has  vessels  distri- 
buted upon  its  surface.  It  has  been  shown  by  optical  experiments 
devised  for  the  purpose,  that  a  moderate  vascularity  of  the  posterior 
capsule  does  not  interfere  with  distinct  vision ;  whilst  if  the  anterior 
capsule  were  traversed  by  vessels,  the  picture  on  the  retina  would  be 
no  longer  clear.  The  substance  of  which  the  lens  is  composed  ap- 
pears to  be  soluble  Albumen,  or  perhaps  more  closely  resembles  the 
Globulin  of  the  blood. 

276.  The  Vitreous  body,  which  fills  the  greater  part  of  the  globe  of 
the  eye,  also  seems  to  possess  a  cellular  structure ;  the  cells  contain- 
ing a  fluid,  which  is  little  else  than  water  holding  in  solution  a  small 
quantity  of  albumen  and  saline  matter ;  and  the  membrane  which 
forms  their  walls  being  so  pellucid  as  to  be  scarcely  distinguishable. 
Indeed,  the  cellular  character  of  this  substance  is  chiefly  inferred  from 
the  fact,  that  when  its  capsule  or  enveloping  membrane  is  punctured, 
even  in  several  places,  the  contained  fluid  does  not  speedily  drain 
away, — as  it  would  do  if  it  were  merely  contained  in  the  interstices 
of  an  areolar  tissue.  The  blood-vessels  which  traverse  the  Vitreous 
body  do  not  send  branches  into  its  substance ;  and  it  must  derive  its 
nutriment  from  those  which  are  distributed  minutely  upon  its  general 
envelop,  and  probably  also  from  the  large  plexiform  vessels  of  the 
ciliary  processes  of  the  Choroid  coat. 

277.  We  next  proceed  to  examine  the  nature  of  the  tissues,  which 
have  a  cellular  structure  at  their  original  basis ;  but  which  have 
undergone  a  metamorphosis  in  regard  to  the  arrangement  of  their  ele- 
mentary parts ;  and  which  have  received  an  additional  consolidation, 
by  the  deposition  of  earthy  matter  in  their  substance.  These  tissues 
are  the  Osseous  and  the  Dental, — Bones  and  Teeth.  The  structure 
of  both  of  them  is  well  adapted  to  demonstrate  the  distinction  between 
the  tissues  themselves,  and  those  subsidiary  parts,  by  which  they  are 
connected  with  the  rest  of  the  structure.  We  have  seen  that  Car- 
tilage is  essentially  no7i-vascular ;  that  is,  even  when  it  exists  in  a 
considerable  mass,  it  is  not  traversed  by  vessels,  but  is  nourished  by 
absorption  from  the  fluids  contained  in  the  vessels  distributed  on  its 
exterior.  Now  every  mass  of  Bone  is  penetrated  by  vessels;  never- 
theless these  do  not  penetrate  its  ultimate  substance,  and  may  be 
easily  separated  from  it,  leaving  the  bone  itself  as  it  was.  In  fact,  as 
Mr.  J.  Goodsir  observes,  "  a  well  macerated  bone  is  one  of  the  most 
easily  made,  and,  at  the  same  time  one  of  the  most  curious  anatomical 
preparations.  It  is  a  perfect  example  of  a  texture  completely  isolated ; 
the  vessels,  nerves,  membranes,  and  fat,  are  all  separated,  and  nothing 
is  left  but  the  non-vascular  osseous  substance."  Precisely  the  same 
may  be  said  of  the  substance  of  a  Tooth,  from  which  the  vascular 


STRUCTURE  OF  BONE.  173 

lining  of  the  pulp-cavity  has  been  removed ;  for  it  then  possesses 
neither  vessels,  nerves,  nor  lymphatics  ;  and  yet,  as  we  shall  presently 
see,  it  has  a  highly-organized  structure,  peculiar  to  itself. 

278.  The  general  characters  of  Osseous  texture  vary  according  to 
the  shape  of  the  Bone,  and  the  part  of  it  examined.  Thus  in  the  long 
bones,  we  find  the  shaft  pierced  by  a  central  canal,  which  runs  con- 
tinuously from  one  extremity  to  the  other ;  and  the  hollow  cylinder 
which  surrounds  this  is  very  compact  in  its  structure.  On  the  other 
hand,  the  dilated  ends  of  the  bone  are  not  pene- 
trated by  the  large  central  canal ;  nor  are  they  ^!Ls^ 
composed  of  solid  osseous  substance.  They  are 
made  up  of  cancellated  structure,  as  it  is  termed  ; 
that  is,  of  osseous  lamellae  arid  fibres  interwoven 
together  (like  those  of  areolar  tissue,  on  a  larger 
scale)  so  as  to  form  a  multitude  of  minute  cham- 
bers or  cancelli,  freely  communicating  with  each 
other,  and  with  the  cavity  of  the  shaft;  whilst  the 
whole  is  capped  with  a  thin  layer  of  solid  bone. 
Again,  in  the  thin  flat  bones,  as  the  scapula,  we 
find  the  two  surfaces  composed  of  solid  osseous 
texture,  with  more  or  less  of  cancellated  structure  Extremity  of  os  fe- 
interposed  between  the  layers.  And  in  the  thicker  ["oris,  showing^ancei- 
flat  bones,  as  the  parietal,  frontal,  &c.,  this  can-  layer  ofbone,  in  contact 
cellated  structure  becomes  very  distinct,  and  tTiageJ^6%ancdir  ^^^' 
forms  the   diploe ;   this,  however,  is   sometimes 

deficient,  leaving  a  cavity  analogous  to  the  canal  of  the  long  bones ; 
whilst  the  plates  which  form  the  surfaces  of  the  bone  (the  external 
and  internal  tables  of  the  skull),  resemble  in  their  thickness  and  soli- 
dity, as  well  as  in  the  intimate  structure  presently  to  be  described, 
the  shaft  or  hollow  cylinder  of  those  bones.  Finally,  we  frequently 
.  meet  (especially  in  the  Ethmoid  and  Sphenoid  bones),  with  thin 
lamellae  of  osseous  substance,  resembling  those  which  elsewhere  form 
the  boundaries  of  the  cancelli ;  these  consist  of  but  one  layer  of  bony 
matter,  and  show  none  of  the  varieties  previously  adverted  to ;  they 
are  not  penetrated  by  vessels,  but  are  nourished  only  by  their  sur- 
faces ;  and  they  consequently  exhibit  to  us  the  elements  of  the  osseous 
structure  in  their  simplest  form.  It  will  be  desirable,  therefore,  to 
commence  with  the  description  of  these. 

279.  When  a  thin  natural  lamella  of  this  kind  is  examined,  it  is 
found  to  be  chiefly  made  up  of  a  substance  which  is  apparently  homo- 
geneous, but  which  may  be  seen  (especially  after  prolonged  boiling) 
to  consist  of  minute  granules,  varying  in  size  from  l-6000th  to 
l-14000th  of  an  inch ;  these  are  more  or  less  angular  in  shape,  and 
seem  to  cohere  by  the  medium  of  some  second  substance,  which  is 
dissolved  by  the  boiling.  They  are  composed  of  Calcareous  salts, 
apparently  in  chemical  union  with  the  Gelatin  that  forms  the  basis  of 
the  osseous  substance.  In  the  midst  of  this  granular  substance  a 
number  of  dark  spots  are  to  be  observed,  the  form  of  which  is  very 


174 


STRUCTURE  OF  BONE. 


peculiar.  In  their  general  outline  they  are  usually  somewhat  oval; 
but  they  send  forth  numerous  radiating  prolongations  of  extreme 
minuteness,  which  may  be  frequently  traced  to  a  considerable  dis- 
tance. These  spots,  known  as  the  osseous  corpuscles,  (sometimes 
termed  the  Purkinjean  corpuscles,  after  the  name  of  their  discoverer,) 
are  highly  characteristic  of  the  true  bony  structure,  being  never 
deficient  in  the  minutest  parts  of  the  bones  of  the  higher  animals, 
although  those  of  Fishes  are  frequently  destitute  of  them.     These 

corpuscles    were    formerly    sup- 
^'^-  ^^-  posed,  from  their  dark  appearance, 

to  be  opaque,  and  to  consist  of  ag- 
gregations of  calcareous  matter 
which  would  not  transmit  the 
light:  but  it  is  now  quite  certain, 
that  they  are  lacunce  or  open 
spaces ;  and  that  the  radiating  pro- 
longations from  them,  which  are 
far  smaller  than  the  minutest  capil- 
lary vessel,  are  canaliculi  or  deli- 
cate tubes.  Of  these  canaliculi,  some  may  be  seen  to  interlace  freely 
with  each  other,  whilst  others  proceed  towards  the  surface  of  the 
bony  lamella ;  and  thus  a  system  of  passages,  not  by  any  means  wide 
enough  to  admit  the  blood-corpuscles,  but  capable  of  transmitting  the 
fluid  elements  of  the  blood,  or  matters  selected  from  them,  is  estab- 
lished through  the  whole  substance  of  the  lamella.  The  lacunae  have 
an  average  length  of  1- 1800th  of  an  inch  ;  and  they  are  usually  about 
half  as  wide,  and  one-third  as  thick.     The  diameter  of  the  canaliculi 


Lacunae  of  Osseous  substance,  magnified  500 
diameters ;— a, central  cavity;  b,  its  ramifications. 


is  from  l-12000th  to  l-20000th  of  an  inch. 


Fis.  42. 


Section  of  the  bony  scale  of  Lepidosteus;— a,  showing  the 
regular  distribution  of  the  lacunse  and  of  the  connecting  canali- 
culi ;  b,  small  portion  more  highly  magnified. 


The  succeeding  figure 
represents  the  arrange- 
ment of  these  lacunae  and 
canaliculi  in  the  bony 
scale  of  a  Fish  (the  Lepi- 
dosteus) ;  which  is  al- 
most the  only  existing 
representative  of  a  large 
class  of  bony-scaled 
Fishes,  that  formerly 
tenanted  the  seas.  This 
subject  is  selected  on 
account  of  the  peculiar 
distinctness  with  which 


these  elementary  parts  are  shown ;  and  the  entire  absence  of  any  of 
that  more  complex  arrangement,  caused  by  the  penetration  of  blood- 
vessels, which  we  shall  presently  have  to  describe. 

280.  The  lacunae  of  the  solid  osseous  texture  are  not  unoccupied, 
however,  in  the  living  Bone.  They  are  filled  with  a  minute  granular 
substance ;  which  is  probably  to  be  regarded  (as  first  pointed  out  by 
Mr.  J.  Goodsir)  in  the  light  of  a  germinal  spot  or  nutritive  centre, 


STRUCTURE  OF  BONE.  175 

that  has  the  power  of  drawing  to  itself,  through  its  own  system  of 
canaliculi,  the  nutritive  materials  supplied  by  the  blood-vessels  on 
the  nearest  surface,  and  of  diffusing  these  through  the  surrounding 
substance.  Between  the  blood-vessels  and  the  surface  of  the  bony 
lamella,  however,  there  is  a  layer  of  cells ;  which  are  probably  the 
immediate  agents  in  the  selection  and  elaboration  of  the  nutritive 
matter,  and  which  then  deliver  it  to  betaken  up  by  the  canaliculi. — 
Thus  the  nutrition  of  the  ultimate  osseous  texture  is  carried  on  upon 
the  same  plan  with  that  of  Cartilage ;  being  effected  by  the  imbibition 
of  nutrient  matter  from  the  surface,  through  the  agency  of  cells.  But 
it  differs  in  this ; — that  there  is  a  provision  in  Bone  for  the  ready 
transmission  of  nutrient  matter  through  its  texture,  by  means  of  minute 
channels,  which  does  not  exist  in  Cartilage ; — a  difference  obviously 
required  by  the  greater  solidity  of  the  substance  of  the  former,  which 
does  not  allow  of  the  diffused  imbibition,  that  is  permitted  by  the 
softer  and  moister  nature  of  the  latter.  We  shall  presently  find  that 
they  are  only  formed  at  a  late  stage  of  the  development  of  bone,  when 
the  remaining  tissue  has  acquired  its  completest  consolidation. 

281.  Now,  as  already  remarked,  the  simple  structure  just  described 
is  found,  not  merely  in  the  delicate  plates  which  form  the  thinnest 
part  of  certain  bones  in  Man ;  but  also  in  those  lamellae,  which  form 
the  walls  of  the  cancelli  of  the  larger  and  thicker  bones.  Every  one 
of  these  lamellae  repeats,  in  fact,  the  same  history.  The  cancelli  are 
lined  by  a  membrane  derived  from  that  of  the  cavity  of  the  shaft, 
over  which  blood-vessels  are  minutely  distributed ;  between  these 
blood-vessels  and  the  osseous  texture,  is  a  layer  of  cells ;  and  from 
the  materials  selected  and  communicated  by  these,  each  lamella  is 
nourished,  through  its  system  of  radiating  canaliculi  and  nutritive 
centres.  The  cancelli,  at  the  time  of  their  formation  in  the  f<Btal 
bone,  are  entirely  filled  with  such  cells ;  which  appear  (as  will  be 
presently  explained)  to  be  the  descendants  of  the  cells  of  the  original 
cartilage  ;  but  in  the  adult  bone,  a  large  proportion  of  them  is  filled 
with  fatty  matter,  which  they  secrete  into  their  cavities. — The  vessels 
of  the  cancellated  structure  at  the  extremities  of  the  long  bones,  are 
derived  from  those  of  the  medullary  cavity,  which  is  penetrated  by 
large  trunks  from  the  exterior ;  and  in  the  flat  bones,  they  form  a 
system  of  their  own,  connected  with  the  vessels  of  the  exterior  by 
several  smaller  trunks. 

282.  The  solid  osseous  texture,  which  forms  the  cylindrical  shafts 
of  the  long  bones,  and  the  thick  external  plates  of  the  denser  flat 
bones,  is  not  cut  off  from  nutritive  action  in  the  degree  in  which  it 
might  seem  to  be ;  for  it  is  penetrated  by  a  series  of  large  canals, 
termed  the  Haversian,  (after  Clopton  Havers,  their  discoverer,) 
which  form  a  network  in  its  interior,  and  which  serve  for  the  trans- 
mission of  blood-vessels  into  its  substance.  These  canals,  in  the  long 
bones,  run  for  the  most  part  in  a  direction  parallel  to  the  central 
cavity ;  and  they  communicate  with  this,  with  the  external  surface, 
with  the   cancelli,   and   with   each   other,   by  frequent  transverse 


176 


STRUCTURE  OF  BONE. 


Fig.  43. 


branches ;  so  that  the  whole  system  forms  an  irregular  network,  per- 
vading every  part  of  the  solid  texture,  and  adapted  for  the  establish- 
ment of  vascular  communications  through- 
out. The  diameter  of  the  Haversian  canals 
varies  from  l-2500th  to  l-200th  of  an  inch, 
or  more :  the  smallest  being  only  of  sufficient 
size#o  admit  the  passage  of  a  single  capil- 
lary vessel ;  whilst  the  largest  receives  a 
plexus  of  minute  blood-vessels.  Their  ave- 
rage diameter  maybe  stated  at  about  l-500th 
of  an  inch.  They  are  lined  by  a  membrane, 
which  is  continuous  with  that  of  the  external 
surface,  and  which  carries  this  inwards  (so 
to  speak)  to  form  the  lining  membrane  of  the 
central  cavity,  and  of  the  cancelli.  On  this 
membrane,  a  plexus  of  blood-vessels  is  dis- 
tributed, where  the  size  of  the  canal  admits 
it; — otherwise,  the  tube  encloses  a  single 
twig  of  an  artery  or  vein.  Thus  we  may 
consider  the  whole  Osseous  texture  as  in- 
closed in  a  membranous  bag;  on  which 
blood-vessels  are  minutely  distributed ;  and 
which  is  so  carried  into  the  bone  by  invo- 
lutions and  prolongations,  that  no  part  of 
the  latter  is  ever  far  removed  from  a  vascu- 
lar surface. 

283.  Between  the  vascular  lining  of  the  Haversian  canals,  and 
their  bony  walls,  there  is  a  layer  of  cells  ;  as  in  the  corresponding 
situation  in  the  cancelli :  so  that  it  may  be  stated  as  a  general  fact, 
that  these  everywhere  intervene  between  the  blood-vessels  and  the 
osseous  substance.  In  the  adult  bone,  the  cells  which  fill  the  remain- 
ing cavity  of  these  canals  secrete  fatty  matter ;  this  is  particularly 
evident  in  the  case  of  the  central  cavity,  where  they  constitute  the 
medulla  or  marrow.  It  does  not  appear  that  these  take  any  active 
part  in  the  nutrition  of  the  bone  ;  indeed  in  the  bones  of  Birds,  the 
shaft  is  entirely  hollow,  and  air  is  admitted  into  it  from  the  lungs,  so 
that  its  lining  membrane  is  rendered  subservient  to  the  aeration  of 
the  blood. 

284.  The  arrangement  of  the  elementary  parts  of  the  osseous  sub- 
stance around  the  Haversian  canals,  is  very  interesting  and  beautiful. 
When  a  transverse  section  of  a  long  bone  is  made,  the  open  orifices 
of  the  longitudinal  canals  present  themselves  at  intervals,  sometimes 
connected  by  a  transverse  canal,  where  the  section  happens  to  traverse 
this.  Around  these  orifices,  we  see  the  osseous  matter  arranged  in 
the  form  of  cylinders,  which  appears  to  be  marked  by  concentric 
circles.  Now  when  one  of  these  circles  is  minutely  examined,  it  is 
found  to  be  made  up  of  a  series  of  lacunae,  analogous  to  those  already 
described ;  these,  however,  are  seldom  or  never  so  continuous  as  to 


Haversian  Canal,  seen  on  a 
longitudinal  section  of  the  com- 
pact lissue  of  the  shaft  of  one  of 
the  long  bones ;  1,  arterial  canal ; 
2,  venous  canal ;  3,  dilatation  of 
another  venous  canal. 


1 


STRUCTURE  OF  BONE. 


177 


form  a  complete  circle.  The  long  sides  of  the  lacunse  are  directed, 
the  one  towards  the  Haversian  canal  in  the  centre,  the  other  towards 
the  circular  row  next  beyond  it.  And  when  the  course  of  the  cana- 
liculi  is  traced,  it  is  found  that  these  converge  on  the  inner  side 
towards  the  central  canal,  inosculating  with  those  of  the  series  next 
within,  whilst  those  of  the  outer  side  pass  outwards  in  a  radiating  or 
diverging  direction,  to  inosculate  with  those  of  the  series  next  ex- 
ternal. Thus  a  complete  communication  is  formed,  by  means  of  this 
system  of  radiating  canaliculi,  and  intervening  lacunse,  between  the 
central  canal,  and  the  outermost  cylindrical  lamella  of  bony  matter ; 
and  each  of  these  lamellae  derives  its  nourishment  from  the  vessels  of 
the  central  canal,  through  the  lamellse  which  intervene  between  itself 
and  the  vascular  membrane  lining  that  tube. 

285.  Thus  every  one  of  the  Haversian  canals  is  the  centre  of  a 
cylindrical  ossicle;  which  is  complete  in  itself,  as  far  as  its  elementary 
structure  is  concerned  ;  and  which  has  no  dependence  on,  or  con- 
nection w^ith,  other  similar  ossicles.  These  are  arranged,  however, 
side  by  side,  like  sticks  in  a  faggot ;  they  are  bound  together  by  a 
thin  cylinder  of  bone,  on  the  exterior  of  all,  \vhich  derives  its  nourish- 
ment from  the  periosteum  or  enveloping  membrane;  in  like  manner, 
the  hollow  bundle  is  lined  by  a  similar  cylinder,  which  surrounds  the 
great  medullary  cavity,  and  is  nourished  by  its  vascular  membrane; 
and  the  spaces  that  here  and  there  intervene  between  the  ossicles,  are 
filled  up  with  lamina?,  which  are  parallel  to  those  of  the  external  and 
internal  cylinders,  and  which  seem  to  derive  their  nutriment  from 
them  (Fig.  44,  4).     In  this  manner,  the  whole  structure  acquires  great 


Fig.  44. 


Minute  structure  of  bone,  dra\ii)n  with 
tlie  microscope  from  nature.  Magnified 
800  diameters.  1.  One  of  the  Haversian 
canals  surrounded  by  its  concentric  la- 
meilee.  The  corpuscles  are  seen  between 
the  lamella} ;  but  the  calcigerous  tubuli  are 
omitted.  2.  An  Haversian  canal  with  its 
concentric  lamella?,  Purkinjean  corpuscles 
and  tubuli.  3.  The  area  of  one  of  the 
canals.  4,  4.  Direction  of  the  lamellae  of 
the  great  medullary  canal.  Between  the 
lamellaj  at  the  upper  part  of  the  figure, 
several  very  long  corpuscles  with  their 
tubuli  are  seen.  In  the  lower  part  of  the 
figure,  the  outlines  of  three  olher  canals  are 
given,  in  order  to  show  their  form  and  mode 
of  arrangement  in  the  entire  bone. 


density  and  solidity. — The  structure  of  the  outer  and  inner  tables  of 
the  skull,  and  of  other  thick  solid  layers  of  bone,  is  precisely  similar; 
1.* 


nS  STRUCTURE  AND  COMPOSITION  OF  BONE. 

except  that  the  Haversian  canals  have  no  such  definite  directions,  and 
form  an  irregular  network. 

286.  Thus  we  see  that  each  of  the  lamellae  of  bone,  surrounding  an 
Haversian  canal,  or  bounding  the  cancelli,  may  be  regarded  as  a 
repetition  of  the  simple  bony  plate,  which  draws  its  nourishment 
direct  from  the  vascular  membrane  covering  its  surface,  by  means 
of  its  system  of  lacunae  and  canaliculi.  The  membrane  lining  the 
Haversian  canals,  cancelli,  and  central  medullary  cavity,  is  an  internal 
prolongation  of  that  which  clothes  the  exterior; — ^just  as  the  mucous 
membranes,  with  their  extensions  into  glandular  structures,  are  in- 
ternal prolongations  of  the  true  skin.  Every  Haversian  canal  and 
every  cancellus  are  repetitions  of  each  other  in  all  essential  particulars ; 
their  form  alone  being  different.  The  central  medullary  canal  is  but 
an  enlarged  Haversian  canal  or  cancellus.  And  the  whole  cylin- 
drical shaft  is  a  collection  of  ossicles,  each  of  which  is  a  miniature 
representation  of  itself,  being  a  hollow  cylinder,  with  a  central  vas- 
cular cavity. 

287.  The  principal  features  of  the  Chemical  constitution  of  bone 
are  easily  made   evident.     After  all  the  accessory  parts  have  been 
removed,  and  nothing  remains  but  the  real  osseous  texture,  this  may 
be  separated,  by  simple  processes,  into  its  two  grand  constituents, — 
the   animal  basis,  and  the  calcareous  matter.     The   latter  may  be 
entirely  dissolved  away,  by  maceration  of  the  bone  in  dilute  Muriatic 
or  Nitric  acid  ;  and  a  substance  of  cartilaginous  appearance  is  then 
left,  which,  when  submitted  to  the  action  of  boiling  water  for  a  short 
time,  is  almost  entirely  dissolved  away,  and  the  solution  forms  a  dense 
jelly  on  cooling.     The  same  substance,  Gelatin,  may  be  obtained  by 
long  boiling  under  pressure,  from  previously  unaltered  bone  ;  and  the 
calcareous  matter  is  then  left  in  a  friable  condition.     By  submitting  a 
bone  to  a  heat  sufficient  to  decompose  the  animal  matter,  without 
dissipating  any  of  the   earthy  particles,  we  may  obtain  the  whole 
calcareous  matter  in  situ;  but  the  slightest  violence  is  sufficient  to 
disintegrate  it.     The  bones  of  persons  long  buried  are  often  found  in 
this  condition;  their  form  and  position  being  retained,  until  they  are 
exposed  to  the  air,  or  are  a  little  shaken  ;  when  they  crumble  to  dust. 
— The  proportion  of  the  earthy  matter  of  Bones  to  the  animal  basis 
may  be  differently  stated  ;  according  as  we  include  in  our  estimate  of 
the  latter,  the  contents  of  the  medullary  cavity,  the  Haversian  canals, 
and  the  cancelli ;  or  confine  ourselves  to  that  portion  only  of  the  ani- 
.mal  matter,  which  is  united  with  the  calcareous  element  in  the  proper 
-osseous  tissue.     According  to  the  recent  experiments  of  Dr.  Stark,* 
the   relative   amount  of  the   two  elements,  in  the  latter  estimate,  is 
subject  to  very  little  variation,  either  in  the  different  classes  of  ani- 
mals, or  in  the  same  species   at  different  ages;   the  animal   matter 
composing  about  one-third,  or  33J  per  cent. ;  and  the  mineral  matter 
two-thirds,  or  66|  per  cent.     The  degree  of  hardness  of  bone  does 

♦  Edinburgh  Medical  and  Surgical  Journal,  April,  1845. 


COMPOSITION  OP  BONE.  179 

not  altogether  depend,  therefore,  on  the  amount  of  earthy  matter  they 
may  contain ;  for  the  flexible,  semi-transparent,  easily-divided  bones 
of  Fish  contain  as  large  an  amount  of  animal  matter,  as  the  ivory-like 
leg-bones  of  the  deer  or  sheep.  The  usual  analyses  of  Bone,  how- 
ever, have  been  made  upon  the  former  kind  of  estimate;  and  they 
show  that  the  proportion  of  the  earthy  matter  to  the  whole  of  the 
animal  substance  contained  in  bone,  varies  much  in  different  animals, 
in  the  same  animal  at  different  ages,  and  even  in  different  parts  of  the 
same  skeleton.  The  reason  of  this  will  be  apparent,  when  the  history 
of  the  growth  of  Bone  has  been  explained  ;  since  there  is  a  gradual 
filling-up  of  all  the  cavities  at  first  occupied  by  fat-cells,  vessels,  &c., 
which  does  not  cease  with  adult  age,  but  which  continues  during  the 
whole  of  life.  In  this  manner,  the  bones  of  old  persons  acquire  a 
high  degree  of  solidity,  but  they  become  brittle  in  proportion  to  their 
hardness.  From  the  same  cause,  the  more  solid  bones  contain  a 
larger  proportion  of  bone-earth  than  those  of  a  spongy  or  cancellated 
texture ;  the  temporal  bone,  for  example,  containing  63J^  per  cent., 
whilst  the  scapula  possesses  only  54  per  cent.  In  the  former  of 
these  bones,  the  proportion  is  nearly  the  same  as  that  which  exists 
in  pure  osseous  tissue,  the  amount  of  the  remaining  tissues  which  it 
includes  being  very  small,  on  account  of  the  solidity  of  the  bone:  but 
the  latter  contains  in  its  cancelli  a  large  quantity  of  blood-vessels, 
fat-cells,  &c.,  which  swell  the  proportion  of  the  animal  matter  from 
33^  to  46  per  cent. 

288.  The  Lime  of  bones  is,  for  the  most  part,  in  a  state  of  Phos- 
phate, especially  among  the  higher  animals  ;  the  remainder  is  a  Car- 
bonate. In  Human  bones,  the  proportion  of  the  latter  seems  to  be 
about  one-sixth  or  one-seventh  of  the  whole  amount  of  bone-earth. 
In  the  bones  of  the  lower  animals,  however,  the  proportion  of  Car- 
bonate is  greater ;  and  it  is  curious  that  in  callus,  exostosis,  and  other 
irregular  osseous  formations  in  the  higher  animals,  the  proportion  of 
the  Carbonate  should  be  much  greater  than  in  the  sound  bone.  In 
caries,  however,  the  proportion  of  the  Carbonate  is  less  than  usual. 
The  composition  of  the  Phosphate  of  Lime  in  Bones,  is  somewhat 
peculiar;  eight  proportions  of  the  base  being  united  with  three  of  the 
acid.  According  to  Professor  Graham,  it  is  to  be  regarded  as  a  com- 
pound of  two  tribasic  phosphates ;  one  atom  of  the  neutral  phosphate 
(in  which  one  proportional  of  the  acid  is  united  with  two  of  lime  and 
one  of  water),  being  united  with  two  proportionals  of  the  alkaline 
phosphate,  (in  which  one  part  of  acid  is  united  with  three  of  the  base,) 
together  with  an  atom  of  water,  which  is  driven  off  by  calcination. 
Besides  these  components,  some  Chemists  assert  that  a  small  quantity 
of  Fluoride  of  calcium  is  present  in  Bone  ;  but  this  is  rather  doubtful, 
since  it  has  been  shown  by  Dr.  G.  O.  Rees  that  the  solvent  action 
upon  glass,  which  has  been  supposed  to  be  characteristic  of  fluoric 
acid,  may  be  imitated  by  phosphoric  acid  in  combination  with  water, 
which,  if  heated  upon  glass  of  inferior  quality  until  it  volatilizes,  will 
act  upon  it  with  considerable  energy. — Other  saline  matters,  such  as 


180  SKELETONS  OF  INVERTEBRATA. 

phosphate  of  magnesia,  oxides  of  iron  and  manganese,  and  chloride 
of  sodium,  are  found  in  bones  in  small  amount. 

289.  The  purpose  of  Bone  in  the  Animal  economy  is  obviously 
mechanical^  and  that  only ;  its  use  being,  to  afford  support  and  pro- 
tection to  the  softer  textures,  and  to  form  inflexible  levers,  by  the 
action  of  the  muscles  upon  which,  motion  'may  be  given  to  the  dif- 
ferent parts  of  the  fabric.  A  slight  comparison  of  the  characters  and 
offices  of  the  Bones  of  Vertebrated  Animals,  with  the  structures  which 
form  the  solid  skeletons  of  the  lower  classes,  will  afford  many  points 
of  interest ;  and  will  aid  in  the  comprehension  of  the  purpose  of  the 
highly-elaborate  structure  we  have  been  considering.  Commencing 
with  the  Polypifera,  or  Coral-forming  animals,  we  observe  that  their 
strong  axes  or  sheaths  are  destined  only  to  give  support  to  their  softer 
structures,  and  that  the  parts  once  consolidated  undergo  no  subse- 
quent change.  It  was  formerly  imagined,  that  the  stony  Corals  were 
built  up  by  the  animals  which  form  them,  somewhat  in  the  same 
manner  as  a  Bee  constructs  its  cell.  But  it  is  now  fully  demonstrated, 
that  the  calcareous  matter  (which  here  consists  solely  of  the  Carbonate 
of  Lime)  is  deposited  in  the  cells  of  the  living  tissue,  by  a  secreting 
action  of  their  own  ;  and  that  the  most  solid  mass  of  Coral  thus  has 
an  organized  basis,  as  complete  as  that  of  Bone.  The  proportion  of 
earthy  to  animal  matter,  however,  is  so  great  in  the  former  structures, 
that  very  little,  if  any,  nutrient  changes  can  take  place  in  their  tissue, 
when  once  it  has  become  consolidated.  Such  changes  are  not,  how- 
ever, required.  The  substance  thus  developed  by  the  wonderful 
secreting  powers  of  the  lime-secreting  cells,  which  draw  into  them- 
selves the  small  quantity  of  calcareous  matter  dissolved  in  the  sur- 
rounding water,  is  so  little  disposed  to  undergo  change,  that  it  will 
maintain  its  solidity  for  centuries ;  and  even  when  acted  on  by  water 
or  by  heat,  it  does  not  undergo  disintegration,  for  its  calcareous  par- 
ticles arrange  themselves  in  a  new  method,  and  become  converted 
into  a  solid  crystaline  rock.  Such  rocks,  the  product  of  the  meta- 
morphosis of  ancient  coral-formations,  make  up  a  large  proportion  of 
the  external  crust  of  the  earth.  The  solid  stem  or  sheath,  once 
consolidated,  appears  to  undergo  no  further  change  in  the  living 
Coral-structure  ;  for  its  increase  takes  place,  not  by  interstitial  but 
by  superficial  deposit, — that  is,  not  by  the  diffusion  of  new  matter 
through  its  whole  substance,  separating  the  parts  formerly  deposited 
from  each  other,  but  by  the  mere  addition  of  particles  to  its  surface 
and  extremities.  In  this  manner  the  growth  of  a  solid  Coral-structure 
may  go  on  to  an  enormous  extent ;  the  surface  at  which  the  consoli- 
dating action  is  going  on,  being  the  only  part  alive,  that  is  exhibiting 
any  vital  change ;  and  all  the  rest  of  the  mass  being  henceforth  per- 
fectly inert. 

290.  In  the  class  of  Echinodermata,  which  includes  the  Star-fish, 
Sea-Urchin,  &c.,  we  find  the  calcareous  structure  presenting  a  very 
elaborate  organization  ;  as  an  example  of  this,  we  shall  select  the  shell 
of  the  Echinus,  commonly  known  as  the  Sea-Egg.     This  shell  is  made 


SHELL  OF  ECHINODERMATA. 


181 


up  of  a  number  of  plates,  more  or  less  regularly  hexagonal,  and  fitted 
together  so  as  completely  to  enclose  the  animal,  except  at  two  points, 
one  of  which  is  left  open  for  the  mouth,  the  other  for  the  anus.  On 
the  surface  of  these  plates  are  little  tubercles,  for  the  articulation  of 
the  spines,  which  serve  as  instruments  of  defence  and  of  locomotion. 
The  substance  of  the  shell  and  of  the  spines  is  exactly  alike ;  being  a 
sort  of  areolar  tissue,  consolidated  by  the  deposition  of  calcareous 
matter,  and  having  an  innumerable  series  of  interspaces  or  minute 
cancelli,  freely  communicating  with  each  other.  The  arrangement  of 
this  calcareous  network  in  the  spines,  is  most  varied  and  elaborate ; 
and  causes  thin  sections  of  them  to  be  among  the  most  beautiful  of 
all  microscopic  objects.  The  external  and  internal  surface  of  each 
plate,  in  the  shell  of  the  living  Echinus,  is  covered  with  a  membrane, 

Fig.  45. 


oooooooooooapy 
Ooooo       "^"^ 


Portion  of  the  shell  of  the  Echinus,  showing  at  a  the  constituent  plates  with  the  calcified  areolar 
tissue,  of  which  they  are  composed,  at  b. 

from  which  its  nutrition  is  derived ;  this  membrane  dips  down  into 
the  spaces  between  the  adjacent  plates ;  but  it  does  not  penetrate  the 
substance  of  the  plates  themselves,  nor  does  it  transmit  vessels  to  their 
interior.  A  similar  membrane  covers  and  encircles  the  spines;  and 
it  also  connects  these  with  the  shell,  being  continuous  with  the  mem- 
brane that  envelops  the  latter.  Thus  each  plate  and  spine  is  itself 
completely  extra-vascular;  but  it  is  enclosed  in  a  soft  membrane,  which 
furnishes  (whether  by  vessels  or  otherwise,  has  not  yet  been  ascer- 
tained), the  elements  of  its  nutrition. 

*  291.  But  we  do  not  here  find  any  evidence  of  interstitial  growth  ; 
nor  is  there  any  reason  why  such  should  be  required.  For  the  tissue 
of  which  it  is  composed,  although  of  such  extreme  delicacy,  is  of 
great  permanence,  and  does  not  exhibit  the  slightest  tendency  to 
decay,  however  long  it  is  preserved  ;  so  that,  when  once  consolidated, 
it  appears  to  undergo  no  further  change  in  the  living  animal.  The 
growth  of  the  animal,  however,  requires  a  corresponding  enlargement 
of  its  enveloping  shell ;  and  this  is  provided  for  by  the  simple  process 
of  superficial  deposit,  through  the  subdivision  of  the  whole  shell  into 
component  plates.     For  by  the  addition  of  new  matter  at  the  edge  of 


182  SHELLS  OF  MOLLUSCA. 

eachplate^  by  the  consolidation  of  a  portion  of  the  soft  membrane  that 
intervenes  between  the  adjacent  plates,  the  whole  shell  is  enlarged, 
■without  losing  its  globular  form.  At  the  same  time  it  is  strengthened 
in  a  corresponding  degree,  by  the  consolidation  of  the  soft  tissue  at 
the  surface  of  each  plate.  And,  in  like  manner,  the  spines  are  en- 
larged and  lengthened  by  the  progressive  formation  of  new  layers, 
each  on  the  exterior  of  the  preceding ;  so  that  a  transverse  section 
exhibits  a  number  of  concentric  rings,  like  those  of  an  Exogenous 
tree. — Thus  even  in  the  growth  of  this  complex  and  elaborate  struc- 
ture, we  recognize  the  principle  of  superficial  deposit,  which  we  shall 
find  to  be  universal  amongst  the  hard  parts  of  the  Invertebrata ;  not- 
withstanding that,  at  first  sight,  it  would  have  appeared  impossible  to 
provide  on  this  plan  for  the  gradual  enlargement  of  a  globular  shell, 
completely  enclosing  the  animal,  and  therefore  required  to  keep  pace 
with  the  latter  in  its  rate  of  increase. 

292.  Among  the  Mollusca,  we  find  the  body  sometimes  altogether 
destitute  of  solid  organs  of  support,  protection,  or  locomotion, — as  is 
the  case,  for  example,  in  the  Slug;  and  the  movements  are  feeble  and 
the  habits  inert,  the  muscle  having  no  fixed  points  for  their  attach- 
ment, and  acting  without  any  of  the  advantages  of  leverage.  In  other 
cases,  we  find  the  body  more  or  less  completely  protected  by  a  Shell ; 
which  is  suflficiently  large  in  some  instances  to  cover  the  body  com- 
pletely ;  whilst  in  others,  it  affords  only  a  partial  investment.  The 
plan  on  which  this  shell  is  formed,  however,  is  very  different  from 
that  which  has  just  been  described ;  being  much  less  complex.  The 
Univalve  shells,  or  those  formed  in  one  piece,  are  always  of  a  conical 
form ;  the  cone  being  sometimes  simple,  as  in  the  Limpit ;  in  other 
cases  being  spirally  coiled,  as  in  the  Snail.  Now  the  base  of  this 
cone  is  open  ;  and  through  this,  the  animal  can  project  its  movable 
parts.  When  its  increasing  size  requires  additional  accommodation, 
it  is  obvious  that  an  addition  to  the  large  end  of  the  cone  will  increase 
its  diameter  and  its  length  at  the  same  time ;  so  as  to  afford  the  re- 
quired space,  without  any  alteration  in  the  form  or  dimensions  of  the 
older  and  smaller  portions  of  the  cone.  This  last,  indeed,  is  fre- 
quently quitted  by  the  animal,  and  remains  empty ;  being  sometimes 
separated  from  the  latter  portions,  by  one  or  more  partitions  thrown 
across  by  the  animal, — as  is  seen  especially  in  the  Nautilus  and  other 
chambered  shells.  Besides  the  new  matter  added  to  the  mouth  of 
the  shell,  a  thin  layer  is  usually  formed  over  its  whole  interior  sur-* 
face;  so  that  the  lining  of  the  new  part  is  continuous  with  that  of  the 
old. — In  the  Bivalve  shells,  we  trace  this  mode  of  increase  without 
any  difficulty;  especially  in  such  shells  as  that  of  the  Oyster,  in  which 
the  successive  laminae  remain  distinct.  Each  lamina  is  interior  to  the 
preceding,  being  formed  on  the  living  surface  of  the  animal ;  but  it 
also  projects  beyond  it,  so  as  to  enlarge  the  capacity  of  the  shell ;  and 
as  the  separation  of  the  valves  affords  free  exit  to  those  parts  of  the 
animal,  which  are  capable  of  being  projected  beyond  the  shell,  there 
is  obviously  no  need  of  any  other  provision  to  maintain  the  shell  in 


SHELLS  OF  MOLLUSCA. 


183 


its  natural  form. — Thus  in  the  shells  of  the  Mollusca,  increase  takes 
place  at  the  surfaces  and  edges  only. 

293.  The  proportion  of  organic  and  calcareous  matter  in  Shell 
differs  considerably  in  the  various  tribes.  The  former  is  sometimes 
present  in  such  small  amount,  that  it  can  scarcely  be  detected;  and 
the  condition  of  the  calcareous  matter  then  obviously  approaches  that 
of  a  crystaline  deposit.  But  in  other  instances,  the  animal  basis  is 
very  obvious;  remaining  as  a  thick  consistent  membrane,  after  all  the 
calcareous  matter  has  been  dissolved  away  by  an  acid.  This  mem- 
brane is  formed  of  an  aggregation  of  cells  arranged  with  great  regu- 
larity (Fig.  46,  a;)  the  cavities  of  which  are  filled  with  carbonate  of 

Fig.  46.  <* 


Prismatic  cellular  structure  of  shell  of  Pinna;  a,  surface  of  lamina;  fc,  vertical  section. 


lime  in  a  crystaline  state.  The  form  of  the  cells  approaches  the 
hexagonal;  their  diameter  varies  in  different  shells  from  1-lOOth  to 
l-2800th  of  an  inch ;  their  thickness  also  is  extremely  variable,  even 
in  different  parts  of  the  same  shell.  Thus  we  sometimes  meet  with  a 
lamina  of  such  tenuity,  as  not  to  measure  1-lOOth  of  an  inch  in  thick- 
ness; whilst  in  other  instances,  a  single  layer  may  have  a  thickness 
of  half  an  inch,  or  even  (in  certain  large  fossil  species)  of  an  inch  or 
more.  In  this  case,  the  cells,  instead  of  being  thin  flat  scales  like  the 
pavement-epithelium  (§  233),  are  long  prisms,  somewhat  like  the 
cells  of  the  cylinder-epithelium  (Fig.  22),  with  their  walls  flattened 
against  each  other.  The  appearance  which  is  then  presented  by  a 
vertical  section  of  them,  is  represented  in  Fig.  46,  6.  The  long 
prismatic  cells  are  there  seen  to  be  marked  by  delicate  transverse 
striae ;  and  these,  taken  in  connection  with  other  indications,  appear 
to  show,  that  every  such  prism  is  in  reality  formed  by  the  coalescence 
of  a  pile  of  flat  cells,  resembling  those  which  are  seen  in  the  very  thin 
laminae  just  described  ;  so  that  the  thickness  of  the  layer  depends  upon 
the  number  of  the  cellular  lamina?,  which  have  coalesced  to  form  its 
component  prisms.  This  character  is  of  interest,  as  representing  on 
a  magnified  scale  a  corresponding  appearance  in  the  enamel  of  human 


184  SKELETON  OF  ARTICULATA. 

Tooth,  which  we  shall  presently  find  to  be  formed  upon  the  very  same 
plan. 

294.  We  are  to  regard  this  kind  of  shell-substance,  therefore,  as 
formed  by  the  secreting  action  of  the  epithelial-cells  covering  the 
mantle  of  the  animal, — which  membrane,  though  it  answers  in  posi- 
tion to  the  skin,  has  the  soft,  spongy,  glandular  character  of  a  mucous 
membrane.  These  draw  calcareous  matter  into  their  cavities,  as  a 
part  of  their  own  process  of  growth ;  this  matter  being  supplied  from 
the  fluids  of  the  vascular  surface  beneath.  Now  when  these  cal- 
cigerous  cells  are  separated  by  intercellular  substance,  they  remain 
distinct  through  the  whole  of  their  lives,  and  they  form  by  their  cohesion 
a  tenacious  membrane,  that  retains  its  consistency  after  the  removal 
of  the  calcareous  Aatter.  But  this  is  only  the  case  in  certain  groups 
of  shells,  chiefly  belonging  to  the  bivalve  division.  When  the  inter- 
cellular substance  is  wanting,  and  the  cells  come  into  close  contact, 
their  partitions  become  indistinct  on  account  of  their  extreme  tenuity; 
and  not  unfrequently  a  fusion  of  the  whole  substance  appears  to  take 
place,  by  the  dissolution  of  the  original  cell- walls,  so  that  it  becomes 
more  or  less  homogeneous, — traces  of  the  original  cellular  structure 
being  here  and  there  distinguishable  (§  255). 

295.  Sometimes  where  this  fusion  has  taken  place,  so  as  to  oblite- 
rate the  original  cell-structure,  we  find  the  almost  homogeneous  sub- 
stance traversed  by  a  series  of  tubuli,  not  arranged,  however,  in  any 
very  definite   direction,  but  forming  an  irregular  network.     These 

tubes  vary  in  size  from  l-2000th 
^'^^'''  to   l-20,000th   of  an   inch;  but 

their  general  diameter,  in  the 
shells  in  which  they  most  abound, 
is  l-4500th  of  an  inch.  In  the 
larger  tubuli,  something  of  a 
bead-like  structure  may  occa- 
sionally be  seen  ;  as  if  their  in- 
terior were  occupied  by  rounded 
granules  arranged  in  a  linear 
direction.  Although  it  might  be 
supposed  that  this  structure  is 
destined  to  convey  nutrient  fluid  into  the  substance  of  the  shell,  yet 
there  is  no  evidence  that  such  is  the  fact ;  and,  on  the  contrary,  there 
is  ample  evidence,  that,  even  in  shells  most  copiously  traversed  by 
these  tubuli,  no  processes  of  interstitial  growth  or  renewal  take  place. 
The  permanent  character  of  the  substance  of  all  Shells,  when  once  it 
is  fully  formed,  is  as  remarkable  as  that  of  Coral;  and  as  the  adapta- 
tion of  their  size,  to  that  of  the  animals  to  which  they  belong,  is  en- 
tirely eflfected  by  additions  to  their  surfaces  and  edges,  no  interstitial 
deposit  can  have  a  share  in  producing  it. 

296.  Among  the  Articulated  classes,  we  still  find  that  the  skeleton 
as  altogether  external,  and  belongs  therefore  to  the  cutaneous  system  ; 
but  it  is  formed  upon  a  very  different  plan  from  the  shells  of  the  Mol- 


Tubular  shell-structure,  from  Anomia. 


MOULTING.— SHELLS  OF  CRUSTACEA.  185 

lusca,  being  closely  fitted  to  the  body,  and  enveloping  every  part  of 
it ;  consequently  it  must  increase  in  capacity,  with  the  advancing 
growth  of  the  contained  structures.  Moreover  it  is  destined  not 
merely  to  afford  support  and  protection  to  these,  but  to  serve  for  the 
attachment  of  the  muscles  by  which  the  body  and  limbs  are  moved ; 
and  the  hard  envelops  of  the  latter  serve,  like  the  bones  of  the  Verte- 
brata,  as  levers  by  which  the  motor  powers  of  the  muscles  are  more 
advantageously  employed.  Again,  the  hard  envelops  of  the  body  and 
limbs  are  not  formed  of  distinct  plates,  like  those  of  the  Echinus-shell, 
but  are  only  divided  by  sutures  at  the  joints,  for  the  purpose  of  per- 
mitting the  requisite  freedom  of  motion.  It  might  have  been  thought 
that  here,  if  anywhere,  a  process  of  interstitial  growth  would  have 
existed,  to  adapt  the  capacity  of  the  envelops  to  the  dimensions  of 
the  contained  parts,  as  the  latter  increase  with  the  growth  of  the 
animal ;  but,  true  to  the  general  principle,  that  epidermic  structures 
are  not  only  extra-vascular,  but  that  they  undergo  no  change  when 
they  are  once  fully  formed,  we  find  that  the  hard  envelops  of  Articu- 
lated animals  are  thrown  off,  or  exuviated,  when  the  contained  parts 
require  an  increase  of  room ;  and  that  a  new  covering  is  formed  from 
their  surface,  adapted  to  their  enlarged  dimensions. 

297.  This  is  well  known  to  occur  at  certain  intervals  in  Crabs, 
Lobsters,  and  other  Crustacea ;  which  thus  exuviate  not  merely  the 
outer  shell,  with  the  continuation  of  the  epidermis  over  the  eyes,  but 
also  its  internal  reflexion,  which  forms  the  lining  of  the  oesophagus 
and  stomach,  and  the  tendinous  plates  by  which  the  muscles  are 
attached  to  the  lining  of  the  shell.  A  similar  moulting  may  be  ob- 
served to  occur  in  some  of  the  minute  Entomostracous  Crustacea  of 
our  pools,  every  two  or  three  days,  even  after  the  animals  seem  to  be 
full  grown.  During  the  early  growth  of  Insects,  Spiders,  Centipedes, 
&c.,  a  similar  moult  is  frequently  repeated  at  short  intervals  ;  but  after 
these  animals  have  attained  their  full  growth,  which  is  the  case  with 
Insects  at  their  last  change,  no  further  moulting  takes  place,  the 
necessity  for  it  having  ceased. — This  moulting  is  precisely  analogous 
to  the  exfoliation  and  new  formation  of  the  Epidermis,  in  Man  and 
most  other  Vertebrata;  differing  from  it  only  in  this,  that  the  latter  is 
constantly  taking  place  to  a  small  extent,  whilst  the  former  is  com- 
pletely effected  at  certain  intervals,  and  then  ceases.  We  have  ex- 
amples of  a  periodical  complete  moult  in  Vertebrata,  however,  among 
Serpents  and  Frogs. 

298.  The  structure  of  the  hard  envelops  of  Articulated  animals 
corresponds  with  that  of  the  Epidermis  and  its  appendages  in  Man. 
The  firm  casings  of  Beetles,  for  example,  are  formed  of  layers  of 
epidermic  cells,  united  together,  and  having  their  cavities  filled  by  a 
horny  secretion.  The  densest  structure  is  found  in  the  calcareous 
shells  of  the  Crustacea  ;  which  consist  of  a  substance  precisely  analo- 
gous to  the  Dentine  of  Teeth  (§  311);  covered  on  the  exterior  with  a 
layer  of  pigment-cells.  The  calcareous  matter  consist  chiefly  of  car- 
bonate of  lime;  but  traces  of  the  phosphate  are  also  found.     The 


186  BONE  OF  VERTEBRATA. 

animal  basis  has  a  firm  consistent  structure,  resembling  that  of  teeth. 
A  thin  vertical  section  shows  the  tubuli  running  nearly  parallel,  but 
with  occasional  undulations,  from  the  internal  surface  towards  the 
external ;  but  no  traces  of  the  original  calcigerous  cells  can  be  detected 
in  the  fully-formed  shell,  the  process  of  fusion  having  gone  so  far  as 
to  obliterate  them.  The  manner  in  which  these  tubuli  are  formed, 
will  be  presently  considered,  under  the  head  of  Dental  substance. 

299.  Now  the  condition  of  the  osseous  skeleton  of  Vertebrated 
animals  is  altogether  ditFerent.  It  forms  a  part  of  the  internal  sub- 
stance of  their  bodies ;  and  as  these  grow  in  every  part,  and  not 
merely  by  addition  to  this  or  that  portion,  so  must  the  Bones  also, 
in  order  to  keep  pace  with  the  rest  of  the  structure.  Hence  we 
find  them  so  formed,  that  the  processes  of  interstitial  deposition  may 
be  continually  going  on  in  their  fabric,  as  in  that  of  the  softer  tissues  ; 
and  the  changes  in  their  substance  do  not  cease,  even  when  they  have 
acquired  their  full  size.  The  continuance  of  these  changes  appears 
destined,  not  so  much  to  repair  any  waste  occasioned  by  decomposi- 
tion,— for  this  must  be  very  trifling  in  a  tissue  of  such  solidity, — as  to 
keep  the  fabric  in  a  condition,  in  which  it  may  repair  the  injuries  in 
its  substance  occasioned  by  accident  or  disease.  The  degree  of  this 
reparative  power  is  proportional,  as  we  shall  presently  see,  to  the 
activity  of  the  normal  changes,  which  are  continually  taking  place  in 
the  bone  ;  and  is  thus  much  greater  in  youth  than  in  middle  life,  and 
greater  in  the  vigour  of  manhood  than  in  old  age. 

300.  We  shall  commence  the  history  of  the  development  of  Bone, 
with  the  period  in  which  its  condition  resembles  that  of  the  permanent 
Cartilages.  As  already  mentioned,  there  is  no  essential  difference 
between  the  temporary  and  permanent  Cartilages,  in  regard  to  their 
ultimate  structure  ;  the  former,  however,  are  more  commonly  traversed 
by  vessels,  especially  when  their  mass  is  considerable.  These  ves- 
sels, however,  do  not  pass  at  once  from  the  exterior  of  the  cartilage 
into  its  substance ;  but  they  are  conveyed  inwards  along  canals,  which 
are  lined  by  an  extension  of  the  perichondrium  or  investing  mem- 
brane, and  which  may  thus  be  regarded  as  so  many  involutions  of 
the  outer  surface  of  the  cartilage.  These  canals  are  especially  de- 
veloped at  certain  points,  which  are  to  be  the  centres  of  the  ossifying 
process  ;  of  these  puncta  ossificationis,  we  usually  find  one  in  the 
centre  of  the  shaft  of  a  long  bone,  and  one  in  each  of  its  epiphyses ; 
in  the  flat  bones  there  is  one  in  the  middle  of  the  surface,  and  one  in 
each  of  the  principal  processes.  Up  to  a  late  stage  of  the  ossifying 
process,  the  parts  which  contain  distinct  centres  are  not  connected  by 
bony  union,  so  that  they  fall  apart  by  maceration  ;  and  even  when 
they  should  normally  unite,  they  sometimes  remain  separate, — as  in 
the  case  of  the  Frontal  bone,  in  which  we  frequently  meet  with  a 
continuation  of  the  sagittal  suture  down  the  middle,  dividing  it  into 
two  equal  halves,  which  have  originated  in  two  distinct  centres  of 
ossification.  It  is  interesting  to  remark  that,  in  the  two  lowest  classes 
of  Vertebrata, — Fishes  and  Reptiles, — we  find  the  several  parts  of 


CONVERSION  OF  CARTILAGE  INTO  BONE. 


187 


the  osseous  system  presenting,  in  a  permanent  form,  many  of  the 
conditions  which  are  transitory  in  the  higher ;  thus  the  different  por- 
tions of  each  vertebra,  the  body,  lateral  arches,  spinous  and  transverse 
processes,  &c.,  which  have  their  distinct  centres  of  ossification,  but 
which  early  unite  in  Man,  remain  permanently  distinct  in  the  lower 
Fishes  ;  the  division  of  the  frontal  bone,  just  adverted  to,  is  constant 
amongst  Reptiles ;  and  in  that  class  we  meet  with  a  permanent  sepa- 
ration of  the  parts  of  the  occipital  and  temporal  bones,  which,  being 
formed  from  distinct  centres  of  ossification,  are  at  first  distinct  in  the 
higher  animals. 

301.  During  the  formation  of  the  pundum  ossificationis,  and  the 
spread  of  the  vessels  into  the  cartilaginous  matrix,  certain  changes 
are  taking  place  in  the  substance  of  the  latter,  preparatory  to  its  con- 
version into  bone.  Instead  of  single  isolated  cells,  or  groups  of  two, 
three,  or  four,  such  as  w^e  have  seen  to  be  characteristic  of  ordinary 
Cartilage,  (§  267,)  we  find,  as  we  approach  the  ossifying  centre, 
clusters  made  up  of  a  larger  number,  which  appear  to  be  formed  by  a 
continuance  of  the  same 

multiplying  process   as  ^'^s-  4S. 

that  already  described. 
And  when  we  pass  still 
nearer  we  see  that  these 
clusters  are  composed 
of  a  yet  greater  number 
of  cells,  which  are  ar- 
ranged in  long  rows, 
w^hose  direction  corre- 
sponds with  the  longitu- 
dinal axis  of  the  bone  ; 
these  clusters  are  still 
separated  by  intercellu- 
lar substance,  and  it  is 
in  this,  that  the  ossific  matter  is  first  deposited 


Section  of  Cartilage,  near  the  seat  of  ossification;  each  single 
cell  having  given  birth  to  four,  five  or  six  cells,  which  form  clus- 
ters. These  clusters  become  larger  toveards  the  right  of  the 
figure,  and  their  cells  more  numerous  and  larger;  their  long  di- 
ameter being  l-1500th  of  an  inch. 


Thus  if  we  separate 


Fig.  49. 


m^M 
(d 


The  same  cartilage  at  the  seat  of  ossification ;  the  clusters  of  cells  are  arranged  in  columns ;  the  in- 
tercellular spaces  between  the  columns  being  l-3250th  of  an  inch  in  breadth.  To  the  right  of  the  figure, 
osseous  fibres  are  seen  occupying  the  intercellular  spaces  at  first  bounding  the  clusters  laterally,  then 
splitting  them  longitudinally  and  encircling  each  separate  cell.  The  greater  opacity  of  the  right  hand 
border  is  due  to  a  threefold  cause,  the  increase  of  osseous  fibres,  the  opacity  of  the  contents  of  the 
cells,  and  the  multiplication  of  oil-globules. 


188  PRODUCTION  AND  GROWTH  OF  BONE. 

the  cartilaginous  and  the  osseous  substance  at  this  period,  we  find 
that  the  ends  of  the  rows  of  cartilage-cells  are  received  into  deep 
narrow  cups  of  bone,  formed  by  the  transformation  of  the  intercellu- 
lar substance  between  them.  Immediately  upon  the  ossifying  surface, 
the  nuclei,  which  were  before  closely  compressed,  separate  considera- 
bly from  one  another,  by  the  increase  of  material  within  the  cells ;  and 
the  nuclei  themselves  become  larger  and  more  transparent.  These 
changes  constitute  the  first  stage  of  the  process  of  ossification,  which 
extends  only  to  the  calcification  of  the  intercellular  substance ;  in 
this  stage  there  are  no  blood-vessels  directly  concerned.  The  bony 
lamellae  thus  formed,  mark  out  the  boundaries  of  the  cancelli  and 
Haversian  canals ;  which  are  afterwards  to  occupy  a  part  of  the  space 
that  is  hitherto  filled  by  the  rows  of  cartilage-corpuscles. 

302.  The  second  stage  of  the  ossifying  process  consists  in  the  fur- 
ther transformation  of  the  original  cartilage-cells.  These  seem  to  be- 
come flattened  against  the  osseous  layers  already  formed,  and  then  to 
become  themselves  consolidated  by  the  secretion  of  calcareous  mat- 
ter into  their  interior, — at  the  same  time  coalescing  to  such  a  degree, 
that  the  original  boundaries  of  the  cells  can  no  longer  be  traced. 
The  consolidation,  however,  does  not  extend  to  the  nuclei  of  the 
cells ;  which  retain  their  granular  condition,  and,  being  surrounded 
by  calcareous  matter,  are  enclosed  in  cavities  which  take  their  own 
shape.  These  cavities  are  the  subsequent  lacunce  of  the  bony  struc- 
ture ;  and  the  branching  canaliculi  proceeding  from  them  become 
more  and  more  distinct,  as  the  consolidation  of  the  surrounding  struc- 
ture is  completed.  By  the  continuation  of  this  process,  one  layer  of 
cells  after  another  is  converted  into  bony  matter ;  and  the  canals, 
which  at  first  occupied  the  whole  diameter  of  the  cylindrical  ossicles 
shown  in  Fig.  44,  become  gradually  contracted  by  these  deposits  upon 
their  walls.  The  cause  of  the  concentric  lamination  of  the  osseous 
matter  in  each  of  the  ossicles,  of  which  the  permanent  Haversian 
canal  is  the  centre,  is  thus  apparent. 

303.  As  the  calcification  of  the  original  cartilage-cell  goes  on,  a 
new  substance  appears  in  the  cavities  of  the  cancelli  and  canals ; 
this  is  a  cellular  mass  resembling  that  in  which  all  new  tissues  origi- 
nate ;  and  it  seems  to  be  from  this,  that  the  vascular  lining  is  formed, 
which  gradually  extends  itself  into  the  cancelli  and  canals,  and  which 
is  to  become  from  henceforth  the  principal  source  of  the  growth  and 
nutrition  of  Bone.  From  the  central  part  of  this  blastema,  the  fat- 
c6lls,  constituting  the  medulla,  must  be  generated.  But,  as  already 
stated  (§  283),  a  layer  of  cells  resembling  the  originals  constantly 
intervenes  between  the  bony  walls  of  the  canals  and  cancelli,  and 
their  vascular  lining ;  apparently  for  the  purpose  of  serving  as  the 
immediate  agent  in  the  nutrition  of  the  osseous  tissue. 

304.  When  the  complete  Ossification  of  the  temporary  Cartilage 
has  thus  been  effected,  the  Bone  has  still  to  be  enlarged,  in  conformity 
w^ith  the  increasing  size  of  the  surrounding  parts ;  and  this  enlarge- 
ment is  due  in  part  to  superficial^  in  part  to  interstitial  addition.  The 


GROWTH  OF  BONE.  189 

superficial  addition  is  due  to  the  progressive  formation  and  conversion 
of  new  cartilage  at  the  edges  and  surfaces  of  the  bone,  or  at  the  im- 
perfectly-consolidated part  that  intervenes  between  the  separately- 
ossified  portions  of  the  same  bone.  Thus  it  was  long  since  proved  by 
the  experiments  of  Hales  and  Hunter,  that  the  growth  of  a  long  bone 
takes  place  chiefly  towards  the  extremities  ;  for  they  found  that,  when 
metallic  substances  were  inserted  in  the  shaft  of  a  growing  bone  of  a 
young  animal,  the  distance  between  them  was  but  little  altered  after 
a  long  interval,  whilst  space  between  the  extremities  of  the  bone  had 
greatly  increased.  And  it  seems  that,  at  a  later  period,  when  the 
epiphyses  have  become  completely  united  to  the  shaft,  an  elongation 
continues  to  take  place,  by  the  slow  ossification  of  the  articular  carti- 
lage.— Again,  the  bone  is  progressively  increased  in  thickness,  by 
the  gradual  production  of  new  osseous  matter  upon  its  surface ;  this 
production  taking  place  exactly  upon  the  same  plan  with  the  original 
process,  and  involving  the  formation  of  new  Haversian  canals  and 
concentric  lamellae,  so  that  no  distinction  can  be  traced  between  the 
new  and  the  older  layers. 

305.  If  this  were  the  whole  history  of  the  growth  of  Bone,  there 
would  be  no  essential  difference  between  the  character  of  its  nutri- 
tion, and  that  of  the  skeletons  of  the  Invertebrata.  But  it  is  unques- 
tionable, that  bone  is  also  susceptible  of  an  interstitial  change,  though 
this  is  of  a  slow  and  gradual  nature.  The  layers  first  deposited  on 
the  inner  surface  of  the  early  cancelli,  are  pushed  outwards  by  the 
succeeding  ones,  and  gradually  acquire  an  increased  diameter ;  so 
that  the  ultimate  dimensions  of  the  cancelli  and  cylindrical  ossicles 
far  exceed  those  of  the  primitive  cavities  marked  out  by  the  calcifi- 
cation of  the  intercellular  substance  ;  and  this  last,  also,  must  be 
greatly  extended  to  permit  such  an  increase.  This  process  could  not 
go  on  beyond  a  certain  point,  however,  without  removing  the  outer 
laminae  too  far  from  the  vascular  lining  of  the  Haversian  canals  ;  and 
we  consequently  find  that  the  increase  of  the  bone  takes  place  by 
superficial  addition,  wherever  this  is  admissible. — A  very  remarkable 
change  takes  place  in  the  interior  of  the  long  bones  of  young  animals, 
for  the  production  of  the  central  medullary  cavity.  At  an  early  pe- 
riod, no  such  cavity  exists,  and  its  place  is  occupied  by  small  can- 
celli ;  this  is  the  permanent  condition  of  the  bones  in  most  Reptiles. 
The  cancelli  gradually  enlarge,  however;  and  those  within  the  shaft 
coalesce  with  one  another  until  a  continuous  tube  is  formed,  around 
which  the  cancelli  are  large,  open,  and  irregular.  At  the  same  time, 
the  diameter  of  the  surrounding  shaft  is  increasing  by  the  process  of 
interstitial  growth  just  described  ;  so  that  the  size  of  the  medullary 
cavity  at  last  becomes  greater  than  that  of  the  whole  shaft  when  its 
formation  commenced.  The  aggregation  of  the  osseous  matter  in  a 
hollow  cylinder,  instead  of  a  solid  one,  is  the  form  most  favourable 
to  strength,  as  may  be  easily  proved  upon  mechanical  principles.  The 
same  arrangement  is  adopted  in  the  arts,  wherever  it  is  desired  to 
obtain  the  greatest  strength  with  a  limited  amount  of  material. 


190  GROWTH  AND  REGENERATION  OF  BONE. 

306.  The  difference  in  the  relations  of  the  Osseous  substance  to 
the  vascular  network,  at  different  ages, — accounting  for  the  varia- 
tions in  the  rapidity  of  its  nutrition  and  reparation, — is  well  displayed 
in  the  effects  of  Madder.  This  substance  has  a  peculiar  affinity  for 
Phosphate  of  Lime  ;  so  that  when  the  latter  is  formed  by  precipita- 
tion in  a  fluid  tinged  with  madder,  it  attracts  colour  to  it  in  its  de- 
scent, and  falls  to  the  bottom  richly  tinted.  Now  when  animals  are 
fed  with  this  substance,  it  is  found  that  their  bones  become  tinged 
with  it ;  the  period  required  being  in  the  inverse  proportion  to  their 
age.  Thus  in  a  very  young  animal  a  single  day  suffices  to  colour 
the  entire  skeleton,  for  in  them  there  is  no  osseous  matter  far  from 
the  vascular  surfaces  ;  when  sections  are  made,  however,  of  the  bones 
thus  tinged,  it  is  found  that  the  colour  is  confined  to  the  immediate 
neighbourhood  of  the  Haversian  canals,  each  of  which  is  encircled 
by  a  crimson  ring.  In  full-grown  animals,  the  bones  are  very  slowly 
tinged  ;  because  the  osseous  texture  is  much  more  consolidated  and 
less  permeable  to  fluid  than  in  earlier  life  ;  and  because,  owing  to 
the  formation  of  new  concentric  lamellae,  the  outer  and  older  ones 
are  pushed  to  a  greater  distance  from  the  Haversian  canals,  the  di- 
ameter of  which  is  contracted.  In  the  bones  of  half-grown  animals, 
a  part  of  the  bone  is  nearly  in  the  perfect  condition,  while  a  part  is 
new  and  easily  coloured  ;  so  that  the  action  of  this  substance  enables 
us  to  distinguish  the  new  from  the  old. 

307.  The  Regeneration  of  Bone,  after  loss  of  its  substance  by  dis- 
ease or  injury  is  extremely  complete  ;  in  fact  there  is  no  other  struc- 
ture of  so  complex  a  nature,  which  is  capable  of  being  so  thoroughly 
repaired.  Although  the  regenerative  power  appears  to  be  so  much 
less  in  Vertebrated  animals^  than  it  is  in  the  lower  Invertebrata,  yet 
it  is  probably  not  at  all  lower  in  reality, — the  new  structures  actually 
formed  being  as  complex  in  the  one  case  as  in  the  other.  It  is  no- 
where, perhaps,  more  remarkably  manifested,  than  in  the  reformation 
of  nearly  an  entire  bone,  when  the  original  one  has  been  lost  by  dis- 
ease ;  all  the  attachments  of  muscles  and  ligaments,  as  well  as  the 
external  form  and  internal  structure,  being  ultimately  found  as  com- 
plete in  the  new  bone,  as  they  originally  w^ere  in  that  which  it  has 
replaced.  Much  discussion  has  taken  place  in  regard  to  the  degree, 
in  which  the  different  membranous  structures,  that  surround  bone  and 
penetrate  its  substance,  participate  in  its  regeneration  ;  some  having 
supposed  the  periosteum  to  have  the  power  of  itself  ybrmi??^  new 
bone,  others  attributing  the  same  power  to  the  membrane  lining  the 
medullary  cavities.  It  appears  next  to  certain,  however,  that  new 
osseous  tissue  can  only  be  formed  in  continuity  with  that  which  pre- 
viously existed  ;  and  that  it  may  be  generated,  by  the  mediation  of 
even  very  minute  fragments  of  such  tissue,  from  any  of  the  vascular 
membranes  that  happen  to  supply  it.  Thus  when  the  portion  of  the 
shaft  of  a  bone  is  entirely  removed,  but  the  periosteum  is  left,  the 
space  is  filled  up  with  new  bony  matter  in  the  course  of  a  few  weeks; 
though,  if  the  periosteum  be  also  removed,  the  formation  of  new  mat- 


REPARATION  OF  BONE.  191 

ter  will  be  confined  to  a  small  addition  in  a  conical  form  to  the  two 
extremities,  a  large  interspace  intervening  between  them.  This  expe- 
riment might  seem  to  indicate,  that  the  periosteum  itself  forms  the 
bone ;  but  the  real  production  of  new  tissue, — as  in  cases  where  the 
periosteum  has  been  detached  by  disease,  and  remains  alive  whilst 
the  shaft  dies, — is  in  continuity  with  minute  spicula  of  the  original 
bone,  which  still  adhere  to  the  periosteum.*  Again,  we  find  that  in 
comminuted  fractures,  every  portion  of  the  shattered  bone  that  remains 
connected  with  the  vascular  membranes,  whether  these  be  the  internal 
or  the  external,  becomes  the  centre  of  a  new  formation  ;  and  that  the 
loss  of  substance  is  filled  up  the  more  rapidly,  in  proportion  to  the 
number  of  such  centres. 

308.  The  reparation  of  Bone,  after  disease  or  injury,  takes  place 
exactly  upon  the  same  plan  as  its  first  formation.  A  plastic  or  organ- 
izable  exudation  is  first  poured  out  from  the  neighbouring  blood-ves- 
sels, and  this  forms  a  sort  of  bed  or  matrix,  in  which  the  subsequent 
processes  take  place.  Next,  a  cartilaginous  substance  is  formed,  as 
in  the  embryo,  by  the  attraction  of  gelatinous  intercellular  substance 
to  the  exterior  of  certain  cells,  and  this  is  gradually  converted  into 
Bone,  by  the  regular  process  of  ossification.  When  the  shaft  of  a 
long  bone  has  been  fractured  through,  and  the  extremities  have  been 
brought  evenly  together,  it  is  found  that  the  new  matter  first  ossified 
is  that  which  occupies  the  central  portion  of  the  deposit,  and  which 
thus  connects  the  medullary  cavities  of  the  broken  ends,  forming  a 
kind  of  plug  that  enters  each.  This  was  termed  by  Dupuytren,  by 
whom  it  was  first  distinctly  described,  Xhe  provisional  callus.  This  is 
usually  formed  in  the  course  of  five  or  six  weeks,  or  less  in  young 
persons ;  but  at  that  period  the  contiguous  surfaces  of  the  bone  itself 
are  not  cemented  by  bony  union  ;  and  the  formation  of  the  permanent 
callus  occupies  some  months,  during  which  the  provisional  callus  is 
gradually  absorbed,  and  the  continuity  of  the  medullary  canal  restored, 
in  the  same  manner  as  it  was  at  first  established.  The  permanent 
callus  has  all  the  characters  of  true  bone. 

309.  The  most  extensive  reparation  is  seen,  when  the  shaft  of  a 
long  bone  is  destroyed  by  disease.  If  violent  inflammation  occur  in 
its  tissue,  the  death  of  the  fabric  is  frequently  the  consequence, — appa- 
rently through  the  blocking-up  of  the  canals  with  the  products  of  the 
inflammatory  action,  and  the  consequent  cessation  of  the  supply  of 
nutriment.  It  is  not  often  that  the  whole  thickness  of  the  bone 
becomes  necrosed  at  once ;  more  commonly  this  result  is  confined  to 
its  outer  or  its  inner  layers.  When  this  is  the  case,  the  new  formation 
takes  place  from  the  part  that  remains  sound  ;  the  external  layers, 
which  receive  their  vascular  supply  from  the  periosteum  and  from  the 
Haversian  canals  continued  inwards  from  it,  throwing  out  new  matter 
on  their  interior,  which  is  gradually  converted  into  bone;  whilst  the 
internal  layers,  if  they  should  be  the  parts  remaining  uninjured,  do 

*  See  Mr.  J.  Goodsir  on  the  Reproduction  of  Bone,  in  his  Anatomical  and  Patho- 
logical Researches. 


192 


FORMATION  OF  TEETH.—DENTINE. 


the  same  on  their  exterior,  deriving  their  materials  from  the  medul- 
lary membrane  and  its  prolongations  into  their  Haversian  canals.  But 
it  sometimes  happens  that  the  whole  shaft  suffers  necrosis  ;  and  as 
the  medullary  membrane  and  the  entire  system  of  Haversian  canals 
have  lost  their  vitality,  reparation  can  only  take  place  from  the  splin- 
ters of  bone  which  remain  attached  to  the  periosteum,  and  from  the 
living  bone  at  the  two  extremities.  This  is  consequently  a  very  slow 
process ;  more  especially  as  the  epiphyses,  having  been  originally 
formed  as  distinct  parts  from  the  shaft,  do  not  seem  able  to  contribute 
much  to  the  regeneration  of  the  latter.* 

310.  We  next  proceed  to  the  Teeth^  which  are  organs  of  mechanical 
attrition,  developed  in  the  first  part  of  the  alimentary  canal,  for  the 

purpose   of  comminuting  the  food  con- 
^'^■^^-  veyed  into  it.     Their  place  of  origin  is 

altogether  different  from  that  of  bone,  as 
they  commence  in  little  papillary  eleva- 
tions of  the  mucous  membrane  covering 
the  jaw;  but  the  substance  from  which 
they  are  formed  is  the  same  primitive 
cellular  tissue,  as  that  in  which  Cartilage 
itself  originates.  We  may  best  under- 
stand the  structure  and  development  of 
the  Teeth  in  Man,  by  first  inquiring  into 
the  characters  presented  by  those  of  some 
of  the  lower  animals,  and  the  history  of 
their  evolution.  In  the  foetal  Shark,  the 
first  appearance  of  the  tooth  is  in  the  form 
of  a  minute  papilla  on  the  mucous  mem- 
brane covering  the  jaws;  the  substance  of 
this  papilla  is  composed  of  spherical  cells, 
which  are  imbedded  in  a  kind  of  gela- 
tinous substance  resembling  that  of  inci- 
pient cartilage  ;  whilst  its  exterior  is  com- 
posed of  a  dense,  structureless,  pellucid 
membrane.  The  cellular  mass  is  not  at 
first  permeated  by  vessels;  but  a  small 
arterial  branch  is  distributed  to  each  papilla,  and  spreads  out  into  a 
tuft  of  capillaries  at  its  base  (Fig.  50).  The  papilla  gradually  enlarges, 
by  the  formation  of  new  cells  at  the  part  immediately  adjacent  to  the 
blood-vessels,  which  supply  the  material  requisite  for  their  develop- 
ment;  and  when  it  has  acquired  its  full  size,  the  process  o^  calcifica- 
tion takes  place,  by  which  it  is  converted  into  Dentine, — the  substance 
most  characteristic  of  teeth. 

311.  This  Dentine,  which  in  the  Elephant's  tusk  is  known  as  Ivory, 

*  For  many  parts  of  the  foregoing  account  of  the  structure  and  development  of 
Bone,  the  Author  is  indebted  to  the  Chapter  on  that  subject  in  Messrs.  Todd  and 
Bowman's  Physiological  Anatomy,  as  well  as  to  the  papers  of  Mr.  Goodsir  already 
referred  to. 


Vessels  of  Dental  Papilla. 


STRUCTURE  OF  DENTINE. 


193 


Fig.  51. 


Oblique  section  of  Dentine  of  hu^- 
man  tooth,  highly  magnified,  show- 
ing the  calcigerous  tubuli,  and  lh« 
outlines  of  the  original  cells. 


is  a  firm  substance,  in  which  mineral  matter  predominates  to  a  greater 
extent  than  in  bone;  but  which  still  has  a  definite  animal  basis,  that 
retains  its  form  when  the  calcareous  matter  has  been  removed  by 
maceration  in  acid.  In  every  100  parts,  the  animal  matter  fi^rms 
about  28  ;  and  of  the  mineral  portion  phosphate  of  lime  constitutes 
about  64J  parts,  carbonate  of  lime  5J  parts,  and  phosphates  of  mag- 
nesia and  soda,  with  chloride  of  sodium,  about  2J  parts.  When  it 
is  fractured,  it  seems  to  possess  a  fibrous 
appearance ;  the  fibres  radiating  from  the 
centre  of  the  tooth  towards  its  circumfe- 
rence. Bat  when  a  thin  section  of  it  is 
submitted  to  the  microscope,  it  is  seen  that 
this  fibrous  appearance  is  due  to  a  peculiar 
structure  in  the  dentine,  which  the  unaided 
eye  cannot  discover.  The  dentinal  sub- 
stance is  itself  very  transparent;  but  it  is 
traversed  by  minute  tubuli,  which  appear 
as  dark  lines,  generally  in  very  close  ap- 
proximation, running  from  the  internal  por- 
tion of  the  tooth  towards  the  surface,  and 
exhibiting  numerous  minute  undulations, 
and  sometimes  more  decided  curvatures,  in 
their  course.  They  occasionally  divide 
into  two  branches,  which  continue  to  run 
at  a  little  distance  from  one  another  in  the  same  direction;  and  they 
also  frequently  give  off  small  lateral  branches,  which  again  sencl  off" 
smaller  ones.  In  some  animals,  the  tubuli  may  be  traced  at  their 
extremities  into  minute  cells,  or  cavities,  analogous  to  the  lacunae 
of  bone ;  and  the  lateral  branchlets  occasionally  terminate  in  such 
cavities,  which  are  called  the  intertubular  cells.  The  diameter  of 
the  tubuli  at  their  largest  part  averages  l-10,000th  of  an  inch  ;  their 
smallest  branches  are  immeasurably  fine.  It  is  impossible  that  even 
the  largest  of  them  can  receive  blood,  as  their  diameter  is  far  less- 
than  that  of  the  blood-discs ;  but  it  is  probable  that,  like  the  canali* 
culi  of  bone,  they  may  absorb  nutrient  matter  from  the  vascular  sur~ 
face,  with  which  their  internal  extremities  are  in  relation. 

312.  In  the  Teeth  of  Man  and  of  most  Mammalia,  we  find  the 
central  portion  hollow ;  and  lined,  in  the  living  tooth,  by  a  vascular 
membrane.  This  cavity,  with  its  vascular  wall,  is  analogous  to  an 
enlarged  cancellus  or  Haversian  canal  of  Bone  ;  and,  as  we  shall  pre- 
sently see,  it  is  formed  in  a  similar  manner.  Upon  the  walls  of  the 
cavity,  all  the  tubuli  open ;  and  they  radiate  from  this  towards  the 
surface  of  the  upper  part  of  the  tooth,  as  shown  in  the  accompanying- 
figure.  The  central  cavity  is  continued  as  a  canal  through  each  fang- 
or  root ;  and  the  dentinal  tubes  in  like  manner  radiate  from  this,, 
towards  the  surface  of  the  fang. — In  the  teeth  of  many  of  the  lower 
animals,  however,  we  find  a  network  of  canals  extending  through  the 
substance  of  the  tooth,  instead  of  a  single  cavity;  and  these  canals  are 


194       STRUCTURE  AND  DEVELOPMENT  OF  DENTINE. 

frequently  continuous  with  the  Haversian  canals  of  the  subjacent  bone, 
so  that  the  analogy  between  the  two  is  complete.  From  each  canal 
the  dentinal  tubuli  radiate,  just  in  the  manner  of  the  canaliculi  of  bone 
(§  279);  and  thus  we  may  regard  a  tooth  of  this  kind  as  repeating,  in 
each  of  the  parts  surrounding  one  of  these  canals,  the  structure  of  the 
human  tooth. 

313.  The  process  by  which  the  cellular  mass,  or  pulp,  of  the  dental 
papilla,  becomes  converted  into  the  dentine  of  the  perfect  tooth,  is 
thus  described  by  Prof.  Owen,  from  his  investigations  into  the  his- 
tory of  the  Shark's  dentition. — The  pulp  becomes  vascular,  by  the 
extension  of  the  capillary  network  into  its  substance  ;  the  vessels  are 
also  accompanied  by  fine  branches  of  nerves.  The  cells  arrange 
themselves  in  lines,  radiating  from  the  centre  to  the  circumference  of 
the  pulp  ;  and  they  become  somewhat  elongated  in  that  direction.  A 
series  of  changes  takes  place  in  the  nuclei  of  the  cells,  consisting 
chiefly  in  their  elongation  and  subdivision;  so  that  they  form  a  series 
of  parallel  lines  within  each  cell.  The  subdivided  and  elongated 
nuclei  become  attached,  by  their  extremities,  to  the  corresponding 
(nuclei  of  the  cells  in  advance,  and  the  attached  extremities  form  con- 
tinuous lines;  so  that  in  each  row  or  file  of  cells,  extending  from  the 
inner  part  to  the  circumference  of  the  pulp,  there  are  several  dark 
lines,  apparently  continuous,  which  are  formed  by  rows  of  granules 
(or  perhaps  incipient  cells)  thus  derived  from  the  once  single  and 
Tounded  nuclei  of  the  parent-cells.  During  the  same  time,  the  walls 
«of  the  adjacent  cells  come  into  closer  proximity,  to  the  exclusion  of 
the  gelatinous  matter,  that  originally  intervened  between  them  ;  and 
they  secrete  calcareous  matter,  derived  from  the  blood,  into  their  own 
cavities.  The  cells  thus  become  completely  filled  with  that  material 
(probably  combined  with  gelatin,  as  in  bone),  excepting  in  the  part 
•occupied  by  the  rows  of  granules,  which  are  thus  left  unconsolidated; 
and  which,  when  the  granules  disappear  at  a  subsequent  period, 
remain  as  the  dentinal  tubes.  This  consolidation  first  takes  place  on 
the  exterior  of  the  pulp  ;  and  the  calcifying  process  gradually  extends 
itself  inwards,  causing  the  blood-vessels  to  retreat,  as  it  were,  towards 
the  centre,  where  an  unconsolidated  portion  usually  remains. 

314.  Thus  the  substance  of  the  outer  portion  of  the  pulp  is  actually 
•converted  into  dentine,  and  does  not  form  it  by  a  process  of  excretion, 
as  was  formerly  supposed.  In  general,  the  coalescence  of  the  original 
cells  is  so  complete,  that  their  boundaries  altogether  disappear,  and 
the  substance  that  intervenes  between  the  tubuli  seems  quite  homo- 
geneous; but  distinct  traces  of  the  original  division  into  cells  may 
•often  be  met  with,  in  the  dentine  of  Man  (Fig.  50),  as  well  as  in  that 
of  other  animais  ;  which  satisfactorily  confirms  what  has  been  just 
stated,  as  to  the  mode  of  its  formation.  Although  in  the  most  charac- 
teristic form  of  Dentine,  no  blood-vessels  exist,  yet  there  are  certain 
«pecies,  both  among  Mammals,  Reptiles,  and  Fishes,  in  which  the 
Dentine  is  traversed  by  cylindrical  prolongations  of  the  central  cavity, 
•convejing  blood-vessels  into  its  substance  ;  and  the  presence  of  these 


STRUCTURE  AND  DEVELOPMENT  OF  DENTINE.       195 

medullary  canals  thus  gives  to  the  Dentine  a  vascular  character ;  and 
thus  increases  its  resemblance  to  bone. — The  central  portion  of  the 
pulp  is  sometimes  converted  into  a  substance  still  more  nearly  resem- 
bling bone,  having  its  stellate  lacunae  as  well  as  its  vascular  canals. 
This  change  is  normal  or  regular  in  certain  animals,  as  in  the  extinct 
Iguanodon  and  Icthosaurus,  and  in  the  Cachalot  or  Sperm-whale  ;  and 
the  ossified  pulp  bears  a  close  resemblance  to  the  bones  of  the  respect- 
ive animals,  although  it  is  not  formed  in  continuity  with  them.  A 
similar  change  occurs  in  the  Human  tooth; — sometimes,  it  would 
appear,  rapidly,  as  the  result  of  disease ;  but  in  general  more  slowly, 
increasing  gradually  with  the  advance  of  age. 

315.  It  is  not  easy  to  ascertain  the  amount  of  nutritive  change  that 
takes  place  in  the  substance  of  Dentine,  when  it  is  once  fully  formed. 
When  young  animals  are  fed  with  colouring-matter,  it  is  found  to 
tinge  their  teeth,  as  well  as  their  bones  ;  and  if  the  tooth  be  in  process 
of  rapid  formation  at  the  time  of  the  experiment,  the  progressive  cal- 
cification of  the  pulp,  from  without  inwards,  is  marked  by  a  series  of 
concentric  lines.  Even  in  the  adult,  some  tinge  will  result  from  a 
prolonged  use  of  this  substance  ;  and  it  has  been  noticed  that  the 
teeth  of  persons,  who  have  long  suflTered  from  Jaundice,  sometimes 
acquire  a  tinge  of  bile.  These  facts  show  that,  even  after  the  com- 
plete consolidation  of  the  Dentine,  it  is  still  pervious  to  fluids:  and 
that  in  this  manner  it  may  draw  into  itself,  from  the  vascular  lining 
of  the  pulp-cavity,  a  substance  capable  of  repairing  its  structure,  is 
proved  by  the  circumstance,  that  a  new  layer  of  hard  matter  is  occa- 
sionally thrown  out  upon  a  surface  which  has  been  laid  bare  by  caries. 

316.  In  those  simple  teeth  which  consist  solely  of  Dentine,  the 
mode  of  production  already  described, — that  of  the  consolidation  of  a 
papilla  upon  the  mucous  membrane  of  the  mouth, — is  all  which  is 
requisite.  When  the  formation  of  the  tooth  itself  is  complete,  it  may 
remain  attached  only  to  the  mucous  membrane,  which  is  the  case  in 
the  Shark,  or  it  may  grow  downwards,  by  the  addition  of  new  dental 
structure  at  its  base,  until  it  comes  in  contact  with  the  bone  of  the 
jaw.  Where  it  is  only  attached  to  the  mucous  membrane,  as  in  the 
Shark,  it  is  very  liable  to  be  torn  away  ;  but  a  new  tooth,  formed  from 
a  distinct  papilla,  is  ready  to  replace  it;  and  this  process  is  continually 
repeated,  the  development  of  new  papillae  being  apparently  unlimited. 
On  the  other  hand,  where  the  root  of  the  tooth  comes  in  contact  with 
the  jaw,  it  may  completely  coalesce  with  it,  which  is  the  case  in  many 
Fishes,  the  Haversian  canals  of  the  bone  being  continued  as  medullary 
canals  into  the  dentine  ;  or  it  may  send  long  spreading  roots  into  the 
bone,  which  are  united  to  it  at  their  extremities.  In  the  classes  of 
Fishes  and  Reptiles  (with  scarcely  any  exceptions)  the  teeth  are  by 
no  means  permanent,  as  among  Mammalia;  but  new  teeth  are  con- 
tinually succeeding  the  old  ones.  The  mode  in  which  these  teeth 
originate,  by  small  buds  from  the  capsules  of  the  preceding,  will  be 
understood  when  the  capsular  development  of  all  the  higher  forms  of 
the  dental  apparatus  has  been  described. 


196 


STRUCTURE  OF  ENAMEL. 


317.  It  is  obvious  that  there  is  no  provision,  in  the  simple  calcifi- 
cation of  the  dental  papilla,  for  any  variations  or  density,  other  than 
those  which  may  result  from  the  different  degrees  of  hardness  in  the 
substance  of  the  dentine  itself.  Now  in  the  teeth  of  Man  and  most 
other  Mammals,  and  in  those  of  many  Reptiles  and  some  Fishes,  we 
find  two  other  substances,  one  of  them  harder,  and  the  other  softer, 
than  Dentine;  the  former  is  termed  Enamel;  and  the  latter  Cementum 
or  Crusta  petrosa.  For  the  development  of  these,  a  peculiar  modifi- 
cation of  the  apparatus  is  requisite. 

318.  The  Enamel  is  composed  of  long  prismatic  cells,  exactly 
resembling  those  of  the  prismatic  shell-substance  formerly  described, 
but  on  a  for  more  minute  scale  ;  the  diameter  of  the  cells  not  being 
more,  in  Man,  than  l-5600th  of  an  inch.  The  length  of  the  prisms 
corresponds  with  the  thickness  of  the  layer  of  enamel ;  and  the  two 
surfaces  of  this  layer  present  the  ends  of  the  prisms,  which  are  usually 
more  or  less  regularly  hexagonal.  The  quantity  of  animal  matter 
in  the  tooth  of  the  adult  is  extremely  minute, — not  above  two  parts 
in  100  ;  and  it  is  only  at  a  very  early  age,  that  the  true  character  of 
the  animal  structure  can  be  distinctly  seen.  The  course  of  the  pris- 
matic cells  is  more  or  less  wavy  ;  and  they 

F'g-52.  are  marked  by  numerous  transverse  striae, 

resembling  those  of  the  prismatic  shell-sub- 
stance, and  probably  originating  in  the  same 
cause, — the  coalescence  of  a  line  of  shorter 
cells,  to  form  the  lengthened  prism.  No 
trace  of  tubuli  or  of  blood-vessels  is  to  be 
found  in  the  completely  formed  Enamel  of 
higher  animals  ;  but  in  the  teeth  of  certain 
Fishes,  it  is  penetrated  by  calcigerous  tubes, 
which  enter  its  substance  from  the  exterior, 
and  ramify  and  subdivide  like  those  of  the 
dentine.  Of  the  98  parts  of  mineral  matter 
in  the  enamel,  88^  consist  (according  to 
Berzelius)  of  phosphate  of  lime,  8  of  car- 
bonate of  lime,  and  IJ  of  phosphate  of 
magnesia.  In  density  and  resisting  power, 
the  Enamel  far  surpasses  any  other  organ- 
ized tissue,  and  approaches  some  of  the 
hardest  of  mineral  substances.  In  Man, 
and  in  Carnivorous  animals,  it  covers  the 
crown  of  the  tooth  only,  with  a  simple  cap 
or  superficial  layer  of  tolerably  uniform  thickness  (Fig.  52,  1), 
which  follows  the  surface  of  dentine  in  all  its  inequalities ;  and  its 
component  prisms  are  directed  at  right  angles  to  that  surface,  their 
inner  extremities  resting  in  slight  but  regular  depressions  on  the  exte- 
rior of  the  dentine.  In  the  teeth  of  many  Herbivorous  animals,  how- 
ever, the  Enamel  forms  (with  the  Cementum)  a  series  of  vertical 
plates,  which  dip  down  (as  it  were)  into  the  substance  of  the  dentine, 


Vertical  section  of  human  mo- 
lar tooih;— 1,  enamel ;  2,  cemen- 
tum or  crusta  petrosa;  3.  dentine 
or  ivory  ;  4.  osseous  excrescence, 
arising  from  hypertrophy  of  ce- 
mentum; 5,  cavity;  6,  osseous 
cells  at  outer  pan  of  dentine. 


CEMENTUM.— FORMATION  OF  DENTAL  CAPSULE.  197 

and  present  their  edges  alternately  with  it,  at  the  grinding  surface  of 
the  tooth  ;  and  there  is  in  such  teeth  no  continuous  layer  of  dentine 
over  the  crown.  The  purpose  of  this  arrangement  is  evidently  to 
provide,  by  the  unequal  wear  of  these  three  substances, — of  which 
the  Enamel  is  the  hardest  and  the  Cementum  the  softest, — for  the 
constant  maintenance  of  a  rough  surface,  adapted  to  triturate  the 
tough  vegetable  substances  on  which  these  animals  feed. — The 
Enamel  is  the  least  constant  of  the  Dental  tissues.  It  is  more  fre- 
quently absent  than  present  in  the  teeth  of  the  class  of  Fishes ;  it  is 
wanting  in  the  entire  order  of  Ophidia  (Serpents)  among  existing 
Reptiles ;  and  it  forms  no  part  of  the  teeth  of  the  Edentata  (Sloths, 
&c.)  and  Cetacea  (Whales)  amongst  Mammals. 

319.  The  Cementum,  or  Crusta  Petrosa,  has  the  characters  of  true 
bone ;  possessing  its  distinctive  stellate  lacunae  and  radiating  canali- 
culi.  Where  it  exists  in  small  amount,  we  do  not  find  it  traversed  by 
medullary  canals ;  but,  like  Dentine,  it  is  occasionally  furnished  with 
them,  and  thus  resembles  Bone  in  every  particular.  These  medullary 
canals  enter  its  substance  from  the  exterior  of  the  tooth  ;  and  conse- 
quently pass  towards  those,  which  radiate  from  the  central  cavity 
towards  the  surface  of  the  dentine,  where  it  possesses  a  similar  vas- 
cularity,— as  was  remarkably  the  case  in  the  teeth  of  the  extinct 
Megatherium. — In  the  Human  tooth,  however,  the  Cementum  has  no 
such  vascularity.  It  forms  a  thin  layer,  which  envelops  the  root  of 
the  tooth,  commencing  near  the  termination  of  the  capping  of  Enamel 
(Fig.  52, 2).  This  layer  is  very  subject  to  have  its  thickness  increased, 
especially  at  the  extremity  of  the  fangs,  by  hypertrophy,  resulting 
from  inflammation  ;  and  sometimes  large  exostoses  are  thus  formed 
(Fig.  52,  4),  which  very  much  increase  the  difficulty  of  extracting  the 
tooth.  When  the  tooth  is  first  developed,  the  Cementum  envelops 
its  crown,  as  well  as  its  body  and  root ;  but  the  layer  is  very  thin 
where  it  covers  the  Enamel,  and  being  soft,  it  is  soon  worn  away  by 
use.  In  the  teeth  of  many  Herbivorous  Mammals,  it  dips  down  with 
the  Enamel  to  form  the  vertical  plates  of  the  interior  of  the  tooth  ;  and 
in  the  teeth  of  the  Edentata  as  well  as  of  many  Reptiles  and  Fishes, 
it  forms  a  thick  continuous  envelop  over  the  whole  of  the  surface, 
until  worn  away  at  the  crown. 

320.  The  development  of  these  additional  structures  is  provided 
for  by  the  enclosure  of  the  primitive  papilla,  from  which  the  Dentine 
is  formed,  within  a  Capsule,  which,  at  one  period,  completely  covers 
it  in :  between  the  inner  surface  of  the  capsule,  and  the  outer  surface 
of  the  dentinal  papilla,  a  sort  of  epithelium  is  developed,  by  the  cal- 
cification of  which,  the  Enamel  is  formed ;  and  the  Cementum  is 
generated  by  the  conversion  of  the  capsule  itself  into  a  bony  sub- 
stance.— The  processes  by  which  this  capsular  investment  is  pro- 
duced, and  the  tooth  completed  and  evolved,  will  now  be  briefly 
described,  as  they  occur  in  the  Human  foetus. 

321.  The  dental  papillae  begin  to  make  their  appearance,  at  about 
the  seventh  week  of  embryonic  life,  upon  the   mucous   membrane 


198  DEVELOPMENT  OF  HUMAN  TEETH. 

covering  the  bottom  of  a  deep  narrow  groove  (Fig.  53,  a),  that  runs 
alon^  the  edge  of  the  jaw  (Fig.  53,  b);  and  during  the  tenth  week, 
processes  from  the  sides  of  this  "  primitive  dental  groove,"  particu- 

Fig.  53. 


Successive  stages  of  the  development  of  the  deciduous  or  temporary  teeth,  and  of  the  origin  of  the 
sacs  of  the  permanent  set. 

larly  the  external  one,  begin  to  approach  one  another,  so  as  to  divide 
it,  by  their  meeting,  into  a  series  of  open  follicles,  at  the  bottom  of 
which  the  papillae  may  still  be  seen.  At  the  thirteenth  week,  all  the 
follicles  being  completed,  the  papillae,  which  were  at  first  round  blunt 
masses  of  cells,  begin  to  assume  forms  more  characteristic  of  the  teeth 
which  are  to  be  developed  from  them  ;  and  by  their  rapid  growth, 
they  protrude  from  the  mouths  of  the  follicles  (Fig.  53,  c).  At  the 
same  time,  the  edges  of  the  follicles  are  lengthened  into  little  valve- 
like processes,  or  opercula,  which  are  destined  to  meet  and  form 
covers  to  the  follicles  (Fig.  53,  d).  There  are  two  of  these  opercula 
in  the  Incisive  follicles,  three  for  the  Canines,  and  four  or  five  for  the 
Molars.  And  by  the  fourteenth  week,  the  two  lips  of  the  dental 
groove  meet  over  the  mouths  of  the  follicles,  so  as  completely  to 
enclose  each  papilla  in  a  distinct  capsule  (Fig,  53,  e).  At  this  period, 
before  the  calcification  of  the  primitive  pulps  commences,  a  provision 
is  made  for  the  production  of  the  second  or  permanent  molars  ;  whose 
capsules  originate  in  buds  or  offsets  from  the  upper  part  of  the  cap- 
sules of  the  temporary  or  milk-teeth  (Fig.  53,/).  These  offsets  are 
in  the  condition  of  open  follicles,  communicating  with  the  cavity  of 
the  primitive  tooth  ;  but  they  are  gradually  closed  in,  and  detached 
altogether  from  the  capsules  of  the  milk-teeth  (Fig.  53,  g,  A,  i). 

322.  Soon  after  the  closure  of  the  follicles  of  the  Milk-teeth,  the 
conversion  of  the  cells  of  the  original  papilla  into  Dentine  commences, 
according  to  the  method  already  described  (§  313).  Whilst  this  is 
going  on,  the  follicles  increase  in  size,  so  that  a  considerable  space  is 
left  between  their  inner  w^alls  and  the  surface  of  the  dental  papillae  ; 
which  space  is  filled  up  with  a  gelatinous  granular  matter,  the  Enamel- 
pulp.  The  portion  of  this  which  is  converted  into  enamel,  however, 
is  very  small ;  being  only  a  thin  layer,  which  is  left  on  the  inner  sur- 
face of  the  capsule  after  the  remainder  has  disappeared.  The  interior 
of  the  dental  sac,  at  the  time  when  the  conversion-process  has  reached 
the  base  of  the  dentinal  pulp,  is  in  the  villous  and  vascular  condition 


DEVELOPMENT  AND  RENEWAL  OF  TEETH.  199 

of  a  Mucous  membrane, — which  indeed  it  really  is,  having  been,  as 
we  have  seen,  once  continuous  with  the  lining  of  the  mouth  ;  and  the 
layer  of  prismatic  cells  which  covers  its  free  surface,  and  by  the  cal- 
cification of  which  the  enamel  is  produced,  may  be  regarded  as  an 
epithelium. — The  completion  of  the  Enamel,  and  the  ossification  of 
the  capsule  so  as  to  form  the  Cementum,  take  place  at  a  subsequent 
period. 

323.  We  have  thus  seen  that  the  history  of  the  first  development 
of  the  human  teeth  may  be  divided  into  three  stages,  the  papillary, 
the  follicular,  and  the  saccular.  The  papillary  corresponds  precisely 
with  the  complete  mode  of  dental  development  in  the  Shark  and 
other  Fish, — as  already  mentioned.  The  follicular,  which  commences 
with  the  enclosure  of  the  papilla  in  open  follicles,  and  terminates 
when  the  papillae  are  completely  hidden  by  the  closure  of  the  mouths 
of  those  follicles,  has  also  its  permanent  representation  in  the  develop- 
ment of  the  teeth  of  many  Reptiles  and  Fishes  ;  the  primitive  papillae 
of  which,  though  enclosed  in  follicles,  are  never  covered  in  at  the 
summit,  and  thus  free  themselves  from  their  envelops  by  simply 
growing  upwards  through  their  open  mouths.  But  in  Man,  in  all 
other  animals  which  agree  with  him  in  going  on  to  the  saccular  stage, 
there  must  also  be  an  eruptive  stage,  which  consists  in  the  bursting- 
forth  of  the  tooth  from  the  enclosing  capsule  ;  the  summit  of  the  tooth 
being  carried  against  the  lid  of  the  sac,  by  the  growth  of  its  root  (Fig. 
53,  h).  By  the  continuance  of  the  same  growth,  the  teeth  are  caused 
to  penetrate  the  gum,  and  are  gradually  raised  above  its  surface  (Fig. 
53,  i). 

324.  All  the  permanent  teeth,  which  are  destined  to  replace  the 
temporary  set,  originate,  as  already  stated,  in  buds  or  offsets  from  the 
capsules  of  the  latter.  But  behind  the  last  temporary  molars,  which 
are  replaced  by  the  permanent  bicuspids,  three  permanent  molars  are 
to  be  developed,  on  each  side  of  either  jaw.  The  Jlrst  of  these  is 
formed  on  precisely  the  same  plan  with  the  milk-teeth ;  but  is  not 
completed  until  a  later  period.  The  capsule  of  the  second  is  formed 
at  a  later  period  from  that  of  the  first,  by  a  process  of  budding  ex- 
actly analogous  to  that  by  which  the  other  permanent  capsules  are 
formed  from  the  corresponding  temporary  ;  and  at  a  still  later  period, 
the  capsule  of  the  third  permanent  molar  is  formed  as  a  bud  from  that 
of  the  second.  The  evolution  of  this  molar  does  not  usually  take 
place  until  the  system  has  acquired  its  full  development ;  and  the 
process  of  budding  then  ceases  in  Man, — being  limited  to  a  single 
act  of  reproduction  in  the  case  of  the  ordinary  Milk-teeth,  and  to  a 
double  one  in  that  of  the  first  permanent  Molar.  In  many  animals  of 
the  lower  classes,  however,  the  process  goes  on  through  the  whole  of 
life  without  any  limit;  the  newly-formed  teeth,  however,  usually 
replacing  those  of  the  previous  set,  and  not  being  developed  at  their 
sides  like  the  second  and  third  permanent  molars  of  Man. 

325.  By  a  process  of  this  kind,  the  continual  renewal  of  the  Teeth 
takes  place  in  those  Reptiles  and  Fishes,  whose  dentition  goes  on  to 


200 


DEVELOPMENT  AND  SUCCESSION  OF  TEETH. 


the  saccular  stage ;  in  those  at  which  it  stops  at  the  papillary,  the 
successive  teeth  are  formed  from  new  and  independent  papillae.  The 
only  exception  to  the  rule,  that  no  Reptiles  or  Fishes  have  permanent 
teeth,  is  found  in  the  curious  Dicynodon ;  an  extinct  Reptile  which 
had  two  large  tusks  growing  from  persistent  pulps,  like  those  of  the 
Elephant,  the  front  teeth  of  the  Rodentia,  and  the  grinders  of  the 
Edentata.  In  such  teeth,  the  base  of  the  pulp  remains  unconverted, 
and  a  new  development  of  cells  is  continually  taking  place  in  that 
situation  ;  these  new  cells  are  in  their  turn  converted  into  dentine,  in 
continuity  with  that  previously  formed  ;  and  thus  the  toolh  or  tusk  is 
continually  lengthening  at  its  base,  in  a  degree  which  compensates  for 
its  usual  wear  at  its  summit.  If  anything  should  prevent  that  wear, 
— as  when  the  opposite  tooth  has  been  broken  off, — there  is  an  abso- 
lute increase  in  the  length  of  the  tooth,  from  the  continued  growth  at 
its  base ;  which  may  become  a  source  of  great  inconvenience  to  the 
animal.  There  is  nothing,  in  the  human  subject,  at  all  analogous  to 
this  mode  of  development  from  persistent  pulps ;  the  process  being 
checked  by  the  closure  of  the  root  around  the  base  of  the  pulp,  which 
obstructs  the  supply  of  blood  it  receives.  The  analogy  between  the 
continued  succession  of  teeth  in  the  lower  Vertebrata,  by  the  gem- 
miparous  reproduction  of  their  capsules,  and  the  development  of  the 
capsules  of  the  permanent  teeth  of  Man  from  those  of  the  temporary 
set,  is  made  further  evident  by  the  fact,  that  a  third  set  occasionally 
makes  its  appearance  in  persons  advanced  in  life ;  the  development 
of  which  would  not  be  intelligible,  if  we  could  not  refer  it  to  the 
continuance  of  the  same  process  in  the  other  capsules,  as  that  which 
regularly  takes  place  to  a  limited  extent  in  the  permanent  molars  of 
Man,  and  which  goes  on  without  limit  through  the  whole  lives  of  the 
lower  Vertebrata. 

326.  The  following  table  shows  the  usual  periods  at  which  the 
different  teeth  of  the  two  sets  first  show  themselves  above  the  gum. 
It  must  be  borne  in  mind,  however,  that  these  periods  are  subject  to 
very  great  variation;  and  that  the  average  alone  can  therefore  be 
expressed. 


Temporary  or 

Deciduous  Teeth. 

Permanent  Teeth, 

Months. 

Years. 

Central  Incisors 

.      •         7 

First  Molar             .     6J  to  7 

Lateral  Incisors 

.       8—10 

Central  Incisors     .     7  —  8 

Anterior  Molars 

.     12—13 

Lateral  Incisors      .     8  —  9 

Canines 

.     14—20 

First  Bicuspid        .     9  —10 

Posterior  Molars 

.     18—36 

Second  Bicuspid    .  10  — 11 
Canines         .         .  12  — 12J 
Second  Molars       .   12J— 14 
Third  Molars          .  16  —30 

327.  We  have  seen  that  the  Teeth  are  formed,  in  the  first  instance, 
upon  the  surface  of  the  Mucous  membrane  of  the  mouth ;  and  con- 


STRUCTURE  AND  DEVELOPMENT  OF  HAIR.         201 

sequently  they  really  form  a  part  of  the  external  or  dermo-skeleton, 
and  not  of  the  internal  or  osseous  skeleton.  They  correspond,  there- 
fore, with  the  external  skeletons  of  the  Invertebrata ;  and  thus  the 
analogy  which  has  been  pointed  out,  between  the  enamel  of  teeth 
and  the  prismatic  cellular  substance  of  the  shells  of  Mollusca,  and 
between  the  dentine  and  the  shells  of  the  higher  Crustacea,  holds 
good  also  in  regard  to  the  situation  of  these  structures.  Although  the 
teeth  are  the  only  ossified  portions  of  the  dermo-skeleton  in  Man,  we 
find  the  body  partially  or  completely  enclosed  in  an  armour  of  bony 
scales  or  plates,  in  certain  Mammalia,  Reptiles,  and  Fishes ;  and  in 
some  species  of  the  last-named  class,  which  have  now  ceased  to  exist, 
the  scales  seem  to  have  had  the  texture  of  Enamel. 

328.  In  connection  with  the  teeth,  the  structure  and  development 
of  the  Hair  may  be  described  ;  this  substance  being  generated  very 
much  in  the  same  manner  as  dentine, — by  the  conversion  of  a  pulp 
enclosed  in  a  follicle ;  though  the  product  of  the  transformation  is 
different.  The  Hair-follicle  is  formed  by  the  inversion  of  the  Skin, 
as  the  Tooth-follicle  is  by  an  inversion  of  the  Mucous  membrane ; 
and  it  is  lined  by  a  continuation  of  the  epidermis.  From  the  bottom 
of  the  follicle,  a  sort  of  papilla  rises  up,  formed  of  cells ;  the  exterior 
of  this,  which  is  the  densest  part,  is  known  as  the  bulb  ;  whilst  the 
softer  interior  is  termed  the  pulp.  The  follicle  itself  is  extremely 
vascular ;  and  even  the  bulb  is  reddened  by.  a  minute  injection ; 
though  no  distinct  vessels  can  be  traced  into  it. — It  has  been  imag- 
ined until  recently,  that  the  Hair,  like  the  other  extra-vascular  tissues, 
is  a  mere  product  of  secretion  ;  its  material,  which  is  chiefly  horny 
matter  of  the  same  composition  with  that  of  the  epidermis  and  its 
other  appendages  (§227),  being  elaborated  from  the  surface  of  the 
pulp.  This,  however,  proves  to  be  a  very  erroneous  account  of  it ; 
as  is  shown  by  the  results  of  recent  microscopic  inquiries  into  its 
structure.  Although  the  Hairs  of  different  animals  vary  considerably 
in  the  appearances  they  present,  we  may  generally  distinguish  in  them 
two  elementary  parts ; — a  cortical  or  investing  substance,  of  a  fibrous 
horny  texture  ;  and  a  medullary  or  pith-like  substance,  occupying 
the  interior.  In  some  instances,  however,  there  is  scarcely  any  me- 
dullary substance  to  be  traced  ;  whilst  in  other  cases  (as  in  the  hair 
of  the  Musk-Deer)  the  entire  hair  seems  made  up  of  it. 

329.  The  fullest  development  of  both  substances  is  to  be  found  in 
the  spiny  hairs  of  the  Hedgehog,  and  in  the  quills  of  the  Porcupine, 
which  are  but  hairs  on  a  magnified  scale.  The  cortical  substance 
forms  a  dense  horny  tube,  to  which  the  firmness  of  the  structure  seems 
chiefly  due  ;  whilst  the  medullary  substance  is  composed  of  an  aggre- 
gation of  very  large  cells,  which  seem  not  to  possess  any  fluid  con- 
tents in  the  part  of  the  hair  that  is  completely  formed.  In  the  hair  of 
the  Mouse  and  other  small  Rodents,  we  see  the  horny  tube  crossed 
at  intervals  by  partitions,  which  are  sometimes  complete,  sometimes 
only  partial ;  these  are  the  walls  of  the  single  or  double  line  of  cells, 
of  which  the  medullary  substance  is  made  up.     In  the  Human  hair, 


202  STRUCTURE  AND  DEVELOPMENT  OF  HAIR. 

the  chief  part  is  composed  of  a  tube  of  a  horny  substance,  correspond- 
ing with  the  cortical  sheath  of  the  hairs  of  other  animals ;  this  is 
fibrous  in  its  texture,  as  may  be  shown  by  crushing  the  hair,  after  it 
has  been  softened  by  maceration  in  dilute  acid ;  and  the  outlines  of 
the  fibres  are  indicated  by  very  delicate  longitudinal  striae,  which 
may  be  traced  through  its  whole  thickness.  This  fibrous  structure 
sometimes  makes  up  the  whole  thickness  of  the  hair ;  but  there  is 
usually  a  central  medulla,  composed  of  colourless  cells,  with  which 
pigment-cells  are  mingled.  The  hair  is  invested  by  a  series  of  very 
minute  scales,  resembling  those  of  the  epidermis,  but  much  smaller; 
these  are  arranged  in  rows,  like  tiles  upon  a  roof,  and  their  edges 
form  delicate  lines  upon  the  surface  of  the  hair,  which  are  sometimes 
transverse,  sometimes  oblique,  sometimes  apparently  spiral.  The 
colouring  matter  of  the  hair  appears  to  be  related  to  Haematosine ;  it 
is  bleached  by  Chlorine  ;  and  its  hue  seems  dependent  in  part  upon 
the  presence  of  iron,  which  is  found  in  larger  proportion  in  dark  than 
in  light  hair. 

330.  The  fibres  of  the  cortical  substance  are  probably  cells,  which 
have  become  elongated  by  the  process  formerly  described,  and  which 
have  at  the  same  time  secreted  horny  matter  into  their  interior.  This 
change  is  continually  going  on  in  the  bulb  of  the  hair,  at  the  base  of 
the  part  previously  completed  ;  and  by  the  progressive  formation  of 
new  cells  in  the  bulb,  a  constant  growth  of  the  cortical  substance  is 
provided  for.  The  mode  in  which  the  medullary  substance  is  gene- 
rated, does  not  seem  very  clear ;  but  it  probably  consists  of  the  con- 
tents of  the  cells  of  the  pulp,  in  which  a  continuous  growth  goes  on, 
at  the  same  rate  with  that  of  the  bulb.  Thus  the  Hair  is  constantly 
undergoing  elongation  by  the  addition  of  new  substance  at  its  base; 
precisely  in  the  same  manner  as  the  teeth  of  certain  Mammals  grow 
from  persistent  pulps.  The  part  once  formed  usually  undergoes  no 
subsequent  alteration ;  but  there  is  evidence  that  it  may  be  affected 
by  changes  at  its  base,  the  effect  of  which  is  propagated  along  its 
whole  extent.  Thus  it  is  well  known  that  cases  are  not  unfrequent, 
in  which,  under  the  influence  of  strong  mental  emotion,  the  whole  of 
the  hair  has  been  turned  to  gray,  or  even  to  a  silvery  white,  in  the 
course  of  a  single  night ; — a  change  which  can  scarcely  be  accounted 
for  in  any  other  way,  than  by  supposing  that  a  fluid,  capable  of  che- 
mically affecting  the  colour,  is  secreted  at  the  base  of  the  hair,  and 
transmitted  by  imbibition  through  the  medullary  substance  to  the 
opposite  extremity.  The  knowledge  of  the  organized  structure  of 
hair,  enables  us  better  to  understand  some  of  the  effects  of  disease ; 
and  especially  of  that  peculiar  affection  termed  Plica  Polonica.  The 
hair  of  individuals  suffering  from  it  is  disposed  to  split  into  fibres, 
often  at  a  considerable  distance  from  the  roots,  and  to  exude  a  glu- 
tinous substance ;  and  these  two  causes  unite  in  occasioning  that 
peculiar  matting  of  the  hair,  which  has  given  origin  to  the  name  of 
the  disease.  In  the  hair  thus  affected,  there  is  evidently  a  power 
of  transmitting  fluid  absorbed  at  the  roots;  and  it  is  said  that  even 


OF  CELLS  COALESCED  INTO  TUBES.  203 

blood  exudes  from  the  stumps,  when  the  hairs  are  cut  off  close  to  the 
skin. 

6.   Of  Cells  coalesced  into  Tubes ^  with  Secondary  Deposit, 

331.  Most  of  the  tissues  which  have  been  hitherto  described,  differ 
in  no  essentiaLparticulars  from  those  of  Plants;  the  chief  departure 
from  the  forms  presented  by  the  latter,  being  in  the  Fibrous  tissues, 
which,  as  already  observed,  are  introduced  for  the  sake  of  facilitating 
the  movements  of  the  several  parts  of  the  structure,  one  upon  the 
other.  The  various  cellular  tissues  find  their  exact  representatives 
in  those  of  the  Vegetable  fabric ;  and  the  denser  parts  of  the  Animal, 
such  as  Bone,  Cartilage,  &c.,  are  represented  by  the  solid  substances 
formed  by  the  Plant  in  the  heart-wood  of  the  stem,  the  stone  of  fruits, 
&c., — these  substances  acquiring  their  density  in  precisely  the  same 
manner  with  the  Osseous  tissues,  by  the  secreting  action  of  their  own 
cells,  which  draw  a  solidifying  material  from  the  general  circulating 
fluid.  But  we  now  come  to  two  tissues  of  the  highest  importance  in 
the  Animal  fabric ;  the  presence  of  which  is,  indeed,  its  distinguishing 
characteristic.  These  are  the  Muscular,  and  the  J^ervous  tissues. 
The  former  is  the  one,  by  which  all  the  sensible  movements  of  the 
body  are  effected  ;  and  the  latter  serves  as  the  instrument,  by  which 
sensations  are  received,  and  by  which  the  will  excites  the  muscles  to 
action, — besides  serving  as  the  medium  for  other  operations,  in  which 
motion  is  produced,  without  the  intervention  of  either  sensation  or 
will.  These  tissues,  with  the  apparatus  of  bones  and  joints  on  which 
the  muscles  act,  constitute  the  purely  animal  portion  of  the  fabric ; 
and  if  a  being  could  be  constructed,  in  which  they  should  befiapable 
of  continued  activity  without  any  other  assistance,  it  would  be  in  all 
essential  particulars  an  Animal.  But,  as  we  shall  presently  see,  the 
plans  on  which  these  tissues  are  formed,  in  fact  the  very  conditions 
of  their  existence  and  activity,  are  such,  that  they  require  constant 
nutrition  and  re-formation;  so  that  the  Animal  cannot  exist,  without 
an  apparatus  for  preparing,  circulating,  and  maintaining  in  constant 
purity,  a  fluid,  by  which  nutrient  operations  may  be  effected,  and 
which  shall  also  be  the  means  of  carrying  off  the  products  of  the  waste 
consequent  upon  the  action  of  those  tissues.  This  apparatus  consti- 
tutes the  Vegetative  portion  of  the  frame  ;  the  elementary  parts  con- 
cerned in  which  have  been  already  noticed. 

332.  When  we  examine  an  ordinary  Muscle  with  the  naked  eye, 
we  observe  that  it  is  made  up  of  a  number  oi  fasciculi  or  bundles  of 
fibres ;  which  are  arranged  side  by  side  with  great  regularity,  in  the 
direction  in  which  the  muscle  is  to  act ;  and  which  are  united  by 
areolar  tissue.  These  fasciculi  may  be  separated  into  smaller  parts, 
which  appear  like  simple  fibres ;  but  when  these  are  examined  by 
the  microscope,  they  are  found  to  be  themselves  fasciculi  composed  of 
minuter  fibres  bound  together  by  delicate  filaments  of  areolar  tissue. 
By  carefully  separating  these,  w^e  may  obtain  the  ultimate  Muscular 


204 


STRUCTURE  OF  MUSCULAR  FIBRE. 


Fig.  54. 


Fasciculus 
striated  Muscular 
Fibre,  showing  at 
a  the  transverse 
striae,  and  at  b,  the 
longitudinal  striae, 
more  distinctly. 


Fig.  55. 


Fibre.  This  fibre  exists  under  two  forms,  the  striated  and  the  no»- 
striated;  the  former  makes  up  the  whole  substance  of 
those  muscles,  over  which  the  will  has  control,  or 
which  are  usually  called  into  operation  through  the 
nerves ;  whilst  the  latter  exists  in  the  muscles  which 
the  will  cannot  influence,  and  which  are  excited  to 
contraction  by  stimuli  that  act  directly  upon  them. 
The  muscles  of  the  former  class  minister  to  the  ani- 
mal functions ;  those  of  the  latter  to  the  functions  of 
organic  or  vegetative  life.  The  appearance  presented 
by  the  striated  fibres  of  voluntary  muscles,  is  shown 
in  Fig.  54  ;  that  of  the  non-striated  fibres  of  the  mus- 
cles of  organic  life,  in  Fig.  55. 

333.  When  the  fibre  of  voluntary  muscle  is  more 
closely  examined,  it  is  seen  to  consist  of  a  delicate 
tubular  sheath,  quite  distinct  on  the  one  hand  from 
the  areolar  tissue  which  binds  the  fibres  into  fasciculi, 
and  equally  distinct  from  the  internal  substance  of  the 
fibre.  This  cannot  always  be  brought  into  view,  on 
account  of  its  transparency  ;  it  becomes  most  evident,  when  (as  oc- 
casionally happens)  the  contents  of  the  fibre  are  separated  transversely 

by  the  drawing  apart  of  its  extremities, 
without  the  rupture  of  the  sheath ;  but  it 
may  also  be  sometimes  seen  rising  up  in 
wrinkles  upon  the  surface  of  the  fibre,  when 
the  latter  is  in  a  state  of  contraction.  This 
membranous  tube,  which  has  been  termed 
the  Myolemma,  has  nothing  to  do  with  the 
production  of  the  striae ;  these  being  due, 
as  will  be  presently  shown,  to  the  peculiar 
arrangement  of  its  contents.  It  is  not  per- 
forated either  by  nerves  or  capillary  vessels  ; 
and  forms,  in  fact,  a  complete  barrier  be- 
tween the  real  elements  of  Muscular  struc- 
ture, and  the  surrounding  parts.  That  it 
has  no  share  in  the  contraction  of  the  fibre, 
is  evident  from  the  fact  just  mentioned,  in 
regard  to  its  wrinkled  aspect  when  the  fibre 
is  shortened. 

334.  Although  Muscular  fibres  are  com- 
monly described  as  cylindrical  in  form,  yet 
they  are  in  reality  rather  polygonal,  their 
sides  being  flattened  against  those  of  the 
adjoining  fibres.  In  some  instances,  the  angles  are  sharp  and  decided; 
in  others  they  are  rounded  oflf,  so  as  to  leave  spaces  between  the  con- 
tiguous fibres,  for  the  passage  of  vessels.  In  Insects,  the  fibres  often 
present  the  form  of  flattened  bands,  on  which  the  transverse  striae  are 
very  beautifully  marked.     The  size  of  the  fibres  is  subject  to  great 


Non-striated  Muscular  Fibre ;  at 
b,  in  its  natural  state ;  at  a,  show- 
ing the  nuclei  after  the  action  of 
acetic  acid. 


STRIATED  MUSCULAR  FIBRE. 


205 


Tariation,  not  merely  in  different  classes  of  animals,  but  in  different 
species,  in  different  sexes  of  the  same  species,  and  even  in  different 
parts  of  the  same  muscle.  Thus  Mr.  Bowman  estimates  the  average 
diameter  of  the  fibres  in  the  Human  male  at  l-352d  of  an  inch ;  the 
largest  being  l-192d,  and  the  smallest  l-507th.  In  the  female,  he 
found  the  average  to  be  1 -454th  of  an  inch  ;  whilst  the  largest  was 
l-384th,  and  the  smallest  1-6 15th.  The  average  size  of  the  Mus- 
cular fibre  is  greater  among  Reptiles  and  Fishes,  than  in  other  Verte- 
brata ;  but  on  the  other  hand  the  extremes  are  much  wider.  Thus 
its  dimensions  vary  in  the  Frog  from  1-lOOth  to  1-lOOOth  of  an  inch  ; 
and  in  the  Skate  from  l-65th  to  l-300th. 

335.  When  the  striated  Muscular  Fibre  is  examined  still  more 
closely,  it  is  found  to  contain  an  assemblage  of  very  minute  elements, 
which  appear  to  be  flattened  disk-like  cells,  of  very  uniform  size. 
These  primitive  particles  are  adherent  to  each  other  both  by  their  flat 
surfaces,  and  by  their  edges.  The  former  adhesion  is  usually  the 
most  powerful ;  and  causes 

the  substance  of  the  fibre,  Fig.  56. 

when  it  is  broken  up,  to 
present  itself  in  the  form 
of  delicate  Jihrillse,  each  of 
which  is  composed  of  a 
single  row  of  the  primitive 
particles  (Fig.  56).  On  the 
other  hand,  the  lateral  ad- 
hesion is  sometimes  the 
stronger ;  and  causes  the 
fibre  to  break  across  into 
disks,  each  of  which  is  composed  of  a  layer  of  the  primitive  particles 
(Fig.  57).  That  the  fibre  is  a  solid  collection  of  these  elementary 
parts,  and  not  hollow  in  the  centre,  as  some  have  supposed,  is  shown 
by  making  a  thin  transverse  section  of  a  fasciculus  (Fig.  58) ;  by 
which  also  the  polygonal  form  of  the  fibre  is  made  apparent. 


Striated  Muscular  fibre  separating  into  fibrillae,  from  a 
preparation  by  Mr.  Lealand. 


Fig.  67. 


Fig.  58. 


An  ultimate  fibre,  in  which  the  transverse 
splitting  into  disks,  in  the  direction  of  the 
striatiou  of  the  ultimate  fibrils,  is  seen. 


Transverse  section  of  ultimate  fibres 
of  the  biceps.  In  this  figure  the  poly- 
gonal form  of  the  fibres  is  seen,  and 
their  composition  of  ultimate  fibrils. 


206 


STRIATED  MUSCULAR    FIBRE. 


Fig.  39. 


336.  When  the  fibrillse  are  separately  examined,  under  a  high  mag- 
nifying power,  they  are  seen  to  present  a  cylindrical  or  slightly-beaded 
form,  and  to  be  made  up  of  a  linear  aggregation  of  distinct  cells.  We 
observe  the  same  alternation  of  light  and   dark  spaces,  as  when  the 
fibrillae  are  united  into  fibres  or  into  small  bundles;  but  it  may  be 
distinctly  seen,  that  each  light  space  is  divided  by  a  transverse  line ; 
and  that  there  is  a  pellucid  border  at  the  sides  of  the  dark  spaces,  as 
well  as  between  their  contiguous  extremities  (Fig.  59).  This  pellucid 
border  seems  to  be  the  cell-wall ;  the  dark  space  enclosed  by  it  (which 
is  usually  bright  in  the  centre)  being  the  cavity  of  the  cell,  which  is 
filled  with  a  highly-refracting  substance.     When  the  fibril  is  in  a 
state  of  relaxation,  as  seen  at  a,  the  diameter  of  the 
cells  is   greatest  in   the   longitudinal  direction  :   but 
when  it  is  contracted,  the  fibril  increases  in  diameter 
as  it  diminishes  in  length  ;  so  that  the  transverse  dia- 
meter of  each  cell  becomes  equal  to  the  longitudinal 
diameter,  as  seen  at  b;  or  even  exceeds  it.     Thus  the 
act  of  Muscular  contraction  seems  to    consist  in  a 
change  of  form  in  the  cells  of  the   ultimate  fibrillae, 
consequent  upon  an  attraction  between  the  w^alls  of 
their  two  extremities ;  and  it  is  interesting  to  observe, 
how  very  closely  it  thus  corresponds  with  the  contrac- 
tion of  certain  Vegetable  tissues,  of  which  the  com- 
ponent cells  (§  345)  appear  to  produce  a  movement, 
when  they  are  irritated,  by  means  of  a  similar  change 
of  form.     The  essential  difference,  therefore,  between 
the  muscular  tissue  of  Animals,  and  the   contractile 
tissues  of  Plants,   consists  in   the  subjection   of  the 
former  to  nervous  influence  (§  353).     The   diameter 
of  the  ultimate  fibrilltB  will   of  course  be  subject  to 
variations,  in  accordance  with  their  contracted  or  re- 
laxed condition  ;  but  seems  to  be  otherwise  tolerably 
uniform  in  different  animals,  being  for  the  most  part 
about  1-I0,000th  of  an  inch.     It  has  been  observed, 
however,  as  high  as  l-5000th  of  an  inch,  and  as  low 
as  l-20,000th,  even  when  not  put  upon  the  stretch. 
The  average  distance  of  the  stricE,  too,  is  nearly  uniform  in  different 
animals ;  though  considerable  variations  present  themselves  in  every 
individual,  and  in  different  parts  of  the   same  muscle.     Thus  the 
maximum  distance  varies  in  different  animals  from   1- 15,000th   to 
l-20,000th  of  an  inch  ;  the  minimum  from  l-7500th  to  i-4500th  of 
an  inch  ;  while  the  mean  does  not  depart  widely  in  any  instance  from 
l-10,000th. 

337.  The  Muscular  fibre  of  Organic  Life  is  very  different  from  that 
which  has  been  now  described.  It  consists  of  a  series  of  filaments, 
which  do  not  present  transverse  markings;  but  which  are  tubular  like 
the  preceding,  their  contents  having  a  granular  consistence,  without 


I 

B 

e 

1 

■ 

1 

B 

1 

m 

i 

m 
i 

i 

B 

i 

m 

1 

il 

Structure  of  the 
ultimate  fibrillae 
of  striated  muscu- 
lar fibre  :— a,  a  fi- 
bril in  a  state  of 
ordinary  relaxa- 
tion ;  h,  a  fibril  in 
a  state  of  partial 
contraction. 


NON-STRIATED   MUSCULAR   FIBRE. 


207 


A.  A  muscular  fibre  of 
organic  life  from  the  uri- 
nary bladder,  magnified 
600  times,  linear  measure. 
Two  of  the  nuclei  are 
seen. 

B.  A  muscular  fibre  of 
organic  life,  from  the  sto- 
mach, mjignified  600  times. 
The  diameter  of  this  and 
of  the  preceding  fibre,  mid- 
way between  the  nuclei, 
•was  l-4750ih  of  an  inch. 


any  definite  arrangement  of  the  particles  into  disks  or  fibrillse.  Their 
size  is  usually  much  less  than  that  of  the  striated 
muscular  fibre ;  but  owing  to  the  extreme  varia- 
tion in  the  degree  of  flattening  which  they  undergo, 
it  is  difficult  to  make  even  an  average  estimate  of 
their  dimensions.  Those  of  the  alimentary  canal 
of  Man  are  stated  by  Dr.  Baly  to  measure  from 
about  the  l-2500th  to  the  l-5600th  part  of  an  inch 
in  diameter.  They  generally  present  nodosities  or 
enlargements  at  frequent  intervals  (Fig.  60) ;  the 
character  of  which  will  be  presently  apparent. 
These  fibres  are,  like  those  of  the  other  muscles, 
arranged  in  a  parallel  manner  into  bands  or  fasci- 
culi ;  but  these  fasciculi  are  generally  interwoven 
into  a  network,  without  having  any  fixed  points  of 
attachment.  It  is  of  this  kind  of  structure,  that 
the  proper  muscular  coat  of  the  oesophagus,  of  the 
stomach  and  intestinal  canal,  and  of  the  bladder, 
is  composed ;  it  makes  up,  also,  the  substance  of 
the  pregnant  uterus :  and  it  is  found  in  no  incon- 
siderable amount  in  the  trachea  and  bronchial 
tubes.  The  fibres  of  the  uterus  somewhat  diffier  in 
their  aspect  from  those  of  other  parts;  being  much  broader  at  their 
centre,  and  tapering  off  towards  their  extremities.  In  the  Heart,  a 
mixture  of  the  striated  and  non-striated  fibres  is  found  ;  a  modification 
of  the  latter  form  of  tissue  exists  in  the  middle  coat  of  the  arteries, 
especially  in  the  smaller  branches;  and  fibres  of  the  same  kind  are 
interwoven  wdth  the  other  fibrous  tissues  in  the  substance  of  the  skin, 
and  especially  in  the  dartos,  giving  it  a  contractility  which  is  mani- 
fested under  the  influence  of  cold  or  of  mental  emotions,  and  thus 
producing  that  general  roughness  and  rigidity  of  the  surface,  which  are 
known  as  cutis  anserina,  and  throwing  the  scrotum  into  wrinkles. 

338.  From  the  study  of  the  early  development  of  Muscular  Fibre, 
it  appears  that  the  Myolemma,  or  external  transparent  tube,  is  the 
part  first  formed ;  this  being  distinctly  visible,  long  before  any  traces 
of  fibrillae  can  be  observed  in  it.  This  tube  takes  origin,  like  the 
straight  ducts  of  Plants,  in  cells  laid  end  to  end  ;  the  cavities  of 
which  coalesce,  by  the  disappearance  of  the  partitions,  at  a  subse- 
quent period.  The  nuclei  of  these  original  cells  may  be  distinctly 
seen,  for  some  time  after  the  appearance  of  the  transverse  striae,  which 
indicate  the  formation  of  the  fibrillae  in  their  interior ;  and  they  pro- 
ject considerably  from  the  sides  of  the  fibres.  In  the  fully-formed 
muscle  of  animal  life,  however,  they  are  not  perceptible,  except  when 
the  fibre  is  treated  with  weak  acid;  the  effect  of  w^hich  is  to  render 
the  nuclei  more  opaque,  whilst  the  surrounding  structure  becomes 
more  transparent.  They  are  usually  numerous  in  proportion  to  the 
size  of  the  fibre.  There  is  every  probability  that  these  nuclei  con- 
tinue to  act,  like  the  "  germinal  spots"  of  the  glandular  follicles,  as 


208 


DEVELOPMENT  AND  GROWTH  OF  MUSCULAR  FIBRE. 


Fig  61. 


Mass  of  ultimate  fibres  from  the 
pectoralis  major  of  the  human 
foetus,  at  nine  months.  Thtse 
fibres  have  been  immersed  in  a 
solution  of  tartaric  acid,  and  their 
"numerous  corpuscles,  turned  in 
various  directions,  some  present- 
ing nucleoli,"  are  shown. 


centres  of  nutrition ;  from  which  the  minute  cells  that  compose  the 
fibrillae  are  developed  as  they  are  required.  The  diameter  of  the 
Muscular  Fibre  of  the  foetus  is  not  above 
one-third  of  that  which  it  possesses  in  the 
adult;  and  as  the  size  of  the  ultimate  par- 
ticles is  the  same  in  both  cases,  their  number 
must  be  greatly  multiplied  during  the  growth 
of  the  structure.  But  we  shall  find  reason 
to  believe,  that  the  decay  of  these  particles 
is  constantly  taking  place,  with  a  rapidity 
proportional  to  the  functional  activity  of  the 
Muscle ;  and  their  generation,  which  occurs 
as  continually,  when  the  nutrient  operations 
proceed  in  their  regular  course,  is  proba- 
bly accomplished  by  a  development  from 
these  centres,  at  the  expense  of  the  blood 
with  which  the  Muscle  is  copiously  sup- 
plied. 

339.  From  the  preceding  history  it  appears,  that  there  is  no  dif- 
ference, at  an  early  stage  of  development,  between  the  striated  and 
the  non-striated  forms  of  muscular  fibre.  Both  are  simple  tubes, 
containing  a  granular  matter  in  which  no  definite  arrangement  can  be 
traced,  and  presenting  enlargements  occasioned  by  the  presence  of 
the  nuclei.  But  whilst  the  striated  fibre  goes  on  in  its  development, 
until  the  fibrillae,  with  their  alternation  of  light  and  dark  spaces,  are 
fully  produced,  the  non-striated  fibre  retains  throughout  life  its  ori- 
ginal embryonic  condition. 

340.  We  have  seen  that  the  Muscular  tissue,  properly  so  called, 
is  as  extra-vascular  as  cartilage  or  dentine ;  for  its  fibres  are  not 
penetrated  by  vessels  ;  and  the  nutriment  required  for  the  growth  of 
its  contained  matter  is  drawn  by  absorption  through  the  myolemma. 

But  the  substance  of  Muscle  is  extremely 
vascular ;  the  capillary  vessels  being  dis- 
tributed in  nearly  parallel  lines,  in  the 
minute  interspaces  between  the  fibres; 
so  that  it  is  probable  that  there  is  no 
fibre,  which  is  not  in  close  relation  with 
a  capillary.  Hence  there  is  every  pro- 
vision for  the  active  nutrition  of  this 
tissue;  the  arterial  circulation  bringing 
the  materials  for  its  growth  and  renova- 
tion ;  whilst  the  venous  conveys  away 
the  products  of  the  waste  or  disintegration,  which  is  consequent  upon 
its  active  exercise.  The  supply  of  blood  is  not  merely  requisite  for 
the  nutrition  of  the  muscular  tissue ;  but  it  also  affords  a  condition 
which  is  requisite  for  its  action.  This  condition  is  oxygen.  It  is  not 
enough  that  blood  should  circulate  through  the  muscles;  for  that 
blood,  to  exercise  any  beneficial  influence,  must  be   arterialized. 


Capillary  network  of  Muscle. 


NUTRITION  AND  COMPOSITION  OF  MUSCLE.  209 

Consequently  the  muscles  of  warm-blooded  animals  soon  lose  their 
contractile  power,  after  the  supply  of  arterial  blood  has  been  sus- 
pended, either  by  the  cessation  of  the  circulation,  or  by  the  want  of 
aeration  of  the  blood ;  but  those  of  cold-blooded  animals  preserve 
their  properties  for  a  much  longer  period,  in  accordance  with  the 
general  principle  formerly  stated, — that,  the  lower  the  usual  amount 
of  vital  energy,  the  longer  is  its  persistence,  after  the  withdrawal  of 
the  conditions  on  which  it  is  dependent. 

341.  The  Muscles  of  Animal  Life  are,  of  all  the  tissues  except  the 
Skin,  the  most  copiously  supplied  with  Nerves.  These,  like  the  blood- 
vessels, lie  on  the  outside  of  the  Myolemma  of  each  fibre  ;  and  their 
influence  must  consequently  be  exerted  through  it.  The  arrangement 
of  these  nerves  is  shown  in  the  succeeding  figure.  Their  ultimate 
fibres  or  tubes  cannot  be  said  to  terminate  anywhere  in  the  muscular 
substance ;  for  after  issuing  from  the  trunks,  they  form  a  series  of 
loops,  which  either  return  to  the  same  trunk,  or  join  an  adjacent  one. 
The  occasional  appearance  of  a  termination  to  a  nervous  fibril  is 
caused  by  its  dipping-down  between  the  muscular  fibres,  to  pass 
towards  another  stratum. — The  non-striated  muscles,  however,  are 
very  sparingly  supplied  with  nerves  ;  and  these  are  derived, — for  the 
most  part,  if  not  entirely, — from  the  Sympathetic  system,  rather  than 
from  the  Cerebro-spinal. 

342.  Every  Muscular  Fibre,  of  the  striated  kind  at  least,  is  at- 
tached at  its  extremities  to  fibrous  tissue ;  through  the  medium  of 
which  it  exerts  its  contractile  power  on  the  bone  or  other  substance, 
which  it  is  destined  to  move.  The  muscular  fibre  usually  ends  ab- 
ruptly by  a  perfect  disk  ;  and  the  myolemma  seems  to  terminate  there. 
The  tendinous  fibres  are  attached  to  the  whole  surface  of  the  disk ; 

Fig.  63. 


Portion  of  muscle,  showing  the  arrangement  of  the  motor  nerves  supplying  it. 

and  probably  become  continuous  with  the  myolemma.     Thus  the- 
whole  muscle  is  penetrated  by  minute  fasciculi  of  tendinous  fibres  ; 
and  these  collect  at  its  extremities  into  a  tendon.     Sometimes  the 
14 


210  CONTRACTILITY  OF  VEGETABLE  TISSUES. 

muscular  fibres  are  attached  obliquely  to  the  tendon,  which  forms  a 
broad  band  that  does  not  subdivide;  this  is  seen  in  the  legs  of  Insects 
and  Crustacea,  in  which  the  muscular  fibres  have  what  is  called  a 
joenwi/brm  arrangement,  being  inserted  into  the  tendon,  on  either  side, 
like  the  laminse  of  a  feather  into  its  stem. — The  forms  which  diflferent 
muscles  present,  have  reference  purely  to  the  mechanical  purposes, 
which  they  have  respectively  to  accomplish.  The  elements  are  the 
same  in  all,  both  as  regards  structure  and  properties. 

343.  Notwithstanding  the  energy  of  growth  in  Muscular  tissue,  it 
is  doubtful  if  it  is  ever  regenerated,  when  there  has  been  actual  loss 
of  substance.  Wounds  of  muscles  are  united  by  Areolar  Tissue, 
which  gradually  becomes  condensed;  but  its  fibres  never  acquire 
any  degree  of  contractility. 

344.  It  is  probable  that  the  pure  Muscular  Fibre  is  identical  in 
Chemical  composition, — or  nearly  so, — with  the  Fibrin  of  the  blood. 
It  is,  however,  impossible  to  separate  it  completely  from  the  areolar 
tissue,  nerves,  blood-vessels,  fatty  matter,  &c.,  which  enter  into  the 
substance  of  the  muscle  ;  so  that  it  cannot  be  precisely  analyzed.  In 
ordinary  muscle,  the  solid  matter  forms  about  23  parts  in  100  ;  the 
remainder  consisting  of  water. — The  solid  matter  contains  about  7^ 
per  cent,  of  fixed  salts. 

345.  We  now  come  to  investigate  the  remarkable  property,  which 
is  the  distinguishing  characteristic  of  Muscular  tissue; — that  of  con- 
tracting on  the  application  of  a  stimulus.  Some  approaches  to  this 
property  are  manifested  by  certain  Vegetable  structures.  Thus,  if 
the  small  enlargement  at  the  base  of  the  footstalk  of  the  leaf  of  the 
Sensitive  Plant,  be  touched  ever  so  slightly,  the  leaf  will  be  imme- 
diately drawn  down  by  the  contraction  of  the  tissue  of  the  part 
irritated.  If  the  leaf  itself  be  touched,  the  same  effect  results,  but 
apparently  through  a  different  channel ;  the  tissue  of  the  leaf  contracts 
where  it  is  touched,  and  forces  some  of  its  fluid  along  the  vessels  of 
the  footstalk  into  the  upper  side  of  the  little  excrescence  at  its  base, 
by  the  distension  of  which  the  leaf  is  forced  down.  In  the  IHoncea 
muscipula,  or  Venus's  Fly-trap,  there  is  a  similar  transmission  of  the 
effect  of  the  stimulus  from  one  part  to  another ;  for  the  two  lobes  of 
the  leaf,  which  form  the  trap,  are  made  to  close  together,  when  an 
insect  settles  upon  either  one  of  three  spines  which  project  from  the 
surface  of  each  lobe,  or  when  the  points  of  these  spines  are  touched 
with  any  hard  body.  Many  other  instances  of  Vegetable  movement 
might  be  brought  together.  Some  of  them  are  obviously  produced 
by  an  enlargement  or  contraction  of  the  cells,  occasioned  by  variations 
in  the  amount  of  fluid  they  contain  ;  and  these  variations  depend  upon 
the  hygrometric  state  of  the  atmosphere.  With  these  we  have  nothing 
to  do.  But  there  are  many,  in  which  (as  in  the  case  of  the  Sensitive- 
plant  first  mentioned)  a  stimulus  applied  to  a  part  occasions  the  imme- 
diate contraction  of  its  cells,  and  a  consequent  motion  in  the  same 
part.  And  there  are  also  several,  in  which  the  contraction  produces 
motion  in  a  distant  part,  as  in  the  Dionaea;  but  this  propagation 


INHERENT  CONTRACTILITY  OF  MUSCULAR  FIBRE.  211 

appears  to  be  of  a  simply  mechanical  character ;  being  accomplished 
through  the  medium  of  fluid,  which  is  forced  from  one  part  by  its  own 
contraction,  and  caused  to  distend  another. 

346.  From  these  examples,  however,  it  is  evident  that  the  property 
of  contractility  is  not  entirely  restricted  to  the  Animal  kingdom ;  and 
we  shall  find  that  the  simplest  form  under  which  it  manifests  itself  in 
the  Animal  body,  bears  a  close  relationship  with  that  which  is  dis- 
played in  Plants.  The  non-striated  fibre  of  the  alimentary  canal, 
which  is  subservient  to  the  functions  of  Vegetative  life  alone,  is  called 
into  action  much  more  readily  by  a  stimulus  directly  applied  to  itself, 
than  it  is  in  any  other  mode.  Such  is  not  the  case,  however,  with 
the  striated  fibre,  of  which  the  muscles  of  Animal  life  are  composed ; 
this  being  much  more  readily  called  into  action  by  a  peculiar  stimulus 
conveyed  through  the  nerves  supplying  those  muscles,  than  in  any 
other  more  directly  applied  to  them. 

347.  The  Contractility  of  Muscular  Fibre  shows  itself  under  two 
forms.  Its  most  obvious  and  striking  manifestations  are  those  that 
occur  in  the  voluntary  muscles  and  in  the  heart ;  which,  when  in 
action,  exhibit  powerful  contractions  alternating  with  relaxations.  The 
property  w^hich  is  concerned  in  these  is  distinguished  as  Irritability. 
On  the  other  hand,  we  find  that  these  same  muscles  exhibit  a  tend- 
ency to  a  moderate  and  permanent  contraction,  which  is  not  shown 
by  them  when  they  are  dead,  and  which  cannot,  therefore,  be  the 
result  of  elasticity  or  of  any  simple  physical  property ;  this  endow- 
ment, which  seems  to  exist  in  the  greatest  amount  in  certain  forms  of 
the  non-striated  fibre,  is  called  Tonicity. 

348.  That  the  irritability  of  Muscles  is  a  property  inherent  in  them, 
and  in  this  respect  analogous  to  the  peculiar  vital  endowments  of  any- 
other  forms  of  tissue,  cannot  be  any  longer  a  matter  of  doubt ; — though 
many  Physiologists  have  sought  to  show,  that  it  is  in  some  way 
derived  from  the  nerves.  Not  only  may  an  entire  Muscle  be  made 
to  contract,  by  the  application  of  a  proper  stimulus,  long  after  the 
division  of  the  nervous  trunks  supplying  it;  but  even  a  single  fibre, 
completely  isolated  from  all  its  nervous  connections,  may  be  seen  to 
contract  under  the  Microscope.  Moreover,  in  the  non-striated  mus- 
cular fibre,  it  is  often  diflficult  to  excite  contractions  through  the  nerves 
at  all,  when  a  stimulus  directly  applied  to  itself  will  immediately  pro- 
duce sensible  and  vigorous  movements.  The  energy  of  the  contractile 
power  depends  in  great  part  upon  the  state  of  nutrition  of  the  muscle  ; 
and  this  again  is  influenced  by  the  degree  in  which  it  is  exercised. 
Now  as  the  Muscles  of  Animal  Life  are  all  excited  to  action,  in  the 
usual  state  of  things,  through  the  medium  of  their  nerves,  it  follows 
that  if  the  nerves  be  paralyzed,  the  muscles  will  be  seldom  or  never 
called  into  use.  When  disused,  they  will  receive  very  little  nourish- 
ment; the  disintegrating  changes  will  not  be  counterbalanced  by 
reparative  processes ;  and  in  consequence,  the  muscular  structure  will 
be  gradually  so  far  impaired,  as  to  lose  its  peculiar  properties, — and 
will  even,  in  time,  almost  totally  disappear.     Yet  even  after  the 


212  INHERENT  CONTRACTILITY  OF  MUSCULAR  FIBRE. 

almost  complete  departure  of  muscular  contractility,  through  the 
metamorphosis  of  the  structure  consequent  upon  disuse,  it  may  be 
again  recovered,  if  the  muscles  be  called  into  exercise;  but  the 
recovery  of  the  power  is  very  slow,  and  proceeds  pari  passu  with  the 
improvement  in  the  nutrition  of  the  part,  being  more  tedious  in  pro- 
portion to  the  length  of  the  previous  disuse. 

349.  That  the  Irritability  of  Muscular  fibre  belongs  to  itself,  and 
is  not  derived  in  any  way  from  the  nerves,  is  further  shown  in  the 
following  manner.  If  a  set  of  muscles  (as  those  of  the  leg  of  a  Rabbit 
or  Frog)  be  repeatedly  thrown  into  action  by  galvanism,  until  the 
stimulus  will  no  longer  occasion  their  contraction,  their  irritability  is 
then  said  to  be  exhausted  ;  by  rest,  however,  it  is  recovered, — the 
nutritive  processes  making  good  the  loss  previously  suffered.  Now 
it  has  been  shown  by  Dr.  J.  Reid,  that  this  recovery  may  take  place, 
even  after  the  division  of  all  the  nerves  supplying  the  limb  ;  provided 
that  the  nutrition  of  the  part  be  not  interfered  with.  It  has  been 
further  shown  by  the  same  excellent  Physiologist,  that,  if  the  nerves 
of  a  limb  be  divided,  the  loss  or  retention  of  the  contractility  of  the 
muscles  entirely  depends  upon  the  degree  of  exercise  to  which  they 
are  subjected,  and  consequently  upon  the  nutrition  they  receive. 
The  muscles  of  the  hind-leg  of  a  Rabbit,  whose  sciatic  nerve  had 
been  divided,  were  found  to  lose  their  contractility  almost  completely 
in  the  course  of  seven  weeks.  They  were  much  smaller,  paler,  and 
softer,  than  the  corresponding  muscles  of  the  opposite  leg ;  and  they 
scarcely  weighed  more  than  half  as  much  as  the  latter.  Now  when 
the  nerves  of  both  hind-legs  of  a  Frog  were  cut,  and  the  muscles  of 
one  of  the  limbs  thus  paralyzed  were  daily  exercised  by  a  weak  gal- 
vanic battery,  whilst  those  of  the  other  were  allowed  to  remain  at 
rest,  it  was  found  after  the  lapse  of  two  months  that  the  muscles  of 
the  exercised  limb  retained  their  original  size  and  firmness,  and  con- 
tracted vigorously,  whilst  those  of  the  other  had  shrunk  to  one-half 
their  former  size.  Though  the  latter  still  retained  their  contractility, 
there  could  be  no  doubt  that  they  would  soon  lose  it,  in  consequence 
of  the  change  already  far  advanced  in  their  physical  structure  ;  this 
change  not  being  as  rapid  in  cold-blooded  animals,  as  in  Birds  and 
Mammals. 

350.  By  these  and  other  facts,  then,  it  may  be  regarded  as  com- 
pletely proved,  that  the  Irritability  of  Muscles  is  a  vital  endowment, 
belonging  to  them  in  virtue  of  their  peculiar  structure  ; — that,  so  long 
as  this  structure  is  maintained  in  its  normal  condition  by  the  nutritive 
processes,  so  long  is  the  property  capable  of  being  manifested  ; — but 
that  any  cause  which  interferes  with  the  nutrition  of  a  muscle,  impairs 
or  destroys  its  irritability.  No  cause  is  so  effectual  in  doing  this,  as 
complete  disuse;  and  no  means  is  so  sure  to  produce  complete  disuse 
of  a  muscle,  as  the  division  of  its  nerve,  since  its  being  called  into 
exercise  in  any  other  way  is  very  improl3able ;  hence  the  section  of 
the  nerve  is  almost  certain  to  produce,  in  time,  the  loss  of  the  con- 
tractility of  the  muscle.     But  if  a  means  be  devised,  by  which  the 


I 


EFFECTS  OF  STIMULI  ON  MUSCULAR  FIBRE.  213 

muscle  may  still  be  called  into  action  in  any  other  way, — as  in  Dr. 
Reid's  experiment  just  quoted, — its  irritability  is  retained,  because  its 
regular  nutrition  is  continued. 

351.  We  have  now  to  inquire,  then,  into  the  circumstances  under 
which  this  peculiar  endowment  acts ;  or  the  means  by  which  it  may 
be  called  into  operation,  the  mode  in  which  the  contraction  takes 
place,  and  the  conditions  which  are  necessary  for  its  performance. — 
All  Muscular  Fibre,  which  has  not  lost  its  contractility,  may  be  made 
to  contract  by  a  stimulus  applied  directly  to  itself;  and  this  stimulus 
may  be  of  different  kinds.  The  simplest  is  the  contact  of  a  solid  sub- 
stance ;  thus  we  may  excite  muscular  contractions  by  simply  touching 
the  fibre, — ^just  as  we  cause  contraction  in  the  tissue  of  the  Dionsea 
or  Sensitive  Plant.  Most  substances  of  strong  chemical  action,  such 
as  acids  and  alkalies,  will  call  forth  the  contractility  of  muscular  fibre, 
when  applied  to  it ;  and  the  same  result  is  produced  by  heat,  cold, 
and  electricity, — the  last-named  agent  being  the  most  powerful  of 
all.  The  effect  of  the  application  of  any  of  these  stimuli  varies  con- 
siderably, according  to  the  kind  of  Muscle  on  which  it  is  exerted. 
If  we  irritate  a  portion  of  a  muscle  composed  of  striated  fibre  (any 
one  of  the  voluntary  muscles  for  example),  the  fasciculus  of  fibres 
which  is  touched  will  immediately  contract,  and  that  one  only ;  and 
the  contracted  fasciculus  will  soon  relax,  without  communicating  its 
movement  to  any  other. 

352.  If  we  irritate  a  portion  of  non-striated  fibre,  however,  as  that 
of  the  Alimentary  canal,  the  fasciculus  which  is  stimulated  will  con- 
tract less  suddenly,  but  ultimately  to  a  greater  amount ;  its  relation 
will  be  less  speedy ;  and  before  it  takes  place,  other  fasciculi  in  the 
neighbourhood  begin  to  contract;  their  contraction  propagates  itself 
to  others ;  and  so  on.  In  this  manner,  successive  contractions  and 
relaxations  maybe  produced  through  a  considerable  part  of  the  canal, 
by  a  single  prick  with  a  scalpel;  a  sort  of  wave  of  contraction  being 
transmitted  in  the  direction  of  its  length,  and  being  followed  by  relaxa- 
tion. Again,  in  the  Muscular  structure  of  the  Bladder  and  Uterus, 
powerful  contractions  are  excited  by  irritation,  and  these  produce  a 
great  degree  of  shortening ;  but  they  do  not  alternate  in  the  healthy 
state  with  any  rapid  and  decided  elongation ;  whilst,  on  the  other 
hand,  an  irritation  applied  to  one  spot  causes  more  extensive  contrac- 
tions than  are  seen  to  occur  as  its  immediate  consequence  in  the  pre- 
ceding cases.  In  the  Heart,  the  muscular  structure  of  a  large  part  of 
the  organ  is  thrown  into  rapid  and  energetic  contraction,  by  a  stimu- 
lus applied  at  any  one  point ;  and  this  contraction  is  speedily  followed 
by  relaxation.  And  in  the  fibrous  tissue  of  the  middle  coat  of  the 
Arteries,  the  contraction  takes  place  rather  after  the  manner  of  that 
of  the  bladder  and  uterus,  and  a  prolonged  application  of  the  stimulus 
is  often  necessary  to  produce  the  effect ;  but  when  the  contraction 
commences,  it  produces  a  considerable  degree  of  shortening,  which 
takes  place  in  other  fasciculi  than  those  directly  irritated,  and  does  not 
speedily  give  way  to  relaxation. 


214  ACT  OF  MUSCULAR  CONTRACTION. 

353.  On  the  other  hand,  when  the  stimuli  which  excite  muscular 
contraction  are  applied  to  the  nerve,  which  supplies  a  voluntary  mus- 
cle composed  of  striated  fibre,  they  produce  a  simultaneous  contraction 
in  the  whole  muscle;  the  effect  of  the  stimulus  being  at  once  exerted, 
upon  every  part  of  it.  In  the  ordinary  action  of  such  muscles,  the 
nervous  system  is  always  the  channel  through  which  they  are  called 
into  play,  whether  to  carry  into  effect  the  determinations  of  the  mind 
(§  391),  or  to  perform  some  office  necessary  to  the  continuance  of 
life,  such  as  the  movements  concerned  in  Respiration  (§  394).  The 
nerves  of  the  striated  fibre  are  all  derived  at  once  from  the  brain  or 
spinal  cord. — The  ordinary  actions  of  the  non-striated  fibre,  on  the 
contrary,  are  executed  in  respondence  to  stimuli  applied  directly  to 
themselves.  It  is  so  difficult  to  excite  contractions  in  it  through  the 
medium  of  its  nerves,  that  many  Physiologists  have  denied  the  possi- 
bility of  doing  so  ;  and  the  nerves  lose  their  power  of  conveying  the 
influence  of  stimuli  very  soon  after  death,  although  the  contractility 
of  the  muscles  may  remain  for  a  considerable  time.  The  nerves  of 
the  non-striated  fibre  are  chiefly  those  belonging  to  the  Sympathetic 
system;  but,  as  will  be  shown  hereafter  (Chap.  XII.),  those  which 
excite  motion  are  probably  derived  in  reality  from  the  Cerebro-spinal 
system,  through  the  communicating  branches  which  unite  the  two. 

354.  When  a  Muscle  is  thrown  into  contraction,  its  bulk  does  not 
appear  to  be  at  all  affected.  Its  extremities  approach,  so  that  it  is 
shortened  in  the  direction  of  its  fibres;  but  its  diameter  enlarges  in 
the  same  proportion.  It  was  formerly  supposed  that  the  ultimate 
fibreSj^in  the  act  of  contraction,  threw  themselves  into  zigzag  folds; 
but  this  is  now  well  ascertained  not  to  be  the  case.  The  fibre,  like 
the  entire  muscle,  preserves  its  straight  direction  in  shortening,  and 
increases  in  diameter.  The  fibrillse  themselves,  as  already  mentioned 
(§  336)  exhibit  an  evident  change,  in  regard  to  the  distances  of  their 
successive  light  and  dark  portions;  and  the  fibre,  which  is  made  up 
of  these,  exhibits,  in  its  contracted  state,  a  very  close  approximation 
of  the  transverse  striae;  to  such  an  extent  that  they  become  two,  three, 
or  even  four  times  as  numerous  in  a  given  length,  as  they  are  in  a 
similar  length  of  a  non-contracted  fibre.  According  to  Mr.  Bowman's 
observations,  the  contraction  usually  commences  at  the  extremities  of 
a  fibre  ;  but  it  may  occur  also  at  one  or  more  intermediate  points. 
The  first  appearance  of  contraction  is  a  dark  spot,  caused  by  the  ap- 
proximation of  the  strise ;  and  this  gradually  extends  itself,  so  as  to 
involve  a  greater  or  less  proportion  of  the  length  of  the  fibre.  The 
approximation  of  the  solid  portions  forces  out  the  fluid,  which  was 
previously  contained  amongst  the  fibrillse  ;  and  this  is  seen  to  lie  in 
bullse  or  blebs  beneath  the  myolemma,  which  is  drawn  up  into 
wrinkles. 

355.  The  successive  stages  of  the  act  of  contraction  can  only  be 
thus  observed,  when  it  takes  place  very  slowly,  as  in  the  rigor  mortis^ 
or  slow  contraction  after  death,  the  phenomena  of  which  will  be  pre- 
sently noticed.     But  the  resulting  change  in  muscular  fibres,  which 


ACT  AND  CONDITIONS  OF  MUSCULAR  CONTRACTION.  215 

have  been  made  to  contract  by  galvanism  or  any  other  stimulus,  is 
essentially  the  same.  This  may  be  best  seen  in  transparent  Entozoa, 
Crustacea,  and  others  among  the  lower  Articulated  Animals,  whilst 
alive.  Again,  in  persons  who  have  died  from  Tetanus,  a  considerable 
number  of  the  fibres  are  found  to  have  been  ruptured  by  the  violent 
spasmodic  action  ;  the  contractile  force,  called  into  action  by  the  pow- 
erful stimulation  of  the  nerves,  having  overcome  the  tenacity  of  the 
fibre :  and  in  such  cases,  the  same  approximation  of  the  transverse 
striae,  and  proportional  increase  in  the  diameter  of  the  fibre,  are  to  be 
observed. 

356.  It  appears  that,  even  when  considerable  force  of  contraction 
is  being  exerted,  the  whole  fibre  is  seldom  or  never  in  contraction  at 
once;  but  that  a  continual  interchange  is  taking  place  amongst  its 
different  parts, — some  of  them  passing  from  the  contracted  to  the 
relaxed  state,  as  shown  by  the  separation  of  the  transverse  striae, — 
whilst  others  are  taking  up  the  duty,  and  passing  from  the  relaxed  to 
the  contracted  condition,  as  shown  by  the  approximation  of  the  striae. 
But  it  is  not  only  among  the  different  parts  of  the  individual  fibres, 
that  this  interchange  seems  to  take  place.  There  is  good  reason  to 
believe  that,  when  a  muscle  is  kept  in  a  contracted  state,  by  an  effort 
of  the  will,  for  any  length  of  time,  only  a  part  of  its  fibres  are  in  con- 
traction at  any  one  time ;  but  that  a  constant  interchange  of  condition 
takes  place  amongst  them,  some  contracting  whilst  others  are  relaxing, 
so  that  the  entire  muscle  remains  contracted,  whilst  the  state  of  every 
individual  fibre  may  have  undergone  a  succession  of  alterations. 
When  the  ear  is  applied  to  a  muscle  in  vigorous  action,  an  exceed- 
ingly rapid  faint  silvery  vibration  is  heard,  which  seems  to  be  attri- 
butable to  this  constant  movement  in  its  substance. 

357.  Thus  it  appears  that  the  prolongation  of  the  contraction  of  a 
muscle,  through  any  length  of  time,  is  not  opposed  to  the  fact  that,  in 
the  individual  fibres,  relaxation  speedily  follows  contraction ;  but  is 
only  a  peculiar  manifestation  of  it.  The  ordinary  movements  of  the 
Heart  exhibit  a  different  manifestation  ;  its  fibres  contracting  simulta- 
neously, and  relaxing  together,  instead  of  alternating  amongst  them- 
selves like  those  of  a  voluntary  muscle. — The  occasional  zigzag 
arrangement  of  the  fibres,  which  has  been  supposed  to  be  their  con- 
tracted state,  is  really  dependent  upon  the  approximation  of  their 
extremities,  in  consequence  of  the  contraction  of  some  neighbouring 
fibres,  whilst  their  own  condition  is  that  of  relaxation.  It  may  be 
artificially  produced  by  bringing  together  the  two  extremities  of  a 
fasciculus,  after  the  irritability  of  the  fibre  has  ceased ;  so  that  the 
flexure  at  determinate  points  must  be  owing  simply  to  the  physical 
arrangement  of  the  parts, — perhaps  to  the  passage  of  nerves  or  ves- 
sels in  a  transverse  direction. 

358.  We  have  now  to  consider  the  conditions,  which  are  requisite 
for  the  manifestation  of  Muscular  Irritability.  It  has  been  already 
pointed  out,  how  close  is  the  dependence  of  the  property  upon  the  due 
nutrition  of  the  tissue ;  but  the  property  cannot  be  long  exercised  ex- 


216      DEPENDENCE  OF  MUSCULAR  CONTRACTION  UPON  OXYGEN. 

cept  under  another  condition,  which  is  consequently  of  almost  equal 
importance, — the  circulation  of  arterial  blood  through  the  substance 
of  the  muscle.  The  length  of  time  during  which  the  contractility 
remains,  after  the  circulation  has  ceased,  has  been  shown  by  Dr.  M. 
Hall  to  vary  inversely  to  the  activity  of  the  respiration  of  the  animal. 
Thus  in  cold-blooded  animals,  the  standard  of  whose  respiration  is 
low,  the  contractility  remains  for  many  hours  after  death,  even  in  the 
voluntary  muscles ;  and  the  muscles  of  organic  life  retain  it  with 
great  tenacity.  Thus  the  heart  of  a  Frog  will  go  on  pulsating  for 
many  hours  after  its  removal  frop  the  body  ;  and  the  heart  of  a  Stur- 
geon, which  had  been  inflated  with  air  and  hung  up  to  dry,  has  been 
seen  to  continue  beating,  until  the  auricle  had  become  absolutely  so 
dry,  as  to  rustle  during  its  movements.  An  exceedingly  feeble  Gal- 
vanic current  is  sufficient  to  excite  the  muscles  of  these  animals  to 
contraction  ;  so  that  Matteuci,  in  his  experiments  upon  Animal  Elec- 
tricity, has  been  accustomed  to  use  the  prepared  hind-leg  of  a  Frog 
as  the  best  indicator  of  the  passage  of  an  electric  current.  Among 
warm-blooded  animals,  the  same  rule  holds  good,  in  regard  to  the 
inverse  proportion  of  the  duration  of  irritability,  and  the  amount  of 
respiration  ;  for  the  muscles  of  Birds  lose  this  property  at  an  earlier 
period  after  the  cessation  of  the  circulation,  than  do  those  of  Mammals. 
From  experiments  on  the  bodies  of  executed  criminals,  who  were  pre- 
viously in  good  health,  Nysten  ascertained  that,  in  the  human  subject, 
the  contractility  of  the  several  muscular  structures,  as  tested  by  Galva- 
nism, departs  in  the  following  time  and  order : — the  left  ventricle  of  the 
heart  first;  the  intestinal  canal  at  the  end  of  45  or  55  minutes;  the 
urinary  bladder  nearly  at  the  same  time ;  the  right  ventricle  after  the 
lapse  of  an  hour ;  the  oesophagus  at  the  expiration  of  an  hour  and  a 
half;  the  iris  a  quarter  of  an  hour  later;  and  lastly,  the  ventricles  of 
the  heart,  especially  the  right,  which  in  one  instance  contracted  16J 
hours  after  death. 

359.  That  the  circulation  of  arterial  or  oxygenated  blood  through 
the  muscles,  is  the  essential  condition  of  the  continuance  of  their  irrita- 
bility, appears  from  this, — that  after  the  general  death  of  the  system, 
and  even  after  the  removal  of  the  brain  and  spinal  cord,  the  muscles 
will  preserve  their  irritability,  and  the  action  of  the  heart  itself  will 
continue  for  a  long  time,  provided  that  the  circulation  be  kept  up 
through  the  lungs  by  artificial  respiration,  on  the  principles  hereafter 
to  be  explained.  (§  688.)  But  if,  whilst  the  general  circulation 
continues,  the  circulation  through  a  particular  muscular  part  be  inter- 
rupted, that  organ  will  lose  its  contractility  earlier  than  usual.  Thus 
it  has  been  shown  by  Mr.  Erichsen,  that,  if  the  coronary  arteries 
(supplying  the  substance  of  the  heart)  be  tied  in  a  dog  or  a  rabbit, 
after  the  animal  has  been  pithed,  and  the  circulation  is  being  main- 
tained by  artificial  respiration,  the  pulsation  of  the  heart  will  only  go 
on  for  about  23  minutes  after  the  ligature  has  been  applied,  or  about 
33  minutes  after  the  death  of  the  animal ;  instead  of  continuing  for  90 
minutes,  which  it  will  do  under  other  circumstances.    Further,  if  blood 


DISINTEGRATION  OF  MUSCLE  BY  USE.  217 

charged  with  carbonic  acid,  instead  of  with  oxygen,  circulate  through 
the  muscles,  their  irritability  is  speedily  impaired,  and  is  even  de- 
stroyed. This  is  best  seen,  when  animals  are  killed  by  being  caused 
to  breathe  an  atmosphere  highly  charged  with  carbonic  acid  ;  the  irri- 
tability of  their  muscles  departing  as  soon  as  they  are  dead.  In  fact, 
the  destruction  of  the  irritability  of  the  heart,  by  the  circulation  of 
venous  blood  through  its  substance,  is  one  of  the  immediate  causes  of 
death.  A  similar  effect  is  produced  by  the  respiration  of  other  gases, 
which  are  either  poisonous  in  themselves,  or  which  prevent  the  inter- 
change of  carbonic  acid  and  oxygen,  which  ought  to  take  place  in  the 
lungs.  On  the  other  hand,  when  animals  have  been  made  to  respire 
oxygen,  and  their  blood  has  been  consequently  highly  arterialized, 
the  contractility  of  their  muscles  is  retained  for  a  longer  time  than 
usual. 

360.  Hence  we  may  conclude  the  presence  of  oxygen  in  the  blood 
to  be  one  of  the  conditions  of  muscular  contraction;  although  it  is 
much  less  essential  in  the  case  of  cold-blooded,  than  in  that  of  warm- 
blooded animals.  It  is  interesting  to  remark,*  that  the  muscles  of  %- 
bernating  warm-blooded  Mammals  are  reduced  for  a  time  to  the  level 
of  those  of  cold-blooded  animals ;  their  contractility  being  retained 
almost  as  long  as  that  of  the  latter ;  thus  confirming  the  general  prin- 
ciple already  stated  as  to  the  relation  between  the  amount  of  respira- 
tion, and  the  duration  of  the  irritability. 

361.  The  Muscles,  as  we  have  seen,  are  largely  supplied  with 
blood ;  and  the  flow  of  blood  into  them  increases  with  the  use  that  is 
made  of  them.  The  demand  for  nutrition  is  obviously  augmented,  in 
proportion  to  the  activity  of  the  exercise  of  the  Muscular  system ;  for 
the  slightest  observation  suffices  to  show,  that  a  much  smaller  am  ount 
of  nourishment  is  sufficient  to  sustain  the  body  in  its  normal  condition, 
when  the  Muscular  system  is  not  actively  exercised,  than  when  it  is  in 
energetic  operation.  The  quantity  w^hich  is  ample  for  an  individual 
leading  an  inactive  life,  is  far  too  little  for  the  same  person  in  the  full 
exercise  of  his  muscular  powers.  Again,  there  is  evidence  derived 
from  observation  of  the  relative  amount  of  the  solid  matters  excreted 
from  the  body  under  different  circumstances,  that  a  waste  or  disintegra- 
tion of  the  muscular  tissue  takes  place,  whenever  it  is  actively  em- 
ployed ;  and  this  in  a  degree  strictly  proportional  to  the  amount  of  force 
which  it  is  called  upon  to  exercise.  In  fact,  it  would  appear  that  this 
waste  is  a  necessary  consequence  of  the  exercise  of  the  muscle  ;■ — every 
act  of  contraction  involving  the  death  and  decomposition  of  a  certain 
amount  of  tissue.  And  as  the  presence  of  oxygen  is  always  necessary 
for  the  decomposition  of  organic  substances,  so  do  we  find  that  the 
penetration  of  the  muscular  tissue  by  oxygenated  blood  is  essential  to 
the  manifestation  of  its  contractile  power. 

362.  Every  act  of  contraction,  then,  may  be  said  to  involve  the 
death  of  a  certain  amount  of  muscular  tissue;  and  the  products 
of  decomposition  which  consist  of  the  elements  of  muscular  fibre 
united  with  the  oxygen  of  the  arterial  blood,  are  carried  off  by  the 


218  DEPENDENCE  OF  IRRITABILITY  UPON  NUTRITION. 

venous  current.  On  the  other  hand,  the  muscular  substance  is  re- 
paired by  an  act  of  nutrition,  at  the  expense  of  the  fibrin  supplied  to 
it  by  the  circulating  fluid.  There  are  certain  muscles,  as  the  heart, 
and  the  muscles  of  respiration,  whose  action  is  necessarily  constant; 
and  their  reparation  must  take  place  as  unceasingly  as  their  waste.  In 
these  muscles  no  sense  of  fatigue  is  ever  experienced.  But  in  the 
muscles  which  are  usually  put  in  action  by  the  will,  this  is  not  the  case. 
Any  prolonged  exertion  of  them  induces  fatigue ;  and  this  fatigue  is 
an  evidence  of  their  impaired  condition,  and  of  the  necessity  of  rest 
to  impart  to  them  a  renewal  of  vigour.  The  rest  of  muscles  is  essen- 
tial to  the  recovery  of  their  powers  ;  and  this  recovery  is  due  to  the 
nutritive  operations,  which  then  take  place  unchecked,  and  which 
repair  the  losses  previously  sustained.  The  permanently  increased 
flow  of  blood  to  a  muscle,  which  takes  place  when  it  is  continually 
being  called  into  vigorous  action,  is  thus  on  the  one  hand  occasioned 
by  the  demand  for  oxygenated  blood  created  by  its  use,  whilst  on  the 
other  hand  it  tends  to  increase  the  power  of  the  muscle  by  an  aug- 
mentation of  its  nutrition.  Hence  it  is,  that  the  more  a  muscle  is 
exercised,  the  more  vigorous  and  more  bulky  does  it  become.  This 
is  equally  the  case  whether  the  exercise  of  the  muscle  be  voluntary 
or  not.  We  see  examples  of  it  in  the  arms  of  the  smith  and  in  the 
legs  of  the  opera  dancer ;  and  we  have  a  still  more  striking  manifesta- 
tion of  it  in  those  cases,  in  which  an  obstruction  to  the  exit  of  urine 
through  the  urethra,  has  called  for  increased  efforts  on  the  part  of  the 
bladder,  the  continuance  of  which  gives  rise  to  an  extraordinary  aug- 
mentation in  the  thickness  of  its  muscular  coat. 

363.  Thus  we  see  that  the  property  of  Irritability  is  a  vital  endow- 
ment peculiar  to  muscular  tissue,  and  dependent  for  its  existence  upon 
due  nutrition  of  that  tissue ;  that  it  may  be  called  into  exercise  by  cer- 
tain stimuli,  applied  either  to  the  muscle  itself,  or  to  the  nerve  sup- 
plying it,  provided  that  the  muscle  be  also  permeated  with  oxygen  ; 
that  it  may  be  exhausted  by  repeated  stimulation,  but  is  then  recov- 
ered by  rest,  provided  that  there  be  no  obstacle  to  the  nutrition  of 
the  muscle ;  that  the  nutrition  of  the  muscle  is  impaired  by  continued 
repose,  and  that  its  irritability  diminishes  in  the  same  proportion ;  that 
the  nutrition  is  increased  by  frequent  use,  and  that  the  power  of  the 
muscle  then  augments  in  like  degree  ;  and  finally  that  the  departure  of 
muscular  power,  which  ensues  upon  the  general  death  of  the  system, 
is  dependent  in  part  upon  the  cessation  of  the  supply  of  oxygen,  and 
in  part  upon  changes  in  the  composition  of  the  muscle  itself,  which 
are  no  longer  compensated  by  the  functions  that  keep  it  in  its  normal 
condition  during  life. — The  rapidity  of  these  changes  is  the  greatest 
in  warm-blooded  animals,  in  which  also  the  muscular  irritability  is 
most  dependent  upon  the  presence  of  oxygen  in  the  muscular  sub- 
stance ;  consequently  the  irritability  departs  after  death  much  more 
speedily  in  these  than  in  cold-blooded  animals. 

364.  We  have  now  to  consider  the  other  form  of  Contractility, 
which  produces  a  constant  tendency  to  contraction  in  the  Muscular 


TONICITY  OF  MUSCLES.— RIGOR  MORTIS.  219 

fibre,  but  which  is  so  far  different  from  simple  Elasticity,  that  it  abates 
after  death,  before  decomposition  has  taken  place.  This  Tonicity 
manifests  itself  in  the  retraction  which  takes  place  in  the  ends  of  a 
living  muscle,  when  it  is  divided ;  the  retraction  being  permanent, 
and  greater  than  that  of  a  dead  muscle.  It  also  shows  itself  in  the 
permanent  flexure  of  joints,  when,  by  paralysis  of  the  extensors,  the 
tonic  contraction  of  the  flexors  is  not  antagonized.  In  the  healthy 
state,  it  would  seem  as  if  the  tonicity  of  the  several  groups  of  muscles 
was  so  adjusted,  as  to  be  in  mutual  counterpoise  ;  but  the  balance  is 
destroyed  when,  in  consequence  of  paralysis,  or  of  impaired  nutrition 
from  other  causes,  the  tonicity  of  one  set  is  weakened.  This  is  the 
case,  for  example,  in  the  lead-palsy ;  in  which  the  extensors  of  the 
forearm  and  hand  lose  their  power,  so  that  the  tonic  contraction  of 
the  flexors  keeps  the  fingers  constantly  bent  upon  the  palm.  It 
would  seem,  however,  that  the  tonicity  of  the  flexors  is  usually  greater 
than  that  of  the  extensors ;  as  the  former  predominate,  when  all  are 
equally  withdrawn  from  the  control  of  the  nervous  system,  in  profound 
sleep. 

365.  The  Tonicity  is  much  greater,  relatively  to  the  amount  of 
irritability,  in  the  non-striated,  than  in  the  striated  fibre ;  and  it  is 
particularly  remarkable  in  the  fibrous  c^t  of  the  arteries,  in  which  it 
is  diflScult  to  procure  any  decided  indication  of  irritability  by  the  ap- 
plication of  stimuli.  It  is  by  this  tonicity  of  the  walls  of  the  arteries, 
that  they  are  kept  in  a  state  of  constant  moderate  contraction  upon 
their  contents ;  and  that,  when  they  are  emptied,  they  contract  until 
the  tube  is  nearly  obliterated.  If  its  amount  be  too  great  (as  some- 
times happens)  the  artery  approaches  the  condition  of  a  rigid  tube ; 
which,  as  will  be  shown  hereafter,  is  unfavourable  to  the  regularity 
of  the  flow  of  blood  through  it,  though  the  rate  is  increased.  On  the 
other  hand,  if  it  be  unduly  diminished,  the  circulation  is  retarded, 
by  the  tendency  of  the  arterial  walls  to  yield  too  much  to  the  pulse- 
wave. 

366.  This  property  is  very  greatly  affected  by  temperature;  being 
diminished  by  w-armth,  and  increased  by  cold.  Thus  when  an  artery 
is  exposed  to  the  air  for  some  time,  the  lowering  of  its  temperature 
occasions  its  contraction  to  such  an  extent,  that  its  tube  may  be  almost 
obliterated.  And  in  the  operation  of  crimping  fish,  immersion  of  the 
body  in  cold  water,  after  the  muscles  have  been  divided,  increases 
the  tonic  contraction  of  the  muscles,  and  thus  improves  the  firmness 
to  their  substance,  w^hich  it  is  the  object  of  this  operation  to  produce. 

367.  The  Rigor  Mortis,  or  death-stiffening  of  the  muscles,  is  pro- 
bably to  be  regarded  as  a  manifestation  of  this  property,  occurring 
after  all  the  Irritability  of  the  muscles  has  departed,  but  before  any 
putrefactive  change  has  commenced.  This  phenomenon  is  rarely 
absent ;  although  it  may  be  so  slight,  and  may  last  for  so  short  a  time, 
as  to  escape  observation.  The  period  which  elapses  before  its  com- 
mencement is  as  variable  as  its  duration ;  and  both  seem  to  be  de- 
pendent upon  the  vital  condition  of  the  system  at  the  time  of  death. 


220  RIGOR  MORTIS. 

When  it  has  been  weakened  or  depressed  by  previous  disease,  the 
irritability  of  the  muscles  speedily  departs  ;  and  the  stiffening  comes 
on  early,  and  lasts  but  a  short  time.  Thus,  after  death  from  Typhus, 
the  limbs  have  been  sometimes  known  to  stiffen  within  15  or  20 
minutes.  On  the  other  hand,  when  the  general  vigour  of  the  system 
has  not  been  previously  impaired,  and  death  has  resulted  from  some 
sudden  cause,  the  irritability  of  the  muscles  is  of  longer  duration, 
and  their  stiffening  is  consequently  deferred.  The  commencement  of 
the  rigidity  usually  takes  place  within  seven  hours  after  death ;  but 
twenty  or  even  thirty  hours  may  elapse  before  it  shows  itself.  Its 
general  duration  is  from  twenty-four  to  thirty-six  hours  ;  but  it  may 
pass  off  much  more  rapidly,  or  it  may  be  prolonged  through  several 
days.  It  affects  all  the  muscles  composed  of  the  striated  fibre  with 
nearly  the  same  intensity ;  except  that  the  flexors  usually  contract 
more  strongly  than  the  extensors  (as  in  sleep),  the  fingers  being 
closed  upon  the  palm,  the  hand  bending  on  the  forearm,  and  the 
lower  jaw  being  drawn  firmly  against  the  upper.  And  it  even  mani- 
fests itself  in  muscles  that  have  been  thrown  out  of  use  by  paralysis, 
provided  that  their  nutrition  has  not  been  seriously  impaired. 

368.  This  tonic  contraction,  however,  is  most  remarkably  mani- 
fested in  the  non-striated  fibre ;  and  especially  in  the  heart  and  blood- 
vessels. As  soon  as  the  muscular  walls  of  the  several  cavities  lose 
their  irritability,  they  begin  to  contract  forcibly  upon  their  contents, 
and  thus  become  stiff  and  firm,  although  they  were  previously  flaccid. 
In  this  manner,  the  ventricles  of  the  heart,  which  are  the  first  parts 
to  lose  their  irritability,  become  rigid  and  contracted  within  an  hour 
or  two  after  death;  and  usually  remain  in  that  state  for  ten  or  twelve 
hours,  sometimes  for  twenty-four  or  thirty-six,  then  again  becoming 
relaxed  and  flaccid.  This  rigid  contracted  state  of  the  heart,  in  which 
the  walls  are  thickened  and  the  cavities  diminished,  was  formerly 
supposed  to  be  a  result  of  disease,  and  was  termed  concentric  hyper- 
trophy; but  it  is  now  known  to  be  the  natural  condition  of  the  organ, 
at  the  period  when  the  rigor  mortis  occurs  in  it. — The  contraction  of 
the  arterial  tubes  is  so  great,  as  to  produce  for  the  time  a  great  dimi- 
nution in  their  calibre ;  and  this,  doubtless,  contributes  to  the  passage 
of  the  blood  from  the  arterial  into  the  venous  system,  which  almost 
invariably  takes  place  within  a  few  hours  after  death.  The  arteries 
then  enlarge  again,  and  become  quite  flaccid,  their  tubes  being  emptied 
of  the  previous  contents ;  and  it  was  from  this  circumstance,  that  the 
ancient  physiologists  were  led  to  imagine  that  the  arteries  are  not 
destined  to  carry  blood,  but  air. 

369.  As  soon  as  the  Rigor  Mortis  departs,  the  muscles  pass  into 
a  state  of  decomposition  ;  in  fact,  it  is  by  the  commencement  of  de- 
composition, that  the  cessation  of  this  vital  property  is  occasioned. 
Thus  we  may  regard  the  Rigor  Mortis  as  the  last  act  of  the  Muscu- 
lar Contractility ;  and  in  this  respect  it  corresponds  with  the  coagula- 
tion of  the  blood,  which  also  is  the  closing  act  of  its  life,  when  it  is 
drawn  from  the  living  body,  or  has  ceased  to  circulate  (§  184). 


FORCE  DEVELOPED  IN  MUSCULAR  CONTRACTION.  221 

There  are,  indeed,  many  remarkable  points  of  correspondence  be- 
tween the  two  phenomena;  which  have  induced  some  physiologists 
to  believe,  that  rigor  mortis  is  in  fact  nothing  else  than  the  coagula- 
tion of  the  blood  in  the  muscles.  It  has  been  shown  by  Mr.  Bowman, 
however,  that  the  stiffening  of  the  muscles  after  death  is  due  to  the 
permanent  contraction  of  their  component  fibres,  and  that  the  coagu- 
lation of  the  blood  can  have  nothing  to  do  with  it.  Nevertheless, 
this  contraction  may  be  considered  as  being,  for  the  muscular  fibre, 
very  much  the  same  kind  of  phenomenon  as  the  coagulation  of  the 
fluid  fibrin  of  the  blood, — especially  resembling  the  subsequent  con- 
traction of  the  clot,  which  takes  place  gradually,  within  a  few  hours 
after  its  separation.  The  causes  which  prevent  the  coagulation  of 
the  blood  after  death  (§  187),  usually  prevent  also  this  last  manifes- 
tation of  the  tenacity  of  the  muscles ;  their  vitality  being  completely 
destroyed,  like  that  of  the  blood,  by  sudden  and  powerful  shocks 
operating  on  the  nervous  system,  or  by  the  complete  exhaustion  con- 
sequent upon  violent  and  long-continued  exertion,  as  when  animals 
are  run  to  death.  And  again,  the  tonicity  of  muscles  survives  the 
freezing  process ;  manifesting  itself  by  contraction  and  rigidity,  in  a 
muscle  that  has  been  frozen  immediately  after  death,  and  is  subse- 
quently thawed ;  just  as  the  peculiar  properties  of  the  fibrin  of  the 
blood  cause  its  coagulation  upon  being  thawed,  if  it  have  been  frozen 
immediately  upon  being  drawn  from  the  vessels. 

370.  The  power  by  which  the  elements  of  Muscular  fibre  are 
caused  to  approach  one  another  in  the  exercise  of  their  Contractility, 
differs  from  any  other  with  which  we  are  acquainted.  Its  complete 
dependence  upon  the  life  of  the  tissue  is  remarkably  shown  by  the 
fact  (ascertained  by  Valentin),  that,  after  the  cessation  of  the  irritabi- 
lity, the  muscles  tear  with  a  far  less  weight,  than  they  were  previously 
able  to  draw,  when  excited  by  galvanism ;  so  that  their  contractile 
force  is  much  greater  than  that,  which  the  simple  cohesiveness  of  the 
tissue  can  sustain.  Moreover,  it  has  been  shown  by  the  experiments 
of  Schwann,  that  the  contractile  force  is  greatest,  when  the  muscle  is 
most  extended ;  so  that,  with  the  same  stimulus,  it  can  overcome  a 
greater  resistance  by  its  contraction,  when  it  has  been  previously 
stretched  to  its  full  length,  than  it  can  when  it  has  been  already  in 
part  shortened  by  the  exercise  of  its  contractile  force.  The  power 
diminishes  progressively  with  the  further  shortening  of  the  muscle ; 
until  at  last  no  further  contraction  can  be  produced  by  any  stimulus, 
the  extreme  limit  having  been  reached.  Hence  it  seems  as  if  the 
contractile  force  of  Muscles  differs  completely  from  other  forms  of 
Attraction,  as  those  of  Gravitation,  Electricity,  &c.;  since  it  is  the 
universal  law  of  their  operation,  that  the  force  increases,  in  proportion 
to  the  decrease  between  the  squares  of  the  distances  between  the 
attracting  bodies  ;  whilst,  in  the  case  of  muscle  the  force  decreases,  in 
proportion  as  the  distance  between  the  attracting  particles  decreases. 
But  it  is  to  be  remembered  that  the  law  of  attraction  just  quoted  sup- 
poses the  particles  to  be  quite  free  to  approach  one  another ;  and  this 


222      NERVOUS  SYSTEM;— ITS  GENERAL  STRUCTURE. 

they  obviously  are  not  in  the  contraction  of  a  Muscle,  since  the  ap- 
proach cannot  take  place  without  a  change  of  place  between  the  solid 
and  fluid  elements  (§  354).  Hence  it  is  difficult,  if  not  impossible, 
to  discover  the  law,  which  shall  truly  express  the  nature  of  the  at- 
traction between  the  ultimate  particles  of  Muscle  at  different  dis- 
tances ;  but  the  law  discovered  by  Schwann  expresses  the  force 
actually  developed,  at  the  different  states  of  muscular  contraction. 

371.  It  has  been  ascertained  by  the  researches  of  MM.  Becquerel 
and  Breschet,  that  the  temperature  of  a  muscle  rises,  when  it  is  thrown 
into  energetic  contraction.  The  increase  is  ordinarily  but  about  1° 
Fahr.;  but  it  may  amount  to  twice  as  much,  if  the  muscle  be  kept  in 
action  for  some  time,  as  in  the  exercise  of  sawing.  Two  causes  may 
be  assigned  for  this  increase.  It  may  depend  upon  the  chemical 
changes  which  take  place  in  the  Muscles,  as  a  necessary  condition  of 
the  production  of  its  force  (§  361);  or  it  maybe  the  result  of  the  fric- 
tion taking  place  between  different  parts,  during  the  constant  inter- 
change of  their  actions  (§  356).  Perhaps  both  these  causes  concur 
in  producing  the  effect. 

372.  The  JYervous  System,  taken  as  a  whole,  is  the  instrument  of 
all  those  operations,  which  peculiarly  distinguish  the  Animal  from  the 
Plant;  and  it  serves  many  additional  purposes,  connected  with  the 
Organic  or  Vegetative  functions,  which  the  peculiar  arrangements  of 
the  Animal  body  involve.  Wherever  a  distinct  Nervous  System  can 
be  made  out  (which  has  not  yet  been  found  possible  in  the  lowest 
Animals),  it  consists  of  two  very  different  forms  of  structure ;  the 
presence  of  both  of  which,  therefore,  is  essential  to  our  idea  of  it  as 
a  whole.  We  observe,  in  the  first  place,  that  it  is  formed  of  trunks, 
which  are  distributed  to  the  different  parts  of  the  body,  especially  to 
the  muscles  and  to  the  sensory  surfaces  ;  and  of  ganglia,  which  some- 
times appear  merely  as  knots  or  enlargements  on  these  trunks,  but 
which,  in  other  cases,  have  rather  the  character  of  central  masses, 
from  which  the  trunks  proceed.  Now  it  is  easily  established  by  experi- 
ment, that  the  active  powers  of  the  nervous  system  reside  in  the  ganglia; 
and  that  the  trunks  serve  merely  as  conductors  of  the  influence  which 
is  to  be  propagated  towards  or  from  them.  For  if  a  trunk  be  divided 
in  any  part  of  its  course,  all  the  parts  to  which  the  portion  thus  cut 
off  from  the  ganglion  is  distributed,  are  completely  paralyzed  ;  that  is, 
no  impression  made  upon  them  is  felt  as  a  sensation,  and  no  motion 
can  be  excited  in  them  by  any  act  of  the  mind.  Or  if  the  substance 
of  the  ganglion  be  destroyed,  all  the  parts,  which  are  exclusively 
supplied  by  nervous  trunks  proceeding  from  it,  are  in  like  manner 
paralyzed.  But  if,  when  a  trunk  is  divided,  the  portion  still  con- 
nected with  the  ganglion  be  pinched,  or  otherwise  irritated,  sensations 
are  felt,  which  are  referred  to  the  points  supplied  by  the  separated 
portion  of  the  trunk ;  which  shows  that  the  part  remaining  in  con- 
nection with  the  ganglion  is  still  capable  of  conveying  impressions, 
and  that  the  ganglion  itself  receives  these  impressions  and  makes 
them  felt  as  sensations.     On  the  other  hand,  if  the  separated  portion 


STRUCTURE  OF  NERVOUS  FIBRES.  223 

of  the  trunk  be  irritated,  motions  are  excited  in  the  muscles  which  it 
supplies ;  showing  that  it  is  still  capable  of  conveying  the  motor 
influence,  though  cut  off  from  the  usual  source  of  that  influence. 

373.  When  we  minutely  examine  the  trunks  of  the  nerves,  we  find 
that  they  are  composed,  in  the  first  place,  of  a  JYeurilemma  or  nerve- 
sheath,  consisting  of  white  fibrous  tissue ;  the  office  of  which  is  evi- 
dently that  of  protecting  the  nerve-tubes,  and  of  isolating  them  from 
the  surrounding  structures,  at  the  same  time  that  it  allows  blood- 
vessels to  pass  into  the  interior  of  the  trunk.  From  the  interior  of 
the  neurilemma,  thin  layers  of  areolar  tissue  pass  into  the  midst  of 
the  enclosed  bundle  of  nervous  fibres  ;  separating  it  into  numerous 
smaller  fasciculi,  which  are  thus  bound  together,  and  supplied  with 
blood-vessels.  The  capillaries  are  distributed  very  much  on  the  same 
plan  as  those  of  Muscular  tissue  (Fig.  62);  the  network  being  com- 
posed of  straight  vessels,  which  run  along  the  course  of  the  nerve, 
between  the  nerve-tubes,  and  which  are  connected  at  intervals  by 
transverse  vessels. — When  the  neurilemma  has  been  removed,  and 
the  trunk  has  been  separated  into  its  component  fasciculi,  we  may  still 
further  subdivide  the  fasciculi  themselves,  by  careful  dissection,  until 
we  arrive  at  the  ultimate  nervous  fibre,  which  is  the  essential  element 
of  the  structure.  Two  forms  of  this  fibre  exist  in  the  nerves  of  higher 
animals,  bearing  a  considerable  analogy  to  the  two  forms  of  the  Mus- 
cular fibre  ;  one  appearing  to  be  the  special  instrument  of  the  animal 
functions ;  and  the  other,  which  seems  to  be  less  perfectly  formed, 
having  a  connection  (the  nature  of  which  is  not  yet  well  understood) 
with  the  organic.     These  require  a  separate  description. 

374.  The  Nervous  fibre,  in  its  most  complete  form,  is  distinctly 
tubular.  It  is  composed  externally  of  a  very  delicate  transparent  mem- 
brane, which  is  apparently  quite  homogeneous ;  this  is  obviously 
analogous  to  the  myolemma  of  the  Muscular  fibre,  and  serves,  like  it, 
to  isolate  the  contained  substance  most  completely  from  surrounding 
structures.  This  membranous  tube  is  not  penetrated  by  blood-vessels, 
nor  does  it  branch  or  anastomose  with  others ;  and  there  is  reason  to 
believe  it  to  be  continuous  from  the  origin  to  the  termination  of  the 
nervous  trunk.  Within  the  tube  is  a  hollow  cylinder  of  a  material, 
known  as  the  White  substance  of  Schwann,  which  differs  in  composi- 
tion and  refracting  power  from  the  matter  that  occupies  the  centre  of 
the  tube,  and  of  which  the  outer  and  inner  boundaries  are  marked 
out  by  two  distinct  lines.  And  the  centre  or  axis  of  the  tube  is  occu- 
pied by  a  transparent  substance,  which  is  termed  the  axis-cylinder. 
There  is  reason  to  believe  that  this  last  is  the  essential  component  of 
the  nervous  fibre  ;  and  that  the  hollow  cylinder  which  surrounds  it, 
serves,  like  the  external  investment,  chiefly  for  its  complete  isolation. 
The  whole  of  the  matter  contained  in  the  tubular  sheath  is  extremely 
soft ;  yielding  to  very  slight  pressure.  The  tubular  sheath  itself  varies 
in  density  in  different  parts ;  being  stronger  in  the  nervous  trunks, 
than  in  the  substance  of  the  brain  and  spinal  cord.  In  the  former,  it 
is  not  difficult  to  show,  that  the  regular  form  of  the  nerve-tube  is  a 


224  STRUCTURE  OF  NERVOUS  FIBRES  AND  TRUNKS. 

perfect  cylinder ;  though  a  little  disturbance  will  cause  an  alteration 
in  this, — a  small  excess  of  pressure  in  one  part  forcing  the  contents 
of  the  tube  towards  another,  where  they  are  more  free  to  distend  it, 
and  thus  producing  a  swelling.  The  greater  delicacy  of  the  tubular 
sheath  in  the  latter  causes  this  result  to  take  place  with  yet  more 
readiness  ;  so  that  a  very  little  manipulation,  exercised  upon  the  fibres 
of  the  brain  and  spinal  cord,  or  on  those  of  special  sense,  occasions 
them  to  assume  a  varicose  or  beaded  appearance,  which,  when  first 
observed  by  Ehrenberg,  was  thought  to  be  characteristic  of  them. 
When  the  fibres  of  these  parts,  however,  are  examined  without  any 
such  preparation,  they  are  found  to  be  as  cylindrical  as  the  others. — 
The  diameter  of  the  tubuli  is  usually  between  l-2000th  and  l-4000th 
of  an  inch.  Sometimes,  however,  it  is  as  much  as  1-1 500th  ;  and 
occasionally  as  little  as  l-14000th.  They  are  larger  in  the  nerve- 
trunks  than  in  the  brain  ;  and  they  diminish  in  the  latter  as  they  ap- 
proach the  cortical  substance.  The  fibres  of  the  nerves  of  special 
sense  are  smaller  than  the  average,  in  every  part  of  their  course. 

375.  The  organic  nervous  fibres  (termed  gelatinous  by  Henle)  are 
chiefly  found  in  the  Sympathetic  system,  and  may  be  regarded  as  its 
distinctive  element;  but,  as  we  shall  see  hereafter  (Chap.  XII.),  they 
are  mixed  up  with  the  preceding  in  the  ordinary  nervous  trunks. 
These  fibres  cannot  be  shown  to  consist  of  the  same  variety  of  parts 
as  the  preceding  ;  no  tubular  envelop  can  be  distinguished ;  and  the 
white  substance  of  Schwann  seems  wanting.  They  are  flattened,  soft, 
and  homogeneous  in  their  appearance,  bearing  a  considerable  resem- 
blance to  the  unstriped  Muscular  fibres ;  and,  like  them,  they  contain 
numerous  cell-nuclei,  which  are  arranged  with  tolerable  regularity. 
These  nuclei  are  brought  into  view  by  acetic  acid,  which  dissolves 
the  rest  of  the  fibre,  leaving  them  unchanged.  The  organic  fibres  are 
usually  of  smaller  size  than  the  tubular,  their  diameter  averaging 
between  the  l-6000th  and  the  l-4000th  of  an  inch ;  and  they  some- 
times show  a  disposition  to  split  into  very  delicate  fibrillse.  Being  of 
a  yellowish- gray  colour,  they  have  been  sometimes  distinguished  as 
the  gray  fibres. 

376.  Both  classes  of  fibres  appear  to  run  continuously,  from  one 
extremity  of  the  nervous  cord  to  the  other,  without  anything  like 
union  or  anastomosis  ;  each  ultimate  fibre  probably  having  its  distinct 
office,  which  it  cannot  share  with  another.  The  fasciculi,  or  bundles 
of  fibres,  however,  occasionally  intermix  and  exchange  fibres  with 
each  other ;  and  this  interchange  may  take  place  among  either  the 
fasciculi  of  the  same  trunk,  or  among  those  of  different  trunks.  Its 
object  is  evidently  to  diffuse  among  the  different  branches  the  endow- 
ments of  a  particular  set  of  fibres.  Thus  we  shall  hereafter  see  that, 
in  all  the  Spinal  Nerves  of  Vertebrata,  one  set  of  roots  ministers  to 
sensation,  and  another  to  motion ;  the  sensory  fibres  are  principally 
distributed  to  the  skin,  and  the  motor  fibres  to  the  muscles  ;  but  every 
branch  contains  both  sensory  and  motor  fibres,  which  are  brought 
together  by  the  interlacement  of  those  connected  with  both  sets  of 


COMMUNICATIONS  BETWEEN  NERVOUS  TRUNKS.      225 

roots.  In  the  head,  we  have  some  nervous  trunks  which  have  sen- 
sory roots  alone ;  and  others  which  have  motor  roots  only  ;  these  in 
like  manner  acquire  each  other's  functions  in  some  degree  by  an 
interchange  of  filaments, — the  sensory  trunk  receiving  motor  fibres, 
and  the  motor  trunk  receiving  sensory  fibres.  An  interchange  of 
this  kind,  upon  a  very  extensive  scale,  takes  place  between  the 
Cerebro-spinal  system,  whose  ganglionic  centres  are  the  brain  and 
spinal  cord,  and  the  sympathetic  system,  whose  centres  consist  of  a 
number  of  scattered  ganglia.  The  former  sends  a  large  number  of 
tubular  fibres  into  the  latter,  by  the  twigs  of  communication  near  the 
origins  of  the  Spinal  nerves,  as  well  as  by  their  connecting  branches; 
whilst  the  latter  sends  a  smaller  number  oi gray  or  organic  fibres  into 
the  former. 

377.  Sometimes  we  find  the  fasciculi  of  several  distinct  trunks 
united  into  an  extensive  plexus ;  the  sole  object  of  which  appears  to 
be,  to  give  a  more  advantageous  distribution  to  fibres,  which  all 
possess  corresponding  endowments.  Thus  the  brachial  plexus  mixes 
together  the  fibres  arising  by  five  pairs  of  roots,  on  either  side,  from 
the  spinal  cord;  and  sends  oflf  five  principal  trunks  to  supply  the  arm. 
Now  if  each  of  these  trunks  had  arisen  by  itself,  from  a  distinct  seg- 
ment of  the  spinal  cord,  so  that  the  parts  on  which  it  is  distributed 
had  only  a  single  connection  with  the  nervous  centres,  they  would 
have  been  much  more  liable  to  paralysis  than  they  are.  By  means 
of  the  plexus,  every  part  is  supplied  with  fibres  arising  from  each  of 
the  five  segments  of  the  spinal  cord  ;  and  the  functions  of  the  whole 
must,  therefore,  be  suspended,  before  complete  paralysis  of  any  part 
could  occur,  from  a  cause  which  operates  above  the  plexus.  This 
may  be  experimentally  shown  on  the  Frog,  whose  crural  plexus  is 
formed  by  the  interlacement  of  the  component  fasciculi  of  three  trunks 
on  each  side;  for  section  of  the  roots  of  one  of  these  produces  little 
effect  on  the  general  movements  of  the  limb;  and  even  when  two  are 
divided,  there  is  no  paralysis  of  any  of  its  actions,  all  being  weakened 
in  nearly  an  equal  degree.  It  is  possible  that  by  the  plexiform 
arrangement,  a  consentaneousness  of  action  is  in  some  degree  favoured, 
where  several  distinct  motions  are  to  be  combined  in  one  movement; 
something  of  the  same  kind  is  to  be  met  with  in  numerous  instances, 
among  the  lower  animals,  in  which  the  same  purpose  has  to  be 
attained. 

378.  The  second  primary  element  of  the  Nervous  System,  without 
which  the  fibrous  portion  would  seem  to  be  totally  inoperative,  is 
composed  of  nucleated  cells,  containing  a  finely  granular  substance, 
and  lying  somewhat  loosely  in  the  midst  of  a  minute  plexus  of  blood- 
vessels. Their  normal  form  may  be  regarded  as  globular  (hence 
they  have  been  termed  nerve  or  ganglion- globules) ;  but  this  is  liable 
to  alteration  from  the  compression  they  suflTer,  so  that  they  may  be- 
come oval  or  polygonal.  The  most  remarkable  change  of  form, 
however,  which  they  undergo,  is  by  an  extension  into  one  or  more 
long  processes,  giving  them  a  caudate  or   a  stellate  aspect.     These 

15 


VESICULAR  NERVOUS  SUBSTANCE. 


Fig.  64. 


processes,  according  to  Messrs.  Todd  and  Bowman,  are  composed 
of  a  finely-granular  substance,  resembling  that  of  the  interior  of  the 

vesicle,  with  which  they  seem  to  be  dis- 
tinctly continuous.  They  are  very  liable 
to  break  off  near  the  vesicle ;  but  if  traced 
to  a  distance,  they  are  found  to  divide 
and  subdivide,  and  at  last  to  give  off  some 
extremely  fine  transparent  fibres,  which 
seem  to  interlace  with  those  of  other 
stellate  cells,  and  which  may  perhaps 
(though  this  is  at  present  only  a  surmise) 
become  continuous  with  the  axis-cylin- 
ders of  the  nerve-tubes.  The  size  of  the 
vesicles  is  liable  to  great  variation;  the  globular  ones  are  usually 
between  l-300th  and  1- 1250th  of  an  inch  in  diameter. — Besides  the 
finely-granular  substance  just  mentioned,  these  cells  usually  contain 


Capillary   Network   of   Nervous 
Centres. 


Primitive  fibres  and  ganglionic  globules  of  human  brain,  after  Purkinje.  a,  ganglionic  globules 
lying  amongst  varicose  nerve-tubes,  and  blood-vessels,  in  substance  of  optic  thalamus;  a,  globule 
more  enlarged;  &,  small  vascular  trunk,  b,  b,  globules  with  variously-formed  peduncles,  from  dark 
portion  of  crus  cerebri.    350  Diam. 

a  collection  of  pigment-granules,  which  give  them  a  reddish  or  yel- 
lowish-brown colour.  This,  however,  is  frequently  absent,  especially 
among  the  lower  animals. 

379.  The  vesicles  just  described  are  aggregated  together  in  masses 
of  variable  size  ;  and  are  in  some  degree  held  together  by  the  plexus 
of  blood-vessels,  in  the  midst  of  which  they  lie.  They  are  sometimes 
imbedded  in  a  soft  granular  substance,  which  adheres  closely  to  their 
exterior  and  to  their  processes;  this  is  the  case  in  the  outer  part  of 
the  cortical  substance  of  the  human  brain.  In  other  instances,  each 
cell  is  enclosed  in  a  distinct  envelop,  composed  of  smaller  cells, 
closely  adherent  to  each  other  and  to  the  contained  cell ;  such  an 


STRUCTURE  OF  NERVOUS  GANGLIA. 


227 


arrangement  is  common  in  the  smaller  ganglia,  and  in  the  inner  por- 
tion of  the  cortical  substance  of  the  brain. — The  substance,  which  is 
made  up  of  these  peculiar  cells,  of  the  plexus  of  the  blood-vessels 
in  which  they  lie,  and  of  the  granular  matter  that  is  disposed  amongst 
them,  is  altogether  commonly  known  as  the  cineritious  or  gray  sub- 
stance ;  being  distinguished  by  its  colour,  in  Man  and  the  higher  ani- 
mals at  least,  from  the  white  substance  (composed  of  nerve-tubes)  of 
which  the  trunks  of  the  nerves,  as  well  as  a  large  part  of  the  brain 
and  spinal  cord,  are  made  up.  But  this  distinction  is  by  no  means 
constant;  for  the  gray  colour,  which  is  partly  due  to  the  pigment- 
granules  of  the  cells,  and  partly  to  the  redness  of  the  blood  in  the 
vessels,  is  wanting  in  the  Invertebrata  generally,  and  is  not  charac- 
teristically seen  in  the  classes  of  Fishes  and  Reptiles.  Moreover, 
when  the  ganglionic  substance  exists  in  small  amount,  even  in  Man, 
its  colour  is  not  sufficiently  intense  to  serve  to  distinguish  it;  and,  as 
we  have  already  seen,  there  are  nerve  fibres  which  possess  a  grayish 
hue.  The  real  distinction  evidently  lies  in  theybrm  of  the  ultimate 
structure,  which  is  fibrous  in  the  one  case,  and  cellular  or  vesicular 
in  the  other ;  and  these  terras  will  be  henceforth  used  to  characterize 
the  two  kinds  of  Nervous  tissue,  which  have  been  now  described. 

380.  A  ganglion,  then,  essentially  consists  of  a  collection  of  nerve- 
vesicles  or  ganglion-globules,  interspersed  among  the  nerve-fibres; 
and  it  is  in  the  presence  of  the  former,  that  it  differs  from  a  plexus, 
which  it  frequently  resembles  in  the  arrangement  of  the  latter.  When 
a  nerve  enters  a  ganglion,  its  component  fibres  separate  and  pass 
through  the  ganglion  in  different  directions,  so  as  to  be  variously 
distributed   among  the    branches  which    pass   out   of  it.     In   their 


Fig.  66. 


Dorsal  gnnglion  of  Sympathelic  nerve  of  Mouse  ;— a,  b,  cords  of  connection  with  adjacent  sympa- 
thetic ganglia ;  c,  c.  c,  c,  branches  to  the  viscera  and  spinal  nerve;  rf,  ganglionic  globules  or  cells;  e, 
nervous  fibres  crossing  the  ganglion. 

course,  they  come  in  contact  with  the  vesicular  matter,  which  occu- 
pies the  interior  of  the  ganglion :  and  it  appears  from  Mr.  Newport's 


228      CONNECTION  OF  FIBROUS  AND  VESICULAR  STRUCTURES. 

observations,  that  they  then  become  softer,  and  that  their  diameter 
increases. — The  only  exception  to  the  general  fact,  that  the  vesicular 
matter  occupies  the  centre  of  the  ganglia,  occurs  in  the  brain  of 
Vertebrata,  in  which  it  is  chiefly  disposed  on  the  exterior,  forming  the 
cortical  envelop.  The  reason  for  this  variation  is  probably  to  be  found 
in  the  very  large  amount  of  this  substance,  which  the  brain  of  the 
higher  Vertebrata  contains ;  and  in  the  necessity  of  the  free  access 
of  blood-vessels  to  it,  which  is  provided  for  by  a  great  extension 
of  its  surface  beneath  the  investing  vascular  membrane  (pia  mater), 
more  readily  than  it  could  be  in  any  other  mode. 

381.  But  the  vesicular  matter  is  not  found  in  the  central  masses 
only  of  the  Nervous  System ;  for  it  presents  itself  also  at  those  parts 
of  the  surface  or  periphery^  which  are  peculiarly  destined  to  receive 
the  impressions  that  are  to  be  conveyed  to  the  central  organs.  Thus 
on  the  expansion  of  the  optic  nerve  which  forms  the  retina,  there  is 
a  distinct  layer  of  ganglionic  corpuscles  or  nerve-cells,  with  a  minute 
plexus  of  vessels ;  possessing  all  the  essential  characters  of  the  vesi- 
cular substance  of  the  brain.  Something  of  the  same  kind  has  been 
seen  in  connection  with  the  corresponding  expansions  of  the  olfactive 
and  auditory  nerves  ;  and  it  is  probable  that  the  same  elements  exist 
in  the  papillce  of  the  tongue  and  skin,  to  which  the  nerves  of  taste 
and  touch  are  distributed.  In  these  papillae,  the  nervous  fibres  seem 
to  form  loops,  which  are  accompanied  by  similar  loops  of  blood-ves- 
sels (Figs.  67  and  68).     Hence  we  may  state  it  as  a  general  fact, 


Fig.  68. 


Distribution  of  the  tactile  nerves  at  the  surface  of 
the  lip;  as  seen  in  a  thin  perpendicular  section  of 
the  skin. 


Capillary  network  at  margin  of  lips. 


that,  wherever  a  change  is  to  be  originated^  we  find  vesicular  matter 
with  capillary  blood-vessels  ;  whilst  for  the  conduction  of  such  a 
change  to  distant  parts,  \he  fibrous  structure  is  alone  required. 

382.  The  connection  between  the  fibrous  and  vesicular  portions 
of  the  Nervous  system,  has  not  yet  been  clearly  traced.  It  is  quite 
certain  that,  as  already  remarked,  many  of  the  nerve  fibres  which 
enter  a  ganglion,  come  into  contact  with  its  cells,  passing  over  or 
amongst  them,  and  then  issuing  from  it  again.  And  this  seems  to  be 
the  case  also  with  many  of  the  fibres  which  enter  the  vesicular  matter 


1^ 


M 


CHEMICAL  COMPOSITION  OF  NERVOUS  SUBSTANCE.  229 

of  the  Spinal  cord,  and  the  cortical  substance  of  the  brain.  Some 
observations  recently  made  by  Dr.  Lonsdale  on  the  structure  of  the 
nervous  system  of  foetuses,  in  which  the  brain  and  spinal  cord  were 
wanting,  present  a  remarkable  confirmation  of  this  view.  The 
nervous  cords  were  for  the  most  part  developed ;  and  at  their  origins 
(so  called),  or  central  extremities,  they  were  found  to  hang  as  loose 
threads  in  the  cavities  of  the  cranium  and  spine.  On  examining 
these  threads,  it  was  found  that  the  nerve-tubes  of  which  they  con- 
sisted formed  distinct  loops,  each  of  which  was  composed  of  a  fibre 
that  entered  the  cavity  and  then  returned  from  it.  These  loops  were 
imbedded  in  granular  matter,  resembling  that  interposed  between  the 
vesicles  in  the  cortical  substance  of  the  brain,  and  perhaps  to  be 
regarded  as  vesicular  substance  in  an  early  stage  of  its  formation. 
All  that  is  known  of  the  laws  regulating  the  formation  of  irregular 
productions  like  these,  leads  us  to  the  belief,  that  we  may  rightly 
consider  this  arrangement  of  the  nerve-tubes  as  one  which  exists  in 
the  nervous  centres  when  they  are  fully  developed.  On  the  other 
hand,  the  appearances  observed  by  Messrs.  Todd  and  Bowman  appear 
to  indicate,  that  some  of  the  fibres  originate  directly  in  the  subdivisions 
of  the  filamentous  prolongations  of  the  nerve-cells ;  this,  however, 
must  still  be  regarded  as  an  unsettled  question. 

383.  We  have  now  to  speak  briefly  of  the  Chemical  Composition 
of  the  Nervous  matter; — a  consideration  which  will  be  presently 
shown  to  be  of  much  importance.  As  formerly  remarked  (§  7),  the 
vital  activity  of  a  tissue  is  usually  greater,  as  the  proportion  of  its 
solid  to  its  fluid  contents  is  less ;  and  this  rule  holds  good  most  strik- 
ingly in  regard  to  the  Nervous  substance,  the  vital  activity  of  which 
is  far  greater  than  that  of  any  other  tissue,  and  the  solid  matter  of 
which  usually  constitutes  no  more  than  a  fourth,  and  occasionally 
does  not  exceed  an  eighth,  of  its  entire  weight.  The  proportion  of 
water  is  greatest  in  infancy  and  least  in  middle  life ;  and  it  has  been 
observed  to  be  under  the  average  in  idiots.  Of  the  solid  matter  of 
the  brain,  about  a  third  consists  of  fibrin  or  albumen;  which  is  pro- 
bably the  material  of  the  membrane  of  the  tubuli,  as  well  as  of  the 
tissue  that  connects  them. — It  is  chiefly  with  the  Fatty  matter,  which 
constitutes  about  a  third  of  the  solid  substance,  that  the  attention  of 
Chemists  has  been  occupied.  This  is  stated  by  M.  Fremy  (one  of 
the  most  recent  analysts)  to  contain,  besides  the  ordinary  fatty  mat- 
ters, and  Cholesterine  or  biliary  fat,  two  peculiar  fatty  acids,  termed 
the  Cerebric  and  the  Oleo-phosphoric.  Cerebric  acid,  when  purified,  is 
white,  and  presents  itself  in  crystaline  grains.  It  contains  a  small 
proportion  of  Phosphorus;  and  diflfers  from  the  ordinary  fatty  matter 
in  containing  Nitrogen,  as  also  in  containing  twice  their  proportion 
of  oxygen.  Oleo-phosphoric  acid  is  separated  from  the  former  by  its 
solubility  in  ether;  it  is  of  a  viscid  consistence;  but  when  boiled  for 
a  long  time  in  water  or  alcohol,  it  gradually  loses  its  viscidity,  and 
resolves  itself  into  a  pure  oil,  which  is  elaine,  while  phosphoric  acid 
remains  in  the  liquor.     The  proportion  of  phosphorus  in  the  brain  is 


230  WASTE  AND  RENEWAL  OF  NERVOUS  SUBSTANCE. 

considerable ;  being  from  8  to  18  parts  in  1000  of  the  whole  mass,  or 
from  l-20th  to  l-30th  of  the  whole  solid  matter.  It  seems  to  be  un- 
usually deficient  in  the  brain  of  idiots. — The  remaining  third  and 
sometimes  more,  is  composed  of  a  substance  termed  Osmazome 
(w^hich  seems  to  be  a  proteine-compound  in  a  state  of  decomposi- 
tion), together  with  saline  matter. — No  satisfactory  examination  has 
yet  been  made  into  the  comparative  composition  of  the  vesicular  and 
fibrous  substances ;  but  according  to  Lassaigne,  the  former  contains 
much  more  water  than  the  latter,  and  little  colourless  fat,  but  nearly 
4  per  cent,  of  red  fat,  which  does  not  exist  in  the  other. 

384.  Various  circumstances  lead  to  the  belief,  that  the  Nervous 
tissue,  during  the  whole  period  of  active  life,  is  continually  undergoing 
changes  in  its  substance,  by  decay  and  renewal.  We  know  that, 
after  death,  it  is  one  of  the  first  of  all  the  animal  tissues  to  exhibit 
signs  of  decomposition  ;  and  there  is  no  reason  to  suppose,  that  this 
tendency  is  absent  during  life.  Hence  for  the  simple  maintenance  of 
its  normal  character,  a  considerable  amount  of  nutritive  change  must 
be  required.  But  many  circumstances  further  lead  to  the  conclusion, 
that,  like  all  other  tissues  actively  concerned  in  the  vital  operations, 
Nervous  matter  is  subject  to  a  waste  or  disintegration^  which  bears 
an  exact  proportion  to  the  activity  of  its  operations ; — or,  in  other 
words,  that  every  act  of  the  Nervous  system  involves  the  death  and 
decay  of  a  certain  amount  of  Nervous  matter,  the  replacement  of 
which  will  be  requisite  in  order  to  maintain  the  system  in  a  state  fit 
for  action.  We  shall  hereafter  see,  that  there  are  certain  parts  of  the 
Nervous  system,  particularly  those  which  put  in  action  the  respiratory 
muscles,  which  are  in  a  state  of  unceasing,  though  moderate,  activity; 
and  in  these,  the  constant  nutrition  is  sufficient  to  repair  the  effects  of 
the  constant  decay.  But  those  parts,  which  operate  in  a  more  power- 
ful and  energetic  manner,  and  which  therefore  waste  more  rapidly 
when  in  action,  need  a  season  of  rest  for  their  reparation.  Thus  a 
sense  of  fatigue  is  experienced,  when  the  mind  has  been  long  acting 
through  its  instrument — the  brain  ;  indicating  the  necessity  for  rest 
and  reparation.  And  when  sleep^  or  cessation  of  the  cerebral  func- 
tions, comes  on,  the  process  of  nutrition  takes  place  with  unchecked 
energy,  counterbalances  the  results  of  the  previous  waste,  and  pre- 
pares the  organ  for  a  renewal  of  its  activity.  In  the  healthy  state  of 
the  body,  when  the  exertion  of  the  nervous  system  by  day  does  not 
exceed  that,  which  the  repose  of  the  night  may  compensate,  it  is 
maintained  in  a  condition  which  fits  it  for  constant  moderate  exercise; 
but  unusual  demands  upon  its  powers, — whether  by  the  long-con- 
tinued and  severe  exercise  of  the  intellect,  by  excitement  of  the  emo- 
tions, or  by  the  combination  of  both  in  that  state  of  anxiety  which  the 
circumstances  of  man's  condition  too  frequently  induce, — produce  an 
unusual  waste,  which  requires,  for  the  complete  restoration  of  its 
powers,  a  prolonged  repose. 

385.  There   can   be   no  doubt  that  (from   causes  which  are  not 
known)  the  amount  of  sleep  required  by  different  persons,  for  the 


WASTE  AND  RENEWAL  OF  NERVOUS  SUBSTANCE.  231 

maintenance  of  a  healthy  condition  of  the  nervous  system,  varies 
considerably ;  some  being  able  to  dispense  with  it,  to  a  degree  which 
would  be  exceedingly  injurious  to  others  of  no  greater  mental  ac- 
tivity. Where  a  prolonged  exertion  of  the  mind  has  been  made,  and 
the  natural  tendency  to  sleep  has  been  habitually  resisted,  by  a  strong 
effort  of  the  will,  injurious  results  are  sure  to  follow.  The  bodily 
health  breaks  down,  and  too  frequently  the  mind  itself  is  permanently 
enfeebled.  It  is  obvious  that  the  nutrition  of  the  Nervous  system 
becomes  completely  deranged  ;  and  that  the  tissue  is  no  longer 
formed,  in  the  manner  requisite  for  the  discharge  of  its  healthy  func- 
tions. 

386.  As  the  amount  of  Muscular  tissue  that  has  undergone  disin- 
tegration, is  represented  (other  things  being  equal)  by  the  quantity  of 
urea  in  the  urine,  so  do  we  find  that  an  unusual  waste  of  the  nervous 
matter  is  indicated  by  an  increase  in  the  amount  of  phosphatic  depo- 
sits. No  others  of  the  soft  tissues  contain  any  large  proportion  of 
phosphorus ;  and  the  marked  increase  in  these  deposits,  which  has 
been  continually  observed  to  accompany  long-continued  wear  o{  mind, 
whether  by  intellectual  exertion,  or  by  anxiety,  can  scarcely  be  set 
down  to  any  other  cause.  The  most  satisfactory  proof  is  to  be  found 
in  cases,  in  which  there  is  a  periodical  demand  upon  the  mental 
powers ;  as,  for  example,  among  clergymen,  in  the  preparation  for, 
and  discharge  of,  their  Sunday  duties.  This  is  found  to  be  almost 
invariably  followed  by  the  appearance  of  a  large  quantity  of  the  phos- 
phates in  the  urine.  And  in  cases  in  which  constant  and  severe 
intellectual  exertion  has  impaired  the  nutrition  of  the  brain,  and  has 
consequently  weakened  the  mental  power,  it  is  found  that  any  pre- 
mature attempt  to  renew  the  activity  of  its  exercise,  causes  the 
re-appearance  of  the  excessive  phosphatic  discharge,  which  indicates 
an  undue  waste  of  nervous  matter. 

387.  As  the  disintegration  of  the  Nervous  System  is  thus  propor- 
tional to  its  exercise,  so  must  its  reparation  make  a  corresponding 
demand  upon  the  nutritive  processes.  And  accordingly  we  find,  that 
it  is  very  copiously  supplied  with  blood-vessels ;  and  that  the  amount 
of  food  appropriated  to  its  maintenance  in  an  active  condition,  is  very 
considerable.  This  we  know  from  the  fact,  that  persons  of  active 
minds,  but  sedentary  bodily  habits,  commonly  require  nearly  as  much 
food  as  those  in  whom  the  waste  of  the  Muscular  system  is  greater, 
and  that  of  the  Nervous  system  less,  in  virtue  of  their  bodily  activity 
and  the  less  energetic  operation  of  their  minds. 

388.  The  first  development  of  the  nerve-fibres  appears  to  take 
place,  like  that  of  Muscular  fibre,  by  the  coalescence  of  a  number  of 
primary  cells  into  a  continuous  tube ;  the  granular  fatty  matter  within 
being  the  product  of  a  subsequent  secreting-action.  The  nuclei  of 
the  original  cells  may  be  frequently  seen  in  the  nerve-tubes  at  a  later 
period,  lying  between  their  membranous  walls  and  the  substance 
deposited  in  their  interior.  It  is  probable  that  the  nerve-tubes 
undergo  little  change,  from  the  period  of  their  first  production  to 


232  REGENERATION  OF  NERVOUS  SUBSTANCE. 

that  of  their  final  decay;  their  function,  as  will  be  presently  shown, 
being  of  a  much  more  passive  character,  than  that  of  the  vesicular 
substance.  On  the  other  hand,  the  vesicular  matter  appears  to  be  in 
a  state  of  continual  change,  as  is  the  case  with  all  cells  whose  func- 
tions are  active.  The  appearances  observed  by  Henle  in  the  cortical 
substance  of  the  brain  lead  to  the  belief,  that  there  is  as  continual  a 
succession  of  nerve-cells  as  there  is  of  epidermic  cells;  their  de- 
velopment commencing  at  the  surface,  where  they  are  most  copiously 
supplied  with  blood-vessels  from  the  investing  membrane,  and  pro- 
ceeding as  they  are  carried  towards  the  inner  layers,  where  they 
come  into  more  immediate  relation  with  the  fibrous  portion  of  the 
nerve-structure.  This  change  of  place  is  probably  due  to  the  con- 
tinual death  and  decay  of  the  mature  cells,  where  they  are  connected 
with  the  fibres ;  and  the  constant  production  of  new  generations  at 
the  external  surface, — thus  carrying  the  previously-formed  cells  in- 
wards, in  precisely  the  same  manner  that  the  epidermic  cells  are 
progressively  carried  outwards. 

389.  The  regeneration  of  Nervous  tissue  that  has  been  destroyed, 
takes  place  very  readily  in  continuity  with  that  which  is  left  sound. 
This  may  be  more  easily  proved  by  the  return  of  the  sensory  and 
motor  endowments  of  the  part,  whose  nerves  have  been  separated, 
than  by  microscopic  examination  of  the  reunited  trunks  themselves, 
which  is  not  always  satisfactory.  All  our  knowledge  of  the  functions 
of  the  nervous  system  leads  to  the  belief,  that  perfect  continuity  of 
the  nerve-tubes  is  requisite  for  the  conduction  of  an  impression  of 
any  kind, — whether  this  be  destined  to  produce  motion  or  sensation ; 
and  various  facts,  well  known  to  Surgeons,  prove  that  such  restora- 
tion may  be  complete.  In  the  various  operations  which  are  prac- 
tised for  the  restoration  of  lost  parts,  a  portion  of  tissue  removed 
from  one  spot  is  grafted,  as  it  were,  upon  another ;  its  original  at- 
tachments are  more  or  less  completely  severed, — frequently  entirely 
destroyed, — and  new  ones  are  formed.  Now  in  such  a  part,  as  long 
as  its  original  connections  exist,  and  the  new  ones  are  not  completely 
formed,  the  sensation  is  referred  to  the  spot  from  which  it  was  taken; 
thus  when  a  new  nose  is  made,  by  partly  detaching  and  bringing 
down  a  piece  of  skin  from  the  forehead,  the  patient  at  first  feels, 
when  anything  touches  the  tip  of  his  nose,  as  the  contact  were  really 
with  his  forehead.  After  time  has  been  given,  however,  for  the 
establishment  of  new  connections  with  the  parts,  into  whose  neigh- 
bourhood it  has  been  brought,  the  old  connections  of  the  grafted 
portion  are  completely  severed  ;  and  an  interval  then  ensues,  during 
which  it  frequently  loses  all  sensibility ;  but  after  a  time  its  power  of 
feeling  is  restored,  and  the  sensations  received  through  it  are  referred 
to  the  right  spot. — A  more  familiar  case  is  the  regeneration  of  Skin, 
containing  sensory  nerves,  which  takes  place  in  the  well-managed 
healing  of  wounds  involving  loss  of  substance.  Here  there  must 
obviously  be,  not  merely  a  prolongation  of  the  nerve-tubes  from  the 
subjacent  and  surrounding  trunks,  but  also  a  formation  of  new  sen- 


FUNCTIONAL  CONNECTION  OF  BRAIN  AND  NERVES.  233 

sory  papillae. — A  still  more  striking  example  of  the  regeneration  of 
Nervous  tissue,  however,  is  to  be  found  in  those  cases  (of  which 
there  are  now  several  on  record),  in  which  portions  of  the  extremi- 
ties, that  have  been  completely  severed  by  accident,  have  been  made 
to  adhere  to  the  stump,  and  have  in  time  completely  recovered  their 
connection  with  the  Nervous  as  with  the  other  systems, — as  indi- 
cated by  the  restoration  of  their  sensory  and  motor  endowments. — 
Of  the  degree  in  which  the  vesicular  substance  of  the  Nervous  sys- 
tem may  be  regenerated,  we  have  no  certain  knowledge;  but  there 
can  be  little  doubt,  from  the  activity  of  its  usual  nutritive  changes, 
that  a  complete  reproduction  may  be  effected  in  cases  of  loss  of  sub- 
stance, where  it  can  commence  from  a  neighbouring  mass  of  the  same 
tissue. 

390.  We  have  now  to  inquire  into  the  conditions  under  which  the 
peculiar  properties  of  the  Nervous  System  are  manifested  in  an  active 
form;  and  it  will  first  be  desirable  to  explain,  somewhat  more  in 
detail,  the  nature  of  the  different  operations  to  which  it  is  sub- 
servient. These  operations  present  themselves,  in  their  most  com- 
plex form,  in  Man  and  the  higher  animals;  but  they  may  often  be 
most  satisfactorily  studied  in  the  lower.  In  the  first  place,  when  an 
impression  is  made  upon  any  part  of  the  surface  of  the  body  by 
mechanical  contact,  by  heat,  electricity,  or  any  other  similar  agent, 
— or  upon  the  organs  of  special  sense  (the  eye  and  ear,  the  nose  and 
tongue),  by  light  or  sound,  by  odorous  or  sapid  bodies, — these  im- 
pressions, in  the  healthy  and  wakeful  state  of  the  Nervous  system 
are  felt  as  sensations;  that  is,  the  mind  is  rendered  conscious  of 
them.  Now  there  can  be  no  doubt  that  the  mind  is  immediately 
influenced,  not  by  the  impression  in  the  remote  organ,  but  by  a  cer- 
tain change  in  the  condition  of  the  brain,  excited  or  aroused  by  that 
which  has  originated  elsewhere.  For  if  the  communication  with  the 
brain  be  cut  off',  no  impression  on  the  distant  parts  of  the  nervous 
system  is  felt,  notwithstanding  that  the  mind  remains  perfectly  capa- 
ble of  receiving  it.  The  mind,  then,  is  only  rendered  conscious  of 
external  objects  by  the  influence  which  they  exert  upon  the  brain,  or 
upon  a  certain  part  of  it,  which,  being  the  peculiar  seat  of  sensation, 
is  called  the  sensorium.  Hence  we  recognize,  in  the  process  by 
which  the  mind  is  rendered  conscious  of  external  objects,  three  dis- 
tinct stages  ; — first,  the  reception  of  the  impression  at  the  extremities 
of  the  sensory  nerve ;  second,  the  conduction  of  the  impression, 
along  the  trunk  of  the  nerve,  to  the  sensorium ;  third,  the  change 
excited  by  it  in  the  sensorium  itself,  through  which  sensation  is 
produced.  Here,  then,  the  change  in  the  condition  of  the  nervous 
system  commences  at  the  circumference,  and  is  transmitted  to  the 
centre ;  and  the  fibres  which  are  concerned  in  this  transmission  are 
termed  sensory. 

391.  On  the  other  hand,  when  an  emotion,  an  instinctive  impulse, 
or  an  act  of  the  will,  operates  through  the  brain  to  produce  a  muscular 
contraction,  the  first  change  is  in  the  condition  of  the  brain  itself  or  of 


234  ACTION  OF  NERVES  INDEPENDENTLY  OF  THE  BRAIN. 

a  certain  part  of  it.  The  influence  of  this  change  is  transmitted  by 
the  motor  nerves  to  the  muscles,  among  which  they  are  distributed  ; 
and  the  desired  movement  is  the  result.  Here,  too,  we  have  three 
stages  ;  first,  the  origination  of  the  change  by  the  act  of  the  mind  upon 
the  brain  ;  second,  the  conduction  of  that  change  along  the  motor 
nerves  ;  and  third,  the  stimulation  of  the  muscles  to  contraction.  But 
the  operation  here  commences  at  the  centre ;  and  the  effects  of  the 
change  in  the  brain  are  transmitted  to  the  circumference,  by  a  set  of 
nervous  fibres  which  are  termed  motor.  The  complete  distinctness 
of  these  two  classes  of  fibres  was  first  established  by  Sir  C.  Bell.  It 
is  best  seen  in  the  nerves  of  the  head,  of  which  some  are  purely  sen- 
sory, and  others  purely  motor  ;  but  it  may  also  be  clearly  proved  to 
exist  at  the  roots  of  the  spinal  nerves  (although  their  trunks  possess 
mixed  endowments),  the  posterior  being  sensory,  whilst  the  anterior 
are  motor. 

392.  But  although  sensations  can  only  be  felt  through  the  brain, 
and  voluntary  motions  can  only  be  produced  by  an  action  of  the  mind 
through  the  same  organ,  yet  there  are  many  changes  in  the  animal 
body,  in  which  the  nervous  system  is  concerned,  which  yet  do  not 
involve  the  operation  of  the  brain,  being  produced  without  our  con- 
sciousness being  necessarily  excited,  and  without  any  act  of  the  will, 
or  even  in  opposition  to  its  efforts.  Of  these  actions,  the  spinal  cord 
of  Vertebrata,  and  its  prolongation  within  the  cranium,  are  the  chief 
instruments ;  in  the  Invertebrate  animals,  they  are  performed  by 
various  ganglia,  which  are  usually  disposed  in  the  neighbourhood  .of 
the  organs  to  which  they  minister.  If  the  spinal  cord  of  a  Frog  be 
divided  in  its  back,  above  the  crural  plexus,  so  as  entirely  to  cut  off 
the  nerves  of  the  lower  extremities  from  connection  with  the  brain, 
the  animal  loses  all  voluntary  control  over  these  limbs,  and  no  sign  of 
pain  is  produced  by  any  injury  done  to  them.  But  they  are  not 
thereby  rendered  motionless  ;  for  various  stimuli  applied  to  the  limbs 
themselves  will  cause  movements  in  them.  Thus  if  the  skin  of  the 
foot  be  pinched,  or  if  a  flame  be  applied  to  it,  the  leg  will  be  violently 
retracted.  Or,  if  the  cloaca  be  irritated  by  a  probe,  the  feet  will 
endeavour  to  push  away  the  instrument.  We  have  no  reason  hence 
to  believe,  that  the  animal  feels  the  irritation,  or  intends  to  execute 
these  movements,  in  order  to  escape  from  it ;  for  motions  of  a  similar 
kind  are  exhibited  by  men,  who  have  suffered  injury  of  the  lower 
part  of  the  spinal  cord,  and  who  are  utterly  unconscious,  either  of  the 
irritation,  or  of  the  action  their  limbs  perform. 

393.  We  are  not  to  suppose,  however,  that  the  stimulus  acts  at 
once  upon  the  muscles,  without  the  nervous  system  being  concerned 
at  all ;  throwing  them  into  contraction  by  its  direct  influence.  For  it 
is  quite  certain  that,  unless  the  nervous  trunks  remain  continuous 
with  the  spinal  cord,  and  unless  the  part  of  the  spinal  cord  with  which 
they  are  connected  remains  sound  (although  cut  off  from  connection 
with  the  parts  above,  and  with  the  brain),  no  action  will  be  the  result. 
If  the  trunks  be  divided,  or  eitlwr  of  the  roots  by  which  they  are  con- 


REFLEX  ACTION.— DISTINCT  NERVOUS  FIBRES.  235 

nected  with  the  spinal  cord  be  severed,  or  the  lower  portion  of  the 
spinal  cord  itself  be  injured,  no  stimulation  will  cause  the  muscular 
movements  just  described.  A  very  good  example  of  the  necessity  of 
the  completeness  of  the  nervous  trunks,  which  convey  impressions  to 
and  from  the  central  organ,  is  found  in  the  movements  of  the  iris,  for 
the  contraction  and  dilatation  of  the  pupil.  Here,  the  stimulus  of 
light  upon  the  retina  gives  rise  to  a  change  in  the  condition  of  the 
optic  nerve  ;  which,  being  transmitted  to  a  certain  portion  of  the 
encephalon  with  which  that  nerve  is  connected,  excites  there  a  motor 
impulse  ;  and  this  impulse  is  conveyed  through  a  distinct  nerve  (a 
branch  of  the  third  pair)  to  the  iris,  occasioning  contraction  of  the 
pupil.  Every  one  knows  that  this  adjustment  of  the  size  of  the  pupil 
to  the  amount  of  light,  is  effected  without  any  exertion  of  the  will  on 
his  own  part,  and  even  without  any  consciousness  that  it  is  taking 
place.  It  is  performed,  too,  during  profound  sleep  ;  when  the  influ- 
ence of  light  upon  the  retina  excites  no  consciousness  of  its  presence, 
— when  no  sensation,  therefore,  is  produced  by  it. 

394.  The  class  of  actions  thus  performed,  is  termed  reflex;  and  we 
see  that  every  such  action  involves  the  following  series  of  changes. 
In  the  first  place,  an  impression  is  made  upon  the  extremity  of  a 
nerve,  by  some  external  agent;  just  as  when  sensation  is  to  be  pro- 
duced. Secondly,  this  impression  is  transmitted  by  a  nervous  trunk 
to  the  spinal  cord  in  Vertebrata,  or  to  some  ganglionic  mass  which 
answers  to  it  in  the  Invertebrata.  But  instead  of  being  communi- 
cated by  its  means  to  the  mind,  and  becoming  a  sensation,  it  imme- 
diately and  necessarily  executes  a  motor  impulse  ;  which  is  reflected 
back  as  it  were  to  certain  muscles,  and  by  their  contraction,  gives  rise 
to  a  movement.  We  shall  hereafter  see,  that  nearly  all  those  move- 
ments in  the  animal  body,  which  are  immediately  connected  with  the 
maintenance  of  the  organic  functions,  such  as  those  of  respiration, 
deglutition  (or  swallowing),  the  expulsion  of  the  feces,  urine  and 
fogtus,  &c. — are  performed  in  this  manner. 

395.  Now  there  is  no  reason  to  believe,  that  the  mode  in  which 
impressions  are  conducted  by  the  nervous  trunks,  whether  towards 
or  from  the  nervous  centres,  is  in  any  way  different  from  that  which 
takes  place,  when  sensations  are  to  be  produced,  or  voluntary  motions 
executed.  The  endowments  of  the  trunks  appear  to  be  the  same  in 
both  instances  ;  but  those  of  the  centres  are  different.  We  shall  here- 
after see,  that  the  very  same  trunks  contain  fibres,  originating  at  the 
same  part  of  the  surface,  of  which  some  go  to  the  brain,  and  others  to 
the  spinal  cord ;  impressions  on  the  former,  therefore,  will  produce 
sensations,  whilst  similar  impressions  on  the  latter  will  give  rise  to  no 
sensations,  but  will  excite  a  motor  influence  in  immerfia^e  respondence 
to  their  call.  Again,  the  motor  fibres  which  pass  forth  from  the  spinal 
cord,  and  which  convey  the  reflex  influence  created  by  its  vesicular 
substance,  are  bound  up  in  the  same  trunk  with  others,  which  proceed 
from  the  brain,  and  which  convey  the  influence  of  the  will,  communi- 
cated through  its  gray  or  vesicular  matter.     Thus  we  have  at  least 


236 


NATURE  OF  THE  NERVOUS  POWER. 


two  sets  of  fibres  conveying  impressions  inwards  or  centripetally ;  one 
of  them  being;  sensory  (as  already  explained  §  390)  in  virtue  of  its 
connection  with  the  brain  ;  whilst  the  other  is  excitor^  or  destined  to 
excite  reflex  movements,  through  the  spinal  cord.  These,  taken 
collectively,  may  be  termed  afferent  or  centripetal  fibres.  On  the 
other  hand,  there  are  at  least  two  sets  of  fibres  conveying  motor  im- 
pulses to  the  muscles;  one  of  them  communicating  the  influence  of 
the  mind,  operating  through  the  brain  ;  whilst  the  other  merely  trans- 
mits the  reflex  power  of  the  spinal  cord.  These  in  conjunction  may 
be  called  efferent  or  centrifugal  fibres.  The  following  diagram  may 
assist  the  Student  in  comprehending  the  relations  of  the  elementary 
pans  of  the  Nervous  System. 

396.  Of  the  mode  by  which  the  eflfects  of  changes  in  one  part  of 
the  Nervous  System,  are  thus  instantaneously  transmitted  to  another, 
nothing  whatever  is  known.  There  is  evidently  a  strong  analogy 
between  this  phenomenon,  and  the  instantaneous  transmission  of  the 


Diagram  of  the  origins  and  terminations  of  the  dif- 
ferent groups  of  nervous  fibres ;— a,  o,  vesicular  sub- 
stance of  the  spinal  cord;  6,  6,  6,  vesicular  substance 
of  the  brain;  e,  vesicular  substance  at  the  commence- 
ment of  afferent  nerve,  which  consists  of,  cl,  the  ce- 
rebral division,  or  sensory  nerve,  passing  on  to  the 
brain,  and  si,  the  spinal  division,  or  excilor  nerve, 
which  terminates  in  the  vesicular  substance  of  the 
spinal  cord;  on  the  other  side  we  have  the  efferent  or 
motor  nerve  proceeding  to  the  muscle  d,  likewise  con- 
sistingof  two  divisions, — c2,  the  cerebral  portion,  pro- 
ceeding from  the  brain,  and  conveying  the  influence 
of  the  will  or  of  instinct;  and  52,  the  spinal  division, 
conveying  the  reflex  power  of  the  spinal  cord. 


Electric  power  along  good  conductors ;  and  there  is  this  further 
analogy  between  the  Nervous  and  Electric  agencies,  that  the  latter 
will  produce  many  of  the  eflfects  of  the  former.  Thus  a  very  feeble 
galvanic  current  transmitted  along  a  motor  nerve,  serves  to  excite 
contractions  in  the  muscles  supplied  by  it ;  and  in  like  manner,  a 
galvanic  current  transmitted  along  any  of  the  sensory  nerves,  gives 
rise  to  a  sensation  of  the  kind  to  which  the  nerve  ministers.  Moreover, 
we  shall  hereafter  see,  that  certain  animals  are  capable  of  generating 
Electric  power  in  a  very  remarkable  manner  (Chap.  X.);  and  that  the 
nervous  system  is  in  some  way  essentially  concerned  in  this  opera- 
tion. But  on  the  other  hand,  it  is  quite  certain  that  the  influence 
transmitted  along  the  nerves  of  the  living  body  is  not  ordinary 
electricity;  for  all  attempts  to  procure  manifestations  of  electric 
changes  in  the  state  of  nerves,  that  are  acting  most  energetically  on 
muscles,  have  completely  failed  ;  and  a  nerve  remains  capable  of 
conveying  the  influence  of  electricity,  when  it  has  been  rendered 
unable  to  transmit  the  influence  of  the  brain, — as  by  tying  a  ligature 


CONDITIONS  OF  NERVOUS  ACTION.  237 

round  it,  or  by  tightly  compressing  it  between  the  forceps,  which 
gives  no  interruption  to  the  one  agency,  whilst  it  completely  checks 
the  other. — Notwithstanding,  then,  the  strong  analogy  which  exists 
between  these  two  powers,  we  are  not  warranted  in  regarding  them 
as  identical;  although  it  is  very  possible  that  the  Nervous  power  may 
be  in  time  showm  (as  Magnetism  has  been  proved)  to  be  a  peculiar 
modification  of  ordinary  Electricity,  acting  under  circumstances  in 
many  respects  dissimilar,  and  therefore  appearing  to  possess  distinct 
properties. 

397.  It  is  more  desirable,  however,  that  we  should  understand  the 
conditions  under  which  the  phenomena  of  the  Nervous  system  take 
place,  than  that  we  should  spend  much  time  in  discussing  the  identity  of 
its  peculiar  powers  with  any  others  in  Nature.  The  conducting  Yiowei 
of  the  nervous  fibres  appears  to  remain  with  little  decrease  for  some 
time  after  death,  especially  in  cold-blooded  animals  ;  for  we  can,  by 
pinching,  pricking,  or  otherwise  stimulating  the  motor  trunks,  give 
rise  to  contractions  in  the  muscles  supplied  by  them,  exactly  as  during 
life.  This  power  is  much  lessened  by  the  influence  of  narcotics;  so 
that  if  a  nervous  trunk  be  soaked  in  a  solution  of  opium,  belladonna, 
or  other  powerful  narcotic,  it  ceases  to  be  able  to  convey  the  eflfects 
of  stimuli  to  the  muscles,  some  time  before  the  muscles  themselves 
lose  their  contractile  power.  On  the  other  hand,  it  seems  to  be 
exalted  by  various  irritating  influences ;  so  that,  when  the  nervous 
trunk  has  been  treated  with  strychnia,  or  when  it  has  been  subjected 
to  undue  excitement  in  other  ways,  a  very  slight  change  is  magnified 
(as  it  were)  during  its  transmission,  and  produces  effects  of  unusual 
intensity. 

398.  Now  although  the  conducting  power  of  the  fibrous  structure 
will  continue  for  a  time,  after  the  circulation  through  it  has  ceased, 
the  peculiar  endowments  of  the  vesicular  substance,  by  which  it  ori- 
ginates the  changes  which  the  former  transmits,  are  only  manifested, 
when  blood  is  moving  through  its  capillaries.  Thus  if  the  circula- 
tion through  the  brain  cease  but  for  a  moment,  total  insensibility,  and 
loss  of  the  power  of  voluntary  motion,  immediately  supervene.  The 
brain  is  supplied  with  blood  through  four  arteries, — the  two  internal 
carotids,  and  the  two  vertebrals  ;  and  by  the  communication  of  these 
with  each  other  through  the  circle  of  Willis,  the  circulation  will  still 
be  kept  up,  if  only  one  of  them  should  convey  blood  into  the  cavity 
of  the  cranium.  Hence  it  is  necessary  that  the  flow  of  blood  should 
be  checked  through  all  of  them,  in  order  that  the  functions  of  the 
brain  should  be  suspended ;  and  the  suspension  is  then  complete  and 
instantaneous.  The  best  method  of  effecting  this  was  devised  by  Sir 
Astley  Cooper.  He  tied  both  the  carotid  arteries  in  a  dog;  which, 
for  the  reason  just  mentioned,  did  not  produce  any  decided  influence 
on  the  functions  of  the  brain,  the  circulation  being  kept  up  through 
the  vertebrals.  But  upon  compressing  the  latter,  so  as  to  suspend  the 
flow  of  blood  through  them,  immediate  insensibility,  and  loss  of  vo- 
luntary power,  were  the  result.     When  the  compression  was  taken 


238   DEPENDENCE  OF  NERVOUS  POWER  ON  SUPPLY  OF  BLOOD. 

off,  the  animal  immediately  returned  to  its  usual  state  ;  and  again 
became  suddenly  insensible,  when  the  pressure  was  renewed.  Al- 
though the  functions  of  the  brain  were  thus  suspended,  those  of  the 
spinal  cord  were  not ;  as  was  shown  by  the  occurrence  of  convulsive 
movements.  But  in  the  state  called  Syncope^  or  fainting,  the  suspen- 
sion of  the  circulation,  by  a  failure  in  the  heart's  action,  causes  an 
entire  loss  of  power  in  both  these  centres ;  and  a  complete  cessation 
of  muscular  movement  is  the  result.  This  condition  may  come  on 
instantaneously,  under  the  influence  of  powerful  mental  emotion,  or 
of  some  other  cause,  which  act  primarily  in  suspending  the  heart's 
action,  and  consequently  in  checking  the  circulation;  the  insensi- 
bility, and  loss  of  muscular  power,  are  secondary  results,  depending 
upon  the  suspension  of  the  powers  of  the  nervous  centres,  consequent 
upon  the  cessation  of  the  flow  of  blood  through  them. 

399.  The  due  activity  of  the  vesicular  nervous  matter  is  not  only 
dependent  upon  a  sufficient  supply  of  blood,  but  it  requires  that  this 
blood  should  be  in  a  state  of  extreme  purity ;  for  there  is  no  tissue  in 
the  body,  whose  functions  are  so  readily  deranged,  by  any  departure 
from  the  regular  standard  in  the  circulating  fluid, — whether  this  con- 
sist in  the  alteration  of  the  proportions  of  its  normal  ingredients,  or 
in  the  introduction  of  other  substances  which  have  no  proper  place 
in  it.  One  of  the  most  fertile  sources  of  disturbance  in  the  action  of 
the  brain,  consists  in  the  retention  of  substances  within  the  blood, 
which  ought  to  be  excreted  from  it.  We  shall  hereafter  see,  that 
three  of  the  largest  and  most  important  organs  in  the  body, — the 
lungs,  the  liver,  and  the  kidneys, — have  it  for  their  special  office,  to 
separate  from  the  circulating  fluid  the  products  of  the  decomposition, 
which  is  continually  taking  place  in  the  body  ;  and  thereby  to  main- 
tain its  purity,  and  its  fitness  for  its  important  functions.  Now  if 
these,  from  any  cause,  even  partially  fail  in  their  office,  speedy  dis- 
turbance of  the  functions  of  the  nervous  centres  is  the  result.  Thus 
if  the  lungs  do  not  purify  the  venous  blood  of  its  impregnation  of 
carbonic  acid,  or  restore  to  it  the  proper  proportion  of  oxygen,  the 
functions  of  the  brain  are  seriously  affected.  The  sensations  become 
indistinct,  the  will  loses  its  control  over  the  muscles,  giddiness  and 
faintness  come  on,  and  at  last  complete  insensibility  supervenes. 
Corresponding  symptoms  occur,  though  to  a  less  serious  degree, 
when  the  excretion  of  carbonic  acid  is  but  slightly  impeded.  Thus 
when  a  number  of  persons  are  shut  up  in  an  ill-ventilated  apartment, 
for  a  sufficient  length  of  time  to  raise  the  proportion  of  carbonic  acid 
in  the  air  to  1  or  2  per  cent,  the  continued  purification  of  their  blood 
by  respiration  is  but  insufficiently  performed,  for  reasons  which  will 
be  stated  hereafter  (Chap.  VIII.);  and  the  carbonic  acid  accumulates 
in  their  blood  in  a  sufficient  degree,  to  produce  headache  and  obtuse- 
ness  of  the  mental  powers. — Similar  results  take  place,  as  will  be 
shown  hereafter,  from  the  retention  of  the  substances,  which  ought  to 
be  drawn  off  by  the  liver  and  kidneys;  these,  when  they  accumulate 
in  even  a  trifling  degree,  produce  torpor  of  the  functions  of  the  brain; 


EFFECTS  OF  STIMULANTS  UPON  NERVOUS  POWER.  239 

and,  when  their  proportion  increases,  complete  cessation  of  its  pow- 
ers is  the  result,  their  action  being  precisely  that  of  narcotic  poisons. 
Various  substances  introduced  into  the  blood  may  exert  similar  influ- 
ences ;  depressing  the  activity  of  the  vesicular  substance  of  the  nerv- 
ous centres,  and  consequently  producing  torpidity,  not  merely  in 
regard  to  the  reception  of  impressions,  and  the  performance  of  volun- 
tary motions,  but  also  in  the  mental  operations  generally. 

400.  On  the  other  hand,  various  conditions  of  the  blood,  espe- 
cially those  depending  on  the  presence  of  certain  external  agents, 
produce  an  undue  energy  in  the  functions  of  the  nervous  centres; 
which  energy,  however,  is  almost  invariably  accompanied  by  irregu- 
larity, or  want  of  balance  among  the  different  actions.  Of  this  we 
have  a  familiar  example  in  the  operation  of  alcohol.  Its  first  effect, 
when  taken  in  moderate  quantity,  is  usually  to  produce  a  simple 
increase  in  the  activity  of  the  cerebral  functions.  A  further  dose, 
however,  occasions  not  merely  an  increase,  but  an  irregularity;  de- 
stroying that  powder  of  self-control,  w^hich  is  so  important  a  means  of 
balancing  the  different  tendencies  in  the  healthy  condition  of  the 
mind.  And  a  still  larger  dose  has  the  effect  of  a  narcotic  poison; 
producing  diminution  or  suspension  of  activity  in  all  the  functions  of 
the  brain.  In  sonae  persons,  this  is  the  mode  in  which  the  alcohol 
acts  from  the  first,-^its  stimulating  effects  being  altogether  wanting. 
— A  similar  activity  is  usually  produced  by  the  respiration  of  the 
nitreous  oxide;  which  seems  to  increase  all  the  powers  of  the  mind, 
save  that  of  self-control,  which  it  diminishes;  the  individual,  while 
under  its  influence,  being  the  slave  of  his  impulses,  which  act  on 
his  muscular  system  with  astonishing  energy.  Very  analogous  to 
this,  is  the  incipient  stage  of  mania,  which  is  simply  an  undue 
energy  of  the  cerebral  functions,  at  first  in  some  degree  under  the 
control  of  the  will,  but  afterwards  increasing  to  an  extent  that  ren- 
ders the  individual  completely  powerless  over  himself;  and  showing 
itself  in  the  intensity  of  the  sensations  produced  by  external  objects, 
in  the  vividness  of  the  trains  of  thought,  (which,  being  entirely 
uncontrolled,  succeed  each  other  with  apparent  irregularity,  though 
probably  according  to  the  laws  of  association  and  suggestion,)  and  in 
the  violence  of  the  muscular  actions.  Such  a  state  may  continue  for 
some  time,  without  the  intervention  of  sleep;  but  the  subsequent 
exhaustion  of  nervous  power  is  proportioned  to  the  duration  of  the 
excitement ;  and  frequent  attacks  of  mania  almost  invariably  subside 
at  last  into  imbecility. 

401.  In  these  cases  of  undue  excitement,  there  is  obviously  an 
increase  in  the  supply  of  blood  to  the  head,  as  indicated  by  the  suf- 
fusion of  the  face,  the  injection  of  the  conjunctiva,  the  throbbing  at 
the  temples,  the  pulsation  of  the  carotids ;  and  we  find  that  measures 
which  diminish  the  activity  of  the  circulation  through  the  brain  are 
those  most  effectual  in  subduing  the  excitement.  But  it  does  not  at 
all  follow,  that  this  undue  action  of  the  brain  should  be  connected 
with  an  excess  in  the  whole  amount  of  nutritive  material,  and  should 


240       DEPENDENCE  OF  NERVOUS  POWER  ON  SUPPLY  OF  BLOOD. 

require  general  depletion  for  its  treatment.  In  fact,  a  very  similar 
class  of  symptoms  may  present  itself  under  two  conditions  of  an 
entirely  opposite  kind, — inflammation^  accompanied  with  an  increase 
in  the  proportion  of  fibrin  in  the  blood,  and  requiring  treatment  of 
a  lowering  kind, — and  irritation^  depending  on  a  state  of  blood  in 
which  there  is  a  deficiency  of  solid  materials,  and  requiring  a 
strengthening  and  even  a  stimulating  regimen.  The  skill  of  the 
practitioner  is  often  put  to  the  test,  in  the  due  discrimination  between 
these  states. 

402.  The  preceding  examples  mark  the  influence  of  various  causes 
upon  the  actions  of  the  vesicular  matter  of  the  hrain;  others  might  be 
adduced  to  show  that  the  vesicular  substance  of  the  spinal  cord  is 
also  liable  to  have  its  powers  depressed  or  excited ;  but  these  will 
be  best  adverted  to  hereafter,  when  the  distinct  functions  of  that 
organ  are  under  consideration  (Chap.  XII.).  We  may  simply  notice, 
that  the  stimulating  effect  of  Strychnia  is  peculiarly  and  most  re- 
markably exerted  upon  the  vesicular  substance  of  the  spinal  cord ; 
and  that  a  corresponding  state,  in  which  violent  convulsive  actions 
are  excited  by  the  most  trifling  causes,  sometimes  presents  itself  as  a 
peculiar  form  of  disease,  named  Tetanus,  which  may  be  either  idio- 
pathic^ depending  probably  upon  a  disordered  condition  of  the  blood, 
or  traumatic^  consequent  upon  the  irritation  of  a  wound. 

403.  But,  as  formerly  remarked,  it  is  not  in  the  Nervous  centres 
only  that  changes  originate.  Whenever  an  impression  is  made  upon 
the  surface  of  the  body,  or  upon  the  organs  of  special  sense,  which, 
being  conducted  to  the  nervous  centres,  either  excites  a  sensation  in 
the  brain  (§  390),  or  a  reflex  action  through  the  spinal  cord  (§  392), 
the  reception  and  propagation  of  such  impression  at  the  extremities  of 
the  sensory  nerve  requires  a  set  of  conditions  of  the  same  kind  with 
those  which  we  have  seen  to  exist  in  the  nervous  centres.  In  fact, 
if  we  regard  the  course  of  the  motor  nerves  as  commencing  in  the 
nervous  centres  and  terminating  in  the  muscles,  we  may  with  equal 
justice  consider  that  of  the  sensory  nerves  as  originating  in  their 
peripheral  extremities,  and  terminating  in  the  sensorium.  And,  as 
already  stated  (§  381),  precisely  the  same  kind  of  vesicular  structure 
exists  in  some  (probably  in  all)  of  the  peripheral  expansions  of  the 
sensory  nerves  as  makes  up  the  gray  substance  of  the  brain  and 
spinal  cord.  Now  it  is  easily  shown,  that  the  circulation  of  blood 
through  these  parts  is  just  as  necessary  for  the  original  reception  of 
the  impressions,  as  is  the  circulation  through  the  brain  to  their  re- 
ception as  sensations,  and  to  the  origination  of  motor  impulses  by  an 
act  of  the  will.  W^e  find  that  anything  which  retards  the  circula- 
tion through  a  part  supplied  by  sensory  nerves,  diminishes  its  sensi- 
bility; and  that  if  the  flow  of  blood  be  completely  stagnated,  entire 
insensibility  is  the  result.  A  familiar  example  of  this  is  seen  in  the 
effects  of  prolonged  cold,  which,  by  diminishing,  and  then  entirely 
checking,  the  flow  of  blood  through  the  skin,  produces  first  numb- 
ness, and  then  complete  insensibility  of  the  part.     This  result,  how- 


DEPENDENCE  OF  NERVOUS  POWER  ON  SUPPLY  OF  BLOOD.      241 

ever,  may  be  partly  due  to  the  direct  influence  of  the  cold  upon  the 
nerve-vesicles  themselves,  depressing  their  peculiar  vital  powers  (§ 
97).  The  same  effect  is  produced,  however,  when  the  supply  of 
blood  is  checked  in  any  other  way ;  as,  for  example,  by  pressure  on 
the  artery,  or  by  obstruction  in  its  interior.  Thus,  when  the  main 
artery  of  a  limb  is  tied,  numbness  of  the  extremities  is  immediately 
perceived ;  and  this  continues  until  the  circulation  is  re-established 
by  the  collateral  branches,  when  the  usual  amount  of  sensibility  is 
restored.  Again,  in  the  gangrene  which  depends  upon  obstruction 
of  the  arterial  trunks  by  a  fibrinous  clot  in  their  interior,  diminution 
of  sensibility,  consequent  upon  the  insufficient  circulation,  is  one  of 
the  first  symptoms. 

404.  On  the  other  hand,  increased  circulation  of  blood  through  a 
part  produces  exaltation  of  its  sensibility ;  that  is,  the  ordinary  im- 
pressions produce  changes  of  unusual  energy  in  its  sensory  nerves. 
This  is  particularly  evident  in  the  increased  sensibility  of  the  genital 
organs  of  animals  during  the  period  of  heat;  and  in  those  of  Man, 
when  in  a  state  of  venereal  excitement.  Moderate  warmth,  friction, 
exercise,  and  other  causes  which  increase  the  circulation  through  a 
part,  also  augment  its  sensibility ;  and  this  augmentation  is  one  of  the 
most  constant  indications  of  that  state  of  determination  of  blood,  or 
active  congestion,  which  usually  precedes  inflammation,  and  which 
exists  in  the  parts  surrounding  the  centre  of  inflammatory  action. 
But  it  must  be  borne  in  mind,  here  as  elsewhere  (§  401),  that  such 
exaltation  of  function  in  a  limited  part,  is  quite  consistent  with  gene- 
ral debility  ;  and  in  fact  we  may  often  observe,  that  the  tendency  to 
such  local  aflfections  is  particularly  great,  when  the  blood  is  in  a  very 
poor  condition.    (See  Chap.  V.) 

405.  To  sum  up,  then,  we  may  compare  the  vesicular  substance, 
wherever  it  exists,  to  a  galvanic  combination  :  the  former  being  capa- 
ble of  generating  nervous  influence,  and  transmitting  it  along  the 
fibrous  structure,  to  the  part  on  which  it  is  to  operate ;  in  the  same 
manner  as  the  latter  generates  electric  power,  and  transmits  it  along 
the  conducting  wires,  to  the  point  at  which  it  is  to  effect  a  decompo- 
sition or  any  other  change.  In  one  of  the  most  perfect  forms  of  the 
galvanic  battery  (that  invented  by  Mr.  Smee),  although  the  metals 
remain  inserted  in  the  acid  solution,  and  are  consequently  always 
ready  for  action,  no  electricity  is  generated  until  the  circuit  is  com- 
plete; and  the  waste  of  the  zinc  produced  by  its  solution  in  the  acid, 
is  therefore  exactly  proportional  to  the  electric  effects  to  which  it  gives 
rise.  The  condition  of  the  nervous  system,  in  the  healthy  and  waking 
state,  bears  a  close  analogy  to  this ;  for  it  is  in  a  state  constantly  ready 
for  action,  but  waits  to  be  excited  ;  and  its  w^aste  is  proportional  to 
the  activity  of  its  function.  The  vesicular  matter,  diffused  over  the 
surface  of  the  body,  is  inactive,  until  an  impression  is  made  upon  it 
by  some  external  agent ;  but  a  change  then  takes  place  in  its  con- 
dition (of  which  we  know  no  more,  than  that  the  presence  of  arterial 

16 


242  CONNECTION  OF  NERVOUS  SYSTEM  WITH  MIND. 

blood  and  a  certain  amount  of  warmth  are  necessary  for  it),  which  is 
transmitted  to  the  central  organs  by  the  sensory  trunks.  It  would 
appear  that  the  excitement  of  this  change  has  a  tendency  to  increase 
the  afflux  of  blood  to  the  part ;  thus  when  a  lozenge  or  some  similar 
substance  is  allowed  to  lie  for  a  time  in  contact  with  the  tongue,  or 
with  the  side  of  the  mouth,  a  roughness  is  produced,  which  is  due  to 
the  erection  of  the  sensory  papillae,  by  the  distension  of  their  blood- 
vessels. On  the  other  hand,  the  change  in  the  vesicular  matter  of 
the  central  organs,  by  which  motion  is  produced  in  the  distant  mus- 
cles, may  be  excited  either  by  the  stimulus  conveyed  by  the  afferent 
nerves  (as  in  reflex  action,  §  392),  or  by  an  act  of  Mind.  This  act 
may  be  voluntary,  originating  in  the  will ;  or  it  may  be  instinctive  or 
emotional,  resulting  from  certain  states  of  mind  excited  by  sensations, 
and  altogether  independent  of  the  will.  Of  the  mode  in  which  the 
mind  thus  acts  upon  the  nervous  system,  we  know  nothing  whatever, 
and  probably  never  shall  be  informed  in  our  present  state  of  being. 
But  it  is  sufficient  for  us  to  be  aware  of  the  physiological  fact  of  the 
peculiar  connection  between  the  mind  and  the  brain  ;  a  connection  so 
intimate,  as  to  enable  the  mind  to  receive  through  the  body  a  know- 
ledge of  the  condition  of  the  Universe  around  it,  and  to  impress  on 
the  body  the  results  of  its  own  determinations ;  and  of  such  a  nature, 
that  the  regularity  of  the  working  of  the  mind  itself  is  dependent  upon 
the  complete  organization  of  the  brain  in  the  first  instance,  upon  the 
constant  supply  of  pure  and  well-elaborated  blood,  and  upon  all  those 
influences  which  favour  the  due  performance  of  the  nutritive  opera- 
tions in  general. 


BOOK   II. 

SPECIAL   PHYSIOLOGY. 


CHAPTER  IV. 

OF  FOOD,  AND  THE  DIGESTIVE  PROCESS. 

1 .  Sources  of  the  Demand  for  Jiliment, 

406.  The  dependence  of  all  Organized  beings  upon  food  or  aliment, 
must  be  evident  from  the  facts  stated  in  the  preceding  portion  of  this 
Treatise.  In  the  first  place,  the  germ  requires  a  large  and  constant 
supply  of  materials,  with  which  it  may  develop  itself  into  the  perfect 
being,  by  the  properties  with  which  it  is  endowed.  In  all  but  the 
lowest  tribes  of  Plants,  we  find  the  materials  required  for  the  earliest 
stages  of  the  process  prepared  and  set  apart  by  the  parent.  Thus  in 
the  seed^  the  germ  itself  forms  but  a  small  proportion  of  the  whole 
substance,  the  principal  mass  being  composed  of  starchy  matter,  which 
is  laid  up  there  for  its  nutrition ;  and  the  act  of  germination  consists 
in  the  appropriation  of  that  nutriment  by  the  germ,  and  the  consequent 
development  of  the  latter,  up  to  the  point  at  which  it  becomes  inde- 
pendent of  such  assistance,  and  is  able  for  itself  to  procure,  from  the 
soil  and  atmosphere  that  surround  it,  the  materials  for  its  continued 
growth.  So  in  the  egg  of  the  Animal,  the  principal  mass  is  composed 
of  Albumen  and  oily  matter;  the  germ  itself  being,  at  the  time  the 
egg  is  first  deposited,  a  mere  point  invisible  to  the  naked  eye  ;  these 
materials  serve  as  the  food  or  aliment  of  the  germ,  which  gradually 
draws  them  to  itself,  and  converts  them  into  the  materials  of  its  own 
structure,  and  at  the  end  of  a  certain  period  the  young  animal  comes 
forth  from  the  egg  ready  to  obtain  for  itself  the  food  which  is  neces- 
sary for  its  continued  increase  in  size. 

407.  In  many  instances  among  the  lower  animals,  the  form  in 
which  the  young  animal  emerges  from  the  egg  is  very  diflferent  from 
that  which  it  is  subsequently  to  assume;  and  the  latter  is  only  attained 
by  a  process  of  metamorphosis.  This  change  has  been  longest  known, 
and  most  fully  studied,  in  the  case  of  Insects  and  Frogs;  which 


244  SOURCES  OF  THE  DEMAND  FOR  ALIMENT. 

were  formerly  thought  to  constitute  an  exception  to  all  general  rules 
in  this  respect, — the  Insect  coming  forth  from  the  egg  in  the  state  of  a 
Worm,  and  the  Frog  in  the  condition  of  a  Fish.  But  it  is  now  known 
that  changes  of  form,  as  complete  as  these,  occur  in  a  large  propor- 
tion of  the  lower  tribes  of  Animals;  so  that  the  absence  of  them  is  the 
exception.  The  fact  seems  to  be,  that  the  supply  of  nutriment  laid 
up  within  the  egg,  among  the  lower  classes,  is  by  no  means  sufficient 
to  carry  on  the  embryo  to  the  form  it  is  subsequently  to  attain ;  and 
its  development  is  so  arranged  that  it  may  come  into  the  world  in  a 
condition  which  adapts  it  to  obtain  its  own  nutriment,  and  thus  to 
acquire  for  itself  the  materials  of  its  further  development.  Thusthe 
Insect,  in  its  larva  or  Caterpillar  state,  is  essentially  a  foetus  in  regard 
to  its  grade  of  development ;  but  it  is  a  foetus  capable  of  acquiring 
its  own  food.  In  this  condition  it  attains  its  full  growth  as  regards  size, 
though  its  form  remains  the  same  ;  but  it  then,  in  passing  into  the 
Chrysalis  state,  reassumes  (as  it  were)  the  condition  of  an  embryo 
within  the  egg,— the  development  of  various  new  parts  takes  place, 
at  the  expense  of  the  nutriment  stored  up  in  its  tissues, — and  it  comes 
forth  as  the  perfect  insect.  In  many  of  the  lower  tribes,  the  animal 
quits  the  egg  at  a  still  earlier  period  in  comparison ;  thus  it  has  been 
lately  shown  by  M.  Milne  Edwards,  that  some  of  the  long  marine 
worms  consist  only  of  a  single  segment,  forming  a  kind  of  head,  when 
they  leave  the  egg ;  and  that  the  other  segments,  to  the  number,  it 
may  be,  of  several  hundred,  are  gradually  developed  from  this,  by  a 
process  that  resembles  the  budding  of  Plants. 

408.  Up  to  the  period,  then,  when  the  full  dimensions  of  the  body 
have  been  attained,  and  the  complete  evolution  of  all  its  organs  has 
taken  place,  a  due  supply  of  food  is  necessary  for  these  purposes.  In 
the  Plant  nearly  the  whole  of  the  alimentary  materials  taken  into  the 
system,  are  thus  appropriated;  the  extension  of  its  structure  going  on 
almost  indefinitely,  and  the  waste  occasioned  by  decay  being  compara- 
tively small.  Thus  the  carbon,  which  is  given  out  by  the  respiratory 
process  in  the  form  of  carbonic  acid,  bears  but  a  small  proportion  to 
that,  which  is  introduced  by  the  decomposition  of  that  same  gas,  under 
the  influence  of  light  (§  81).  And  the  fall  of  the  leaves,  which  takes 
place  once  a  year  or  more  frequently,  and  which  gives  back  a  large 
quantity  of  the  matter  that  has  undergone  the  organizing  process,  does 
not  occur,  until  by  their  means  a  considerable  addition  has  been  made 
to  the  solid  and  permanent  substance  of  the  tree. 

409.  This  is  not  the  case,  however,  with  the  Animal.  Its  period 
of  increase  is  limited.  The  full  size  of  the  body  is  usually  attained, 
and  all  the  organs  acquire  their  complete  evolution  at  a  comparatively 
early  period.  The  continued  supply  of  food  is  not  then  requisite  for 
the  extension  of  the  structure,  but  simply  for  its  maintenance ;  and  the 
source  of  the  demand  lies  in  the  constant  waste,  to  which,  during  its 
period  of  activity,  it  is  subjected.  We  have  seen  that  every  action  of 
the  Nervous  and  Muscular  systems  involves  the  death  and  decay  of  a 
certain  amount  of  the  living  tissue, — as  indicated  by  the  appearance  of 


SOURCES  OF  DEMAND  FOR  FOOD.  245 

the  products  of  that  decay  in  the  Excretions;  and  a  large  part  of  the 
demand  for  food  will  be  consequently  occasioned  by  the  necessity  for 
making  good  the  loss  thus  sustained.  Hence  we  find  that  the  demand 
for  food  bears  a  close  relation  to  the  activity  of  the  animal  functions ; 
so  that  a  diet,  which  would  be  superfluous  and  injurious  to  an  indi- 
vidual of  inert  habits,  is  suitable  and  beneficial  to  one  who  is  leading 
a  life  of  continual  exertion;  and  this  diflference  manifests  itself  in  the 
requirements  of  the  same  individual  who  makes  a  change  in  his  habits, 
— the  indolent  man  acquiring  an  appetite  by  vigorous  exertion,  and 
the  active  man  losing  his  disposition  to  hearty  feeding  by  any  cause 
that  keeps  him  from  his  accustomed  exercise.  We  see  precisely  the 
same  contrast  between  Animals  of  different  tribes,  whose  natural 
instincts  lead  them  to  different  modes  of  life.  The  Birds  of  most 
active  flight,  and  the  Mammals  which  are  required  to  put  forth  the 
greatest  efforts  to  obtain  their  food,  need  the  largest  and  most  constant 
supplies  of  nutriment;  but  even  the  least  active  of  these  classes  stand 
in  remarkable  contrast  with  the  inert  Reptiles,  whose  slow  and  feeble 
movements  are  attended  with  so  little  waste,  that  they  can  sustain  life 
for  weeks  and  even  months,  with  little  or  no  diminution  of  their  usual 
activity,  without  a  fresh  supply  of  food. 

410.  The  waste  and  decay  just  adverted  to,  however,  do  not  affect 
the  muscular  and  nervous  tissues  alone ;  for  all  the  operations  of 
nutrition  involve  it  to  a  certain  extent.  It  has  been  already  shown 
that  the  acts  of  absorption,  assimilation,  respiration,  secretion,  and 
reproduction, — all  those,  in  fact,  by  which  the  material  for  the  nutri- 
tion of  the  nervous  and  muscular  tissues  is  first  prepared,  and  sub- 
sequently maintained  in  the  requisite  purity, — are  effected  in  the 
Animal,  as  in  the  Plant,  by  the  agency  of  cells,  which  are  continually 
dying  and  requiring  renewal.  In  most  Vegetables,  the  death  of  the 
parts  concerned  in  these  functions  takes  place  simultaneously,  as  soon 
as  they  have  performed  them ;  the  whole  crop  of  leaves  ceasing  at 
once  to  perform  its  proper  actions,  and  dropping  off; — to  be  replaced 
by  another,  at  an  interval  that  solely  depends  upon  the  temperature 
under  which  the  tree  is  living  (§  99).  In  the  evergreen,  however, 
the  process  bears  a  close  resemblance  to  that  which  we  observe  in 
the  Animal ;  for  the  leaves  die  one  by  one,  and  not  simultaneously ; 
and  are  constantly  undergoing  replacement,  so  that  the  vigour  of  the 
system  and  the  activity  of  its  nutritive  processes  never  suffer  a  com- 
plete suspension. 

411.  In  the  Animal  body,  the  different  classes  of  cells,  to  which 
allusion  has  been  made,  are  in  like  manner  constantly  undergoing 
death  and  renewal;  and  this  with  a  rapidity  proportioned  to  the 
energy  of  their  functions.  Hence  a  supply  of  food  is  as  requisite  to 
furnish  the  materials  of  their  growth,  as  it  is  in  Plants  to  furnish  the 
materials  of  the  growth  of  the  leaves.  A  large  part  of  these  materials 
are  subsequently  used  for  other  purposes  in  the  economy ;  thus,  as  the 
leaves  prepare  the  sap  which  is  to  nourish  the  woody  stem,  and  to 
form  new  shoots,  so  do  the  absorbing  and  assimilating  cells  prepare 


246  SOURCES  OF  DEMAND  FOR  FOOD. 

and  furnish  the  fluid  elements  of  the  blood,  which  are  to  repair  the 
waste  of  nerre  and  muscle,  bone  and  cartilage,  &c.  But  still  a  con- 
siderable amount  is  expended  in  the  simple  nutrition  of  these  organs 
themselves,  whose  duration  is  transient,  and  whose  solid  parts  are 
cast  off  as  of  no  further  use.  Thus  the  skin  and  all  the  mucous  sur- 
faces are  continually  forming  and  throwing  off  epidermic  and  epithelial 
cells,  whose  formation  requires  a  regular  supply  of  nutriment ;  and  only 
a  part  of  this  nutriment  (that  which  occupies  the  cavity  of  the  cells) 
consists  of  matter,  that  is  destined  to  serve  some  other  purpose  in  the 
system,  or  that  has  already  answered  it;  the  remainder  (that  of  which 
the  solid  walls  are  composed)  being  furnished  by  the  nutritive  mate- 
rials of  the  blood,  and  being  henceforth  altogether  lost  to  it. — Thus 
every  act  of  Nutrition  involves  a  waste  or  decay  of  Organized  tissue. 
412.  We  may  observe  a  marked  difference,  however,  between  the 
amount  of  aliment  required,  and  the  amount  of  waste  occasioned,  by 
the  simple  exercise  of  the  nutritive  or  vegetative  functions  in  the 
building-up  and  maintenance  of  the  animal  body,  and  that  which 
results  from  the  exercise  of  the  animal  functions.  The  former  are 
carried  on,  with  scarcely  any  intermixture  of  the  latter,  during  fcetal 
life.  The  aliment,  in  a  state  of  preparation,  is  introduced  into  the 
foetal  vessels;  and  is  conveyed  by  them  into  the  various  parts  of  the 
structure,  which  are  developed  at  its  expense.  The  amount  of  waste 
is  then  very  trifling,  as  we  may  judge  by  the  small  amount  of  excre- 
tory matter,  the  product  of  the  action  of  the  liver  and  kidneys,  w^hich 
has  accumulated  at  the  time  of  birth  ;  although  these  organs  have 
attained  a  sufficient  development  to  act  with  energy  when  called  upon 
to  do  so.  But  as  soon  as  the  movements  of  the  body  begin  to  take 
place  with  activity,  the  waste  increases  greatly ;  and  we  even  observe 
this  immediately  after  birth,  w-hen  a  large  part  of  the  time  is  still 
passed  in  sleep,  but  when  the  actions  of  respiration  involve  a  constant 
employment  of  muscular  power. — In  the  state  of  profound  sleep^  at 
subsequent  periods  of  life,  the  vegetative  functions  are  performed, 
with  no  other  exercise  of  the  animal  powers,  than  is  requisite  to  sus- 
tain them  ;  and  we  observe  that  the  w^aste,  and  the  demand  for  food, 
are  then  diminished  to  a  very  low  point.  This  is  well  seen  in  many 
animals,  which  lead  a  life  of  great  activity  during  the  warmer  parts 
of  the  year,  but  which  pass  the  winter  in  a  state  of  profound  sleep, 
without,  however,  any  considerable  reduction  of  temperature  ;  the 
demand  for  food,  instead  of  being  frequent,  is  only  felt  at  long  inter- 
vals, and  the  excretions  are  much  reduced  in  amount.  And  those 
animals  which  become  completely  inert,  either  by  the  influence  of 
cold,  or  by  the  drying-up  of  their  tissues,  do  not  suffer  from  the  pro- 
longed deprivation  of  food ;  because  not  only  are  their  animal  func- 
tions suspended,  but  their  nutritive  operations  also  are  in  complete 
abeyance  ;  and  the  continual  decomposition  of  their  tissues,  which 
would  otherwise  be  taking  place,  is  checked  by  the  cold  or  desicca- 
tion ;  so  that  the  whole  series  of  changes  which  goes  on  in  their  active 
condition  is  completely  at  a  stand. 


SOURCES  OF  DEMAND  FOR  FOOD.  247 

413.  But  there  is  another  most  important  cause  of  demand  for  food, 
amongst  the  higher  Animals,  which  does  not  exist  either  amongst  the 
lower  Animals,  or  in  the  Vegetable  kingdom.  We  have  seen  (Chap. 
II.)  that  Mammals  and  Birds,  and  to  a  certain  extent  Insects  also, 
are  able  to  sustain  the  heat  of  their  bodies  at  a  fixed  standard,  and 
thus  to  be  independent  of  variations  in  external  temperature.  This 
they  are  enabled  to  do,  as  will  be  explained  hereafter,  by  a  process 
strictly  analogous  to  ordinary  combustion ;  the  carbon  and  hydrogen 
directly  supplied  by  their  food,  or  after  having  been  employed  for  a 
time  in  the  composition  of  the  living  tissues  and  then  set  free,  being 
made  to  unite  with  oxygen  introduced  by  the  respiratory  process,  and 
thus  giving  off  the  same  heat  as  if  the  same  materials  were  burned 
in  a  furnace.  And  it  has  been  further  shown,  that  the  immediate 
cause  of  death  in  a  warm-blooded  animal,  from  which  food  has  been 
entirely  withheld,  is  the  inability  any  longer  to  sustain  the  temperature, 
which  is  requisite  for  the  performance  of  its  vital  operations  (§  117). 
Hence  we  see  the  necessity  for  a  constant  supply  of  aliment,  in  the 
case  of  warm-blooded  animals,  for  this  purpose  alone ;  and  the  de- 
mand will  be  chiefly  regulated  by  the  external  temperature.  When 
the  heat  is  rapidly  carried  off  from  the  surface,  by  the  chilling  influ- 
ence of  the  surrounding  air,  a  much  greater  amount  of  carbon  and 
hydrogen  must  be  consumed  within  the  body,  to  maintain  its  proper 
heat,  than  when  the  air  is  nearly  as  warm  as  the  body  itself;  so  that 
a  diet  which  is  appropriate  to  the  former  circumstances,  is  superfluous 
and  injurious  in  the  latter;  and  the  food  which  is  amply  sufficient  in 
a  warm  climate,  is  utterly  destitute  of  power  to  enable  it  to  resist  the 
influence  of  severe  cold.  This  is  a  fact  continually  experienced ; 
both  in  the  ordinary  recurrence  of  changes  of  temperature  in  our  own 
climate ;  and,  still  more  remarkably,  when  the  same  individual  is 
subjected  to  the  extremes  of  heat  and  cold,  in  successively  visiting 
the  tropical  and  frigid  zones. 

414.  Thus  we  find  that  in  the  Animal  body,  aliment  is  ordinarily 
required  for  four  different  purposes.  First,  for  the  original  construc- 
tion or  building-up  of  the  organism.  Second,  to  supply  the  loss  occa- 
sioned by  its  continual  decay,  even  when  in  a  state  of  repose.  Third, 
to  compensate  for  the  waste  occasioned  by  the  active  exercise  of  the 
nervous  and  muscular  systems.  And  Fourth,  to  supply  the  materials 
for  the  heat-producing  process,  by  which  the  temperature  of  the  body 
is  kept  up. — The  amount  required  for  these  several  purposes  will 
vary  according  to  the  conditions  of  the  body,  as  regards  exercise  or 
repose,  and  external  heat  or  cold.  It  is  also  subject  to  great  varia- 
tion with  difference  of  age.  During  the  period  of  growth,  it  might 
be  anticipated  that  a  larger  supply  of  food  would  be  required,  than 
when  the  full  stature  has  been  attained  ;  but  a  very  small  daily  addi- 
tion would  suffice  in  the  case  of  a  child  or  youth,  to  produce  the 
entire  increase  of  a  whole  year.  Yet  every  one  knows  that  the  child 
requires  much  more  food  than  the  adult,  in  proportion  to  his  compa- 
rative bulk.     This  results  from  the  much  more  rapid  change  in  the 


248  SOURCES  OF  DEMAND  FOR  FOOD. 

constituents  of  his  body;  which  is  evident  from  the  large  proportional 
amount  of  his  excretions,  from  the  quickness  with  which  the  effects 
of  illness  or  of  deficiency  of  food  manifest  themselves  in  the  diminu- 
tion of  the  bulk  and  firmness  of  the  body,  from  the  short  duration  of 
life  when  food  is  altogether  withheld,  and  from  the  readiness  with 
which  losses  of  substance  by  disease  or  injury  are  repaired,  when  the 
nutritive  processes  are  restored  to  their  full  activity.  The  converse 
of  all  this  holds  good  in  the  aged  person.  The  excretions  diminish 
in  amount,  the  want  of  food  may  be  sustained  for  a  longer  period, 
losses  of  substance  are  but  slowly  repaired,  and  everything  indicates 
that  the  interstitial  changes  are  performed  with  comparative  slowness; 
and,  accordingly,  the  demand  for  food  is  far  less  in  proportion  to  the 
bulk  of  the  body  than  it  is  in  the  adult,  and  may  be  even  absolutely 
less  than  in  the  child  of  a  fourth  of  its  weight. 

415.  The  demand  for  food  is  increased  by  any  cause,  which  creates 
an  unusual  di'ain  or  waste  in  the  system.  Thus  an  extensive  suppu- 
rating action  can  be  sustained  only  by  a  large  supply  of  highly-nutri- 
tious food.  The  mother,  who  has  to  furnish  the  daily  supply  of  milk 
w^hich  constitutes  the  sole  support  of  her  offspring,  needs  an  unusual 
sustenance  for  this  purpose.  And  there  are  states  of  the  system,  in 
which  the  solid  tissues  seem  to  possess  an  unusual  tendency  to  decom- 
position, and  in  which  an  increased  supply  of  aliment  is  therefore 
required.  This  is  the  case,  for  example,  in  diabetes ;  one  of  the  first 
symptoms  of  which  disease  is  the  craving  appetite,  that  seems  as  if  it 
would  never  be  satisfied.  And  there  can  be  no  doubt  that,  putting 
aside  all  the  other  circumstances  that  have  been  alluded  to,  there  is 
much  difference  amongst  individuals,  in  regard  to  the  rapidity  of  the 
changes  which  their  organism  undergoes,  and  the  amount  of  food 
required  for  its  maintenance. 

416.  The  influence  of  the  supply  of  food  upon  the  size  of  the  indi- 
vidual, is  very  evident  in  the  Vegetable  kingdom;  and  it  is  most 
strikingly  manifested,  when  a  plant  naturally  growing  in  a  poor  dry 
soil  is  transferred  to  a  damp  rich  one,  or  when  we  contrast  two  or 
more  individuals  of  the  same  species,  growing  in  localities  of  opposite 
characters.  Thus,  says  Mr.  Ward,  "  I  have  gathered,  on  the  chalky 
borders  of  a  wood  in  Kent,  perfect  specimens  in  full  flower  of  Ery- 
thrcea  Centaurium  (Common  Centaury),  not  more  than  half  an  inch 
in  height ;  consisting  of  one  or  two  pairs  of  most  minute  leaves,  with 
one  solitary  flower :  these  were  growing  on  the  bare  chalk.  By  trac- 
ing the  plant  towards  and  in  the  wood,  I  found  it  gradually  increasing 
in  size,  until  its  full  development  was  attained  in  the  open  parts  of 
the  wood,  where  it  became  a  glorious  plant  four  or  five  feet  in  eleva- 
tion, and  covered  with  hundreds  of  flowers."  On  the  other  hand,  by 
starvation,  naturally  or  artificially  induced.  Plants  may  be  dwarfed, 
or  reduced  in  stature  :  thus  the  Dahlia  has  been  diminished  from  six 
feet  to  two  ;  the  Spruce  Fur  from  a  lofty  tree  to  a  pigmy  bush  ;  and 
many  of  the  trees  of  plains  become  more  and  more  dwarfish  as  they 
ascend  mountains,  till  at  length  they  exist  as  mere  underwood.    Part 


INFLUENCE  OF  VARIATIONS  IN  SUPPLY  OF  FOOD.      249 

of  this  effect,  however,  is  doubtless  to  be  attributed  to  diminished 
temperature ;  which,  as  already  remarked,  concurs  with  deficiency  of 
food  in  producing  inferiority  of  size. 

417.  Variations  in  the  supply  of  food  would  not  appear  to  Ije 
effectual  in  producing  a  corresponding  variety  of  size  in  the  Animal 
kingdom  :  this  is  not,  however,  because  Animals  are  in  any  degree 
less  dependent  than  Plants  upon  a  due  supply  of  food ;  but  because 
such  a  limitation  of  the  supply,  as  would  dwarf  a  Plant  to  any  con- 
siderable extent,  would  be  fatal  to  the  life  of  an  Animal.  On  the 
other  hand,  an  excess  of  food,  which  (under  favourable  circum- 
stances) would  produce  great  increase  in  the  size  of  the  Plant,  would 
have  no  corresponding  influence  on  the  Animal ;  for  its  size  appears 
to  be  restrained  within  much  narrower  limits, — its  period  of  growth 
being  restricted  to  the  early  part  of  its  life,  and  the  dimensions  proper 
to  the  species  being  rarely  exceeded  in  any  great  degree.  Even  in 
the  case  of  giant  individuals,  it  does  not  appear  that  the  excess  of 
size  is  produced  by  an  over-supply  of  food ;  but  that  the  larger  sup- 
ply of  food  taken  in  is^  called  for  by  the  unusual  wants  of  the  system, 
— those  wants  being  the  result  of  an  extraordinary  activity  in  the  pro- 
cesses of  growth,  and  being  traceable  rather  to  the  properties  inherent 
in  the  system,  than  to  any  external  agencies.  Thus  we  not  unfre- 
quently  hear  of  children,  who  have  attained  an  extraordinary  size  at 
the  age  of  a  few  years  ;  and  this  excess  of  size  is  usually  accompanied 
with  other  marks  of  precocious  development.  We  shall  hereafter  see, 
that  a  provision  exists  in  the  Digestive  apparatus,  which  absolutely 
prevents  the  reduction  and  preparation  of  the  food,  in  any  amount 
greatly  surpassing  that  which  the  wants  of  the  system  demand  (§  474) ; 
and  it  is  probably  to  this  cause,  in  part,  that  we  are  to  attribute  the 
small  degree  of  influence  exerted  by  an  excess  of  food,  in  producing 
an  increased  development  of  the  Animal  frame. 

418.  The  influence  of  a  diminished  supply  of  food,  in  producing  a 
marked  inferiority  in  the  size  of  Animals,  is  most  effectually  exerted 
during  those  early  periods  of  growth,  in  which  the  condition  of  the 
system  is  most  purely  Vegetative.  Thus  it  is  well  known  to  Ento- 
mologists, that,  whilst  it  is  rare  to  find  Insects  departing  widely  from 
the  average  size  on  the  side  of  excess,  dwarf-individuals,  possessing 
only  half  the  usual  dimensions,  or  even  less,  are  not  uncommon  ;  and 
there  can  be  little  doubt  that  these  have  suffered  from  a  diminished 
supply  of  nutriment  during  their  larva  state.  This  variation  is  most 
apt  to  present  itself  in  the  very  large  species  of  Beetles,  which  pass 
several  years  in  the  larva  state  ;  and  such  dwarf- specimens  have  even 
been  ranked  as  sub-species.  Abstinence  has  been  observed  to  pro- 
duce the  effect,  upon  some  Caterpillars,  of  diminishing  the  number  of 
moults  and  accelerating  the  transformation ;  in  such  cases,  the  Chry- 
salis is  more  delicate,  and  the  size  of  the  perfect  Insect  much  below 
the  average. 

419.  One  of  the  most  remarkable  examples  known,  of  the  effect  of 
food  in  modifying  the  development  of  Animals,  is  to  be  found  in  the 


250      INFLUENCE  OF  VARIATIONS  IN  SUPPLY  OF  FOOD. 

economy  of  the  Hive-Bee.  In  every  community,  the  majority  of 
Individuals  consists  of  neuters ;  which  may  be  regarded  as  females, 
having  the  organs  of  the  female  sex  undeveloped ;  and  which,  whilst 
iHcapable  of  reproduction,  perform  all  the  labours  of  the  hive.  The 
office  of  continuing  the  race  is  restricted  to  the  queen ;  who  is  the 
only  perfect  female  in  the  community.  If  by  any  accident  the  queen 
be  destroyed,  or  if  she  be  purposely  removed  for  the  sake  of  experi- 
ment, the  bees  choose  two  or  three  from  amongst  the  neuter  eggSy 
which  have  been  deposited  in  their  appropriate  cells ;  and  these  they 
cause  to  be  developed  into  perfect  queens.  The  first  operation  is  to 
change  the  cells  in  which  they  lie  into  royal  cells  ;  these  differ  con- 
siderably from  the  ordinary  ones  in  form,  and  are  of  much  larger 
dimensions.  This  is  accomplished  by  breaking  down  the  walls  of 
the  surrounding  cells,  removing  the  eggs  or  grubs  they  may  contain, 
and  rebuilding  the  central  upon  an  enlarged  scale,  and  upon  the  same 
plan  as  the  royal  cells  in  which  the  queens  are  ordinjirily  reared. 
When  the  eggs  are  hatched,  the  maggot  is  supplied  with  food  of  a 
very  different  nature  from  the  farina  or  bee-bread  (composed  of  a 
mixture  of  pollen  and  honey)  which  has  been  stored  up  for  the  nourish- 
ment of  the  workers :  this  food  being  of  a  jelly-like  consistence  and 
pungent,  stimulating  character.  After  the  usual  transformations,  the 
grub  becomes  a  perfect  queen  ;  differing  from  the  neuter  bee,  into 
which  it  would  otherwise  have  been  changed,  not  only  in  the  develop- 
ment of  the  reproductive  system,  but  in  the  general  form  of  the  body, 
the  proportionate  shortness  of  the  wings,  the  shape  of  the  tongue, 
jaws,  and  sting,  the  absence  of  the  hollows  on  the  thighs  in  which 
the  pollen  is  carried,  and  the  loss  of  the  power  of  secreting  wax. 

420.  That  insufficiency  of  wholesome  food,  continued  through  suc- 
cessive generations,  may  produce  a  marked  effect,  not  merely  upon 
the  stature,  but  upon  the  form  and  condition  of  the  body,  even  in  the 
Human  race,  appears  from  many  cases,  in  which  such  influence  has 
operated  on  an  extensive  scale.  Thus  there  are  parts  of  Ireland 
inhabited  by  a  population  descended  from  those  who  were  treated 
by  the  English  as  rebels  two  centuries  since,  and  who  were  driven 
into  mountainous  tracts,  bordering  the  sea,  where  they  have  been 
since  exposed  to  the  two  great  brutalizers  of  the  human  race, 
hunger  and  ignorance.  The  present  race  is  distinguished  physically 
from  the  kindred  race  of  Meath  and  other  neighbouring  districts, 
where  the  same  causes  have  not  been  in  operation,  by  their  low  stature 
(not  exceeding  five  feet  two  inches),  their  pot-bellies  and  bow-legs; 
whilst  their  open  projecting  mouths,  with  prominent  teeth  and  exposed 
gums,  their  advancing  cheek-bones  and  depressed  noses,  bear  bar- 
barism in  their  very  front.  "  These  spectres  of  a  people  that  once 
were  well-grown,  able-bodied,  and  comely,  stalk  abroad  into  the 
daylight  of  civilization,  the  animal  apparitions  of  Irish  ugliness  and 
Irish  want." — The  whole  aboriginal  population  of  New  Holland  pre- 
sents a  similar  aspect ;  and  apparently  from  the  operation  of  the  same 
causes. 


EFFECTS  OF  EXCESS  OF  FOOD.  251 

421.  When  a  larger  quantity  of  food  is  habitually  consumed  than 
the  wants  of  the  system  require,  it  is  not  converted  into  solid  flesh ; 
but  it  is  got  rid  of  by  the  various  processes  of  excretion.  The  in- 
creased production  of  Muscular  fibre  depends,  as  we  have  already 
seen  (§  362),  upon  nothing  so  much  as  the  exercise  of  the  muscle.  It 
cannot  take  place,  unless  the  blood  supply  it  with  the  materials  :  but  no 
degree  of  richness  of  the  blood  can  alone  produce  it.  Consequently, 
the  accumulation  of  nutritive  matter  in  the  blood  is  so  far  from  being 
a  condition  of  healthy  that  it  powerfully  tends  to  produce  disease, — 
either  of  an  inflammatory  character,  if  the  fibrin  predominate, — or  of 
the  hemorrhagic  character,  if  the  red  corpuscles  predominate.  This 
state  is  most  apt  to  present  itself  in  those  who  live  well  and  take  little 
exercise  ;  and  the  remedy  for  it  is  either  to  diminish  the  diet,  or  to 
increase  the  amount  of  exercise,  so  as  to  brfng  the  two  into  harmony. 

422.  The  continued  over-supply  of  food  has  several  injurious  effects; 
it  disorders  the  digestive  processes,  by  stimulating  them  to  undue 
activity,  and  lays  the  foundation  for  a  complete  derangement  of  them  ; 
it  gives  a  predisposition  to  the  various  diseases  of  repletion,  as  already 
noticed ;  and  it  throws  upon  the  excreting  organs  much  more  than 
their  proper  amount  of  labour,  besides  tending  to  produce  a  depraved 
condition  of  the  matters  to  be  drawn  off  by  them,  which  renders  the 
proper  act  of  excretion  still  more  difficult.  When  this  is  the  case, 
various  disorders  arise,  caused  by  the  retention,  within  the  circulating 
current,  of  substances  which  are  very  noxious  to  the  general  system, 
and  which  become  most  fertile  sources  of  disease.  What  are  com- 
monly regarded  as  diseases  of  the  biliary  and  urinary  organs,  are 
really,  in  a  large  proportion  of  cases,  nothing  else  than  disordered 
actions  of  these  organs,  occasioned  by  the  irregular  mode  in  w^hich 
the  products  of  decomposition  are  formed  within  the  blood,  and  de- 
pendent upon  some  error  in  diet,  either  as  regards  quantity  or  quality. 
Thus  the  "  lithic  acid  diathesis,"  in  which  there  is  an  undue  propor- 
tion of  that  substance  in  the  urine,  and  of  which  Gout  is  a  particular 
manifestation,  is  due,  not  to  disorder  of  the  kidney,  but  to  an  undue 
production  of  lithic  acid  in  the  blood  ;  so  long  as  the  excreting  action 
of  the  kidney  is  sufficient  to  prevent  its  accumulation  in  the  blood,  so 
long  the  general  health  is  but  little  affected  ;  but  whenever  that  action 
receives  a  check,  various  constitutional  symptoms  indicate  that  the 
system  is  disturbed  by  the  presence  of  this  product  of  decomposition. 
And  though  our  remedies  may  be  rightly  directed,  in  part,  to  facili- 
tating its  escape  through  the  kidneys,  yet  the  radical  cure  is  to  be 
sought  only  in  the  regulation  of  the  diet,  and  in  the  prevention  of  the 
first  production  of  the  substance  in  question. — Similar  remarks  might 
probably  be  applied  to  disorders  of  the  Liver;  but  we  are,  from 
various  causes,  far  less  perfectly  acquainted  with  their  character  than 
we  are  with  those  of  the  Kidney. 

423.  There  is  only  one  tissue,  the  increase  of  which  is  directly 
produced  by  an  over-supply  of  food.  This  is  the  Adipose  or  fatty. 
It  is  formed  almost  entirely  at  the  expense  of  the  non-azotized  con" 


252      INFLUENCE  OF  FOOD  UPON  PRODUCTION  OF  FAT. 

stituents  of  the  food ;  the  walls  of  the  cells,  into  which  the  fatty 
matter  is  secreted,  being  the  only  part  of  this  tissue  that  is  derived 
from  the  proteine-compounds  of  the  blood.  The  production  of  the 
adipose  tissue  is  most  directly  favoured  by  the  presence  of  a  large 
amount  of  fatty  matter  in  the  food ;  but  it  may  also  take  place,  as 
will  be  presently  shown,  by  the  conversion  of  starchy  and  saccharine 
substances  into  fatty  compounds.  It  cannot  occur,  unless  there  be  in 
the  food  a  larger  proportion  of  substances  that  can  be  thus  appro- 
priated, than  is  sufficient  to  maintain  the  heat  of  the  system  by  the 
respiratory  process.  .Consequently,  whatever  increases  the  demand 
for  heat,  is  unfavourable  to  the  deposition  of  fat;  and  vice  versa.  The 
fattening  of  animals  is  now  brought  to  a  regular  system  ;  and  expe- 
rience has  shown  that  rest  and  a  warm  temperature,  with  food  con- 
taining a  large  amount  of* oily  matter,  are  most  conducive  to  the  accu- 
mulation. Rest  acts  by  keeping  the  respiration  at  a  low  standard  ; 
for  it  will  hereafter  be  shown  (Chap.  VIII.),  that  a  much  larger  pro- 
portion of  carbonic  acid  is  thrown  off  when  the  body  is  in  active 
movement,  than  when  it  is  in  repose.  External  warmth  has  the  same 
effect;  the  demand  upon  the  calorifying  power  being  diminished,  and 
more  of  the  combustible  material  being  left,  to  be  stored  up  as  fat. 

424.  The  deposition  of  fat  affords  a  supply  of  combustible  matter, 
against  the  time  when  it  may  be  needed  ;  and  it  is  consequently  found, 
that  the  duration  of  life  in  warm-blooded  animals,  when  they  are  com- 
pletely deprived  of  food,  is  in  great  degree  proportional  to  the  amount 
of  fat  they  have  previously  accumulated.  There  is  no  sufficient 
reason  to  believe  that  fatty  matter  can  be  converted,  within  the  ani- 
mal body,  into  a  proteine-compound,  which  can  serve  for  the  nutri- 
tion of  the  muscular  and  other  tissues.  But  the  greatest  and  most 
constant  waste,  when  an  animal  is  undergoing  starvation,  is  that  which 
is  occasioned  by  the  heat-producing  process  ;  this,  so  long  as  the  sup- 
ply lasts,  is  kept  up  by  the  store  of  fat,  which  is  gradually  consumed  ; 
and  when  it  is  completely  exhausted,  the  temperature  falls,  hour  by 
hour,  until  life  can  no  longer  be  sustained,  (§  117).  The  use  of  this 
store  of  fat,  in  supplying  any  temporary  deficiency  in  the  food,  be- 
comes evident  from  such  experiments ;  for  when  it  has  been  com- 
pletely exhausted,  the  withholding  of  a  single  meal  proves  fatal,  from 
the  want  of  power  to  sustain  the  calorifying  process.  We  find  that 
animals,  which  are  likely  to  suffer  from  deficiency  of  food  in  the  winter, 
or  which  spend  that  period  in  a  state  of  quiescence,  have  a  tendency 
to  accumulate  a  store  of  fat  in  the  autumn  ;  which  tendency  seems 
principally  to  depend  upon  the  nature  of  their  food.  We  observe  it 
chiefly  in  those  Birds  and  Mammals  which  live  upon  seeds  and  grains ; 
and  these,  when  ripe,  contain  a  large  quantity  of  oily  matter,  which 
thus  becomes  a  valuable  store  against  the  time  of  need.  There  are 
many  birds,  such  as  the  beccafico  so  much  esteemed  in  Italy,  which 
are  described,  if  killed  at  this  season,  as  being  "  lumps  of  fat." 

425.  It  is  well  known  to  breeders  of  cattle,  that  some  varieties  or 
breeds  have  a  much  greater  tendency  to  the  production  of  Adipose 


VALUE  OF  DIFFERENT  MATERIALS  OF  FOOD.  253 

tissue,  than  others  placed  under  the  same  circumstances ;  and  the 
former  are  therefore  selected  to  undergo  the  fattening  process.  Cor- 
responding differences  may  be  met  with  among  different  individuals 
of  the  Human  race  ;  some  persons  having  a  remarkable  tendency  to 
the  production  of  fat,  under  circumstances  which  do  not  seem  by  any 
means  favourable  to  it,  whilst  others  appear  as  much  indisposed  to  this 
deposit.  The  latter  condition  we  notice  particularly  in  that  temperament 
which  is  commonly  termed  the  "  bilious ;"  and  it  is  important  to  bear  in 
mind  that,  where  such  an  indisposition  exists,  any  superfluity  of  fatty 
matter  in  the  food  taken  into  the  system,  must  be  excreted  again  through 
the  liver,  instead  of  being  retained  and  stored  up  in  the  body.  It  is 
very  desirable,  therefore,  that  such  persons  should  abstain  from  any 
excess  of  this  kind ;  since  an  habitual  call  upon  the  liver,  to  relieve 
the  system  of  a  superfluity  of  fatty  matter,  is  certain  to  produce  a  dis- 
ordered state  of  that  organ;  and  in  order  to  prevent  it,  the  diet  should 
be  altered  so  as  to  include  less  of  fatty  matter,  or  the  amount  of  exer- 
cise should  be  increased,  so  that  it  may  be  burned  off  by  the  addi- 
tional respiration  which  then  takes  place. 

426.  We  see,  then,  that  the  amount  of  food  which  can  be  properly 
appropriated  by  the  system  varies  considerably  in  different  individuals, 
and  in  the  same  individual  under  different  circumstances.  Conse- 
quently it  is  impossible  to  give  any  general  rule,  which  shall  apply  to 
every  one  alike.  The  average  quantity  required  by  adult  men,  leading 
an  active  life,  and  exposed  to  the  ordinary  vicissitudes  of  temperature 
in  our  own  climate,  seems  to  be  from  30  to  36  ounces  of  dry  aliment. 
But  a  healthy  condition  may  be  kept  up  on  scarcely  more  than  half 
this  allowance,  if  the  muscular  powers  are  but  little  exerted,  and  the 
surrounding  temperature  be  high;  provided  that  it  consist  of  sub- 
stances of  a  nutritious  kind,  united  in  proper  proportions. 

427.  The  value  of  different  substances  as  aliment,  depends  in  the 
first  place  upon  the  quantity  of  solid  matter  they  contain ;  being  of 
course  the  greater,  as  the  solids  form  the  larger  proportion  of  the  entire 
weight.  Many  esculent  vegetables  contain  so  large  a  quantity  of 
water,  that  the  nutriment  they  afford  is  very  slight  in  proportion  to 
their  bulk. — Next  it  depends  upon  the  proportion  of  digestible  matter 
which  the  solid  parts  include ;  for  it  is  not  every  substance  containing 
the  requisite  ingredients,  that  is  capable  of  being  reduced  to  a  state 
which  enables  it  to  be  absorbed.  Thus  woody  fibre  is  composed  of  the 
same  elements  as  starch-gum ;  but  it  passes  out  of  the  intestinal  canal 
unchanged,  and  therefore  affords  no  nutriment.  In  the  same  manner, 
the  horny  tissues  of  animals,  though  nearly  allied  to  proteine  in  their 
composition,  are  completely  destitute  of  nutritive  properties  to  Man 
and  the  higher  animals,  because  not  capable  of  being  reduced  by  their 
digestive  process;  though  certain  insects  appear  capable  of  living 
exclusively  upon  them. 

428.  But  when  the  watery  and  indigestible  parts  of  the  food  are 
put  out  of  consideration,  and  our  attention  is  directed  only  to  the 
soluble  solids,  we  find  a  most  important  difference  in  the  chemical 


254  VALUE  OF  DIFFERENT  MATERIALS  OF  FOOD. 

composition  of  different  substances,  -which  renders  them  more  or  less 
appropriate  to  the  different  purposes  which  have  to  be  answered  in  the 
nutrition  of  the  body.  It  has  been  already  pointed  out,  that  Vege- 
tables possess  the  power  of  combining  the  elements  furnished  by  the 
inorganic  world  into  two  classes  of  compounds, — the  ternary,  consist- 
ing of  oxygen,  hydrogen,  and  carbon, — and  the  quarternary,  which 
consists  of  these  elements,  with  the  addition  of  azote  or  nitrogen. 
These  two  classes  are  hence  termed  the  non-azotized  and  the  azotized. 

429.  Now  the  azotized  compounds  which  are  formed  by  Plants,  are 
essentially  the  same  with  those  which  are  furnished  by  the  flesh  and 
by  the  albuminous  fluids  of  Animals,  as  already  shown  (§  169);  and 
these  are  required  for  the  reparation  of  the  waste  of  the  muscular 
tissue  and  for  the  general  nutrition  of  the  body.  Consequently,  unless 
the  food  contain  a  sufficient  proportion  of  these  substances,  the  body 
must  be  insufficiently  nourished,  and  the  strength  must  diminish,  even 
though  other  elements  of  the  food  be  in  superabundance.  The  other 
azotized  compounds  existing  in  the  animal  body  may  be  elaborated 
by  the  transformation  of  these  proteine-compounds ;  so  that  when  they 
are  duly  supplied,  the  system  cannot  become  enfeebled  for  want  of 
support. — But  there  is  another  azotized  compound,  Gelatin,  that  is 
furnished  by  Animals,  to  which  nothing  analogous  exists  in  Plants ; 
and  this,  although  it  cannot  sustain  life  by  itself,  is  a  valuable  adjunct 
to  the  proteine  compounds.  For  as  the  gelatinous  tissues  suffer  waste 
in  common  with  the  others,  it  is  evident  that  if  the  gelatin  be  sup- 
plied already  prepared,  it  may  be  at  once  applied  to  their  nutrition ; 
and  thus  the  proportion  of  proteine,  which  they  would  otherwise  re- 
quire, is  not  demanded,  and  the  labour  of  transformation  is  also  saved. 
Further,  there  is  this  great  advantage  in  combining  a  proportion  of 
gelatin  with  the  food, — especially  when  the  digestive  powers  are 
feeble, — that  being  already  in  a  state  of  perfect  solution,  it  is  taken  up 
at  once  by  the  simple  act  of  physical  absorption  or  endormose,  instead 
of  requiring  the  selective  absorption,  which  involves  an  act  of  cell- 
formation  (§  494).  But  there  is  no  evidence  that  gelatin  can  ever 
be  transformed  into  a  proteine-corapound,  and  can  thus  be  applied  to 
the  nutrition  of  the  muscular  and  other  fibrous  tissues ;  and  the  pre- 
sumption, derived  from  the  results  of  various  experiments,  is  very 
strong  the  other  way. 

430.  The  quantity  of  azotized  substances  furnished  by  Plants  is 
usually  small  in  proportion  to  that  of  the  non-azotized ;  being  consider- 
able only  in  the  Corn-grains,  and  in  the  seeds  of  Leguminous  plants, 
which  the  universal  experience  of  ages  has  demonstrated  to  be  the 
most  nutritious  of  Vegetable  substances.  The  non-azotized  compounds 
exist  under  various  forms ;  of  which  the  principal  are  starch,  sugar, 
and  oil.  The  two  former  may  be  regarded  as  belonging  to  one  class ; 
because  we. know  that  starch  and  the  substances  allied  to  it  maybe 
converted  into  sugar  by  simple  chemical  processes,  and  that  this  trans- 
formation takes  place  readily  both  in  the  Vegetable  and  Animal  econo- 
my.    On  the  other  hand,  the  oily  matters  contained  in  vegetable  and 


VALUE  OF  DIFFERENT  MATERIALS  OF  FOOD.  255 

animal  food,  are  usually  ranked  as  a  distinct  group  of  alimentary  sub- 
stances ;  and  it  has  been  maintained  that,  under  no  circumstances,  has 
the  Animal  the  power  of  elaborating  fatty  matter  from  starchy  or  sac- 
charine cbmpounds.  But  this  is  now  known  to  be  an  unfounded  limi- 
tation ;  since  the  transformation  of  a  saccharine  into  a  fatty  compound 
takes  place  in  the  case  of  bees,  which  form  wax  when  fed  upon  pure 
sugar ;  and  it  has  been  recently  shown  that  it  may  take  place  in  the 
laboratory  of  the  Chemist,  butyric  acid  (the  fatty  acid  of  rancid  butter) 
being  one  of  the  products  of  the  fermentation  of  sugar  taking  place 
under  peculiar  circumstances. 

431.  The  great  use  of  these  substances  in  the  Animal  economy,  is 
to  support  the  respiratory  process,  and  thus  maintain  the  temperature 
of  the  body.  We  have  seen  that,  in  the  compounds  of  the  Saccharine 
group  (in  which  Starch  is  included)  the  amount  of  oxygen  is  no  more 
than  sufficient  to  form  water  with  the  hydrogen  of  the  substance  (§  12); 
so  that  the  carbon  is  free  to  combine  with  the  oxygen  taken  in  by  the 
lungs,  and  thus  becomes  a  source  of  calorifying  power.  Again,  in 
the  oily  matters  taken  in  as  food,  the  proportion  of  oxygen  is  far 
smaller ;  so  that  they  contain  a  large  quantity  of  surplus  hydrogen, 
as  well  as  of  carbon,  ready  to  be  burned  off  in  the  system,  and  thus 
to  supply  the  heat  required.  This  is  obviously  the  ordinary  destina- 
tion of  the  alimentary  matters  belonging  to  these  classes ;  and  the 
greatest  economy  in  the  choice  of  diet  is  therefore  exercised,  when  it 
is  composed  of  azotized  substances  in  sufficient  amount  to  repair  the 
waste  of  the  system,  and  of  non-azotized  compounds  which  include 
free  carbon  and  hydrogen  in  sufficient  quantity  to  develop  (with  the 
aid  of  other  processes)  the  requisite  amount  of  heat  by  combination 
with  oxygen.  But  if  there  be  a  deficiency  in  either  of  these  kinds 
of  aliment,  the  body  must  suffer.  Should  the  supply  of  duly-prepared 
azotized  matter  be  less  than  is  required  to  repair  the  waste  of  the 
albuminous  and  gelatinous  tissues,  then  these  diminish  in  bulk  and 
in  vital  power,  though  the  heat  of  the  body  may  be  kept  up  to  its 
proper  standard.  But  if  the  non-azotized  matter  would  be  supplied 
in  sufficient  amount,  or  in  a  form  in  which  it  cannot  be  appropriated, 
the  heat  of  the  body  cannot  be  sustained  in  any  other  way  than  by 
drawing  upon  the  store  of  fat  previously  laid  up. 

432.  Various  circumstances  lead  to  the  belief,  that  the  saccharine 
compounds  are  thus  carried  off  by  the  respiratory  process,  within  a 
short  time  after  they  have  been  introduced  into  the  system.  They 
have  not  been  detected  in  the  chyle  drawn  from  the  lacteal  absorbents ; 
but  there  seems  reason  to  believe  that,  in  consequence  of  their  ready 
solubility,  they  are  directly  taken  up  by  the  blood  (§  493),  and  that 
they  are  so  rapidly  burned  off  there,  as  to  escape  notice  in  that  fluid. 
But  it  has  been  lately  shown  by  Dr.  Buchanan,  that,  if  the  blood  be 
examined  within  a  short  time  after  a  meal  consisting  in  part  of  fari- 
naceous and  saccharine  substances,  a  very  appreciable  quantity  of 
saccharine  matter  is  found  in  it.  This  soon  disappears,  however ; 
being  eliminated  or  separated  from  the  blood  by  the  action  of  the 


256  VALUE  OF  DIFFERENT  MATERIALS  OF  FOOD. 

lungs.  In  fact  it  is  very  probable,  that  a  large  proportion  of  the  mat- 
ter thus  taken  in  never  enters  the  general  circulation  at  all ;  as  the 
blood  of  the  mesenteric  veins  proceeds  to  the  lungs,  after  passing 
through  the  liver,  before  it  is  transmitted  to  the  systemic  arteries,  and 
may  there  lose  its  saccharine  matter,  as  fast  as  this  is  taken  in  from 
the  stomach.  After  a  meal  containing  the  ordinary  admixture  of  sac- 
charine, oily,  and  albuminous  compounds,  it  is  probable  that  the  sac- 
charine are  first  received  into  the  blood,  and  are  the  first  to  be  elimi- 
nated from  it ;  and  that,  by  the  time  they  have  been  all  consumed, 
the  oily  matter,  introduced  through  the  more  circuitous  channel  of  the 
lacteal  system,  is  ready  to  answer  the  same  purpose.  If  these  are 
exhausted  before  a  fresh  supply  of  food  is  taken  in,  cold  as  well  as 
hunger  is  experienced ;  and  the  body  is  in  this  condition  peculiarly 
liable  to  suffer  from  any  depressing  causes,  such  as  a  low  external 
temperature,  poisonous  miasmata,  &c.;  hence  the  prudence  of  avoid- 
ing exposure  to  such  influences  upon  an  empty  stomach. 

433.  We  can  thus  in  part  account  for  the  fact,  which  universal 
experience  has  established,  that  in  warm-blooded  animals,  a  mixture 
of  azotized  and  non-azotized  substances  is  the  diet  most  conducive 
to  the  welfare  of  the  body  ;  and  that,  in  all  but  the  purely  carnivorous 
tribes,  the  diet  provided  by  Nature  consists  not  only  of  albuminous, 
gelatinous,  and  oily  substances,  such  as  are  furnished  by  the  flesh  and 
fat  of  animals,  but  also  of  saccharine  or  farinaceous  matter.  This  is 
the  diet  to  which  Man  is  evidently  best  adapted  ;  and  it  is  remarkable 
how  completely  accordant  is  his  use  of  the  ordinary  materials  of  food, 
"with  the  principles  now  established  by  chemical  and  physiological 
research,  in  regard  to  the  wants  of  his  bodily  system,  and  the  best 
mode  of  supplying  them.  Thus,  good  wheaten  bread  contains,  more 
nearly  than  any  other  substance  in  ordinary  use,  that  proportion  of 
azotized  and  non-azotized  matter,  which  is  adapted  to  repair  the 
waste  of  the  system,  and  to  supply  the  necessary  amount  of  combus- 
tible material,  under  the  ordinary  conditions  of  civilized  life  in  tem- 
perate climates;  and  we  find  that  the  health  and  strength  can  be  more 
perfectly  sustained  upon  that  substance,  than  upon  any  other  taken 
alone.  The  addition  of  a  moderate  quantity  of  butter  increases  its 
heat-producing  powers ;  and  this  is  especially  useful  when  the  tem- 
perature is  low, — under  which  condition,  there  is  usually  an  increased 
disposition  to  the  employment  of  fatty  matters  as  articles  of  food.  On 
the  other  hand,  if  the  body  be  subject  to  violent  exertion,  advantage 
is  gained  by  increasing  the  proportion  of  the  proteine-compounds,  by 
the  addition  of  animal  flesh;  and,  under  any  circumstances,  there  is 
an  economy  in  the  use  of  gelatin,  in  the  form  of  soup,  which  dimin- 
ishes the  demand  for  other  azotized  matter.  The  use  of  animal 
flesh,  however,  as  a  principal  article  of  diet,  except  when  the  indi- 
vidual is  leading  the  incessantly-active  life  of  a  carnivorous  animal, 
is  very  far  from  being  economical,  and  is  positively  injurious  to  the 
welfare  of  the  body. 

434.  On  the  other  hand,  in  rice,  potatoes,  casava-meal,  and  simi- 


VALUE  OF  DIFFERENT  MATERIALS  OF  FOOD.  257 

lar  substances,  the  farinaceous  or  saccharine  components  form  so  very 
large  a  proportion  of  the  whole  mass,  and  the  proteine-compounds  are 
present  in  so  very  small  an  amount,  that  they  are  insufficient  to  sup- 
port the  bodily  vigour  when  taken  alone,  unless  a  larger  quantity  be 
ingested,  so  as  to  supply  the  requisite  proportion  of  azotized  matter. 
But  when  these  substances  form  part  of  a  mixed  diet,  the  other  ingre- 
dient of  which  consists  of  animal  flesh,  a  much  smaller  quantity  of 
them  suffices ;  and  the  same  kind  of  combination  is  then  formed,  as 
exists  in  the  single  article  of  bread.  Those  in  whose  diet  the  farina- 
ceous elements  predominate  largely,  and  the  azotized  compounds 
exist  in  the  smallest  amount  compatible  with  the  maintenance  of  the 
bodily  vigour,  are  exempt  from  many  diseases  incident  to  those  who 
live  more  highly ;  thus  among  the  potato-eating  Irish,  and  the  oatmeal- 
feeding  Scotch,  gout  is  a  disease  never  heard  of;  whilst  among  the 
richer  classes  of  the  same  countries,  there  is  no  peculiar  exemption 
from  it. 

435.  The  oily  constituents  of  food  are  most  abundant  in  the  diet 
of  the  inhabitants  of  frigid  zones,  who  feed  upon  whales,  seals,  and 
other  animals  loaded  with  fat,  and  who  devour  this  fat  with  avidity, 
as  if  instinctively  guided  to  its  use.  It  is  by  the  enormous  quantity 
of  this  substance  taken  in  by  them,  that  they  are  enabled  to  pass  a 
large  part  of  the  year  in  a  temperature  below  that  of  our  coldest  win- 
ter, spending  a  great  portion  of  their  time  in  the  open  air  ;  as  well  as 
to  sustain  the  extreme  of  cold,  to  which  they  are  occasionally  sub- 
jected. And  in  consequence  of  its  being  more  slowly  introduced 
into  the  system  than  most  other  substances,  a  larger  quantity  may  be 
taken  in  at  one  time,  without  palling  the  appetite  ;  whilst  its  bland 
and  non-irritating  character  favours  its  being  retained  until  it  is  all 
absorbed.  In  this  manner,  the  Esquimaux  and  Greenlanders  are 
enabled  to  take  in  20  or  30  pounds  of  blubber  at  a  meal ;  and,  when 
thus  supplied,  to  pass  several  days  without  food. — On  the  other  hand, 
among  the  inhabitants  of  warm  climates  there  is  comparatively  little 
disposition  to  the  use  of  oily  matter  as  food ;  and  the  quantity  of  it 
contained  in  most  articles  of  their  diet  is  comparatively  small. 

436.  In  the  Milk,  which  is  the  sole  nutriment  of  young  Mammalia 
during  the  period  immediately  succeeding  their  birth,  we  find  an  ad- 
mixture of  albuminous,  saccharine,  and  oleaginous  substances;  w^hich 
indicates  the  intention  of  the  Creator,  that  all  these  should  be  em- 
ployed as  components  of  the  ordinary  diet.  The  Casein  or  cheesy 
matter  is  a  proteine-compound ;  the  Butyrine  of  butter  is  but  a  slight 
modification  of  its  ordinary  fats;  and  its  sugar  differs  from  that  in 
common  use,  only  by  its  larger  proportion  of  water.  The  relative 
amount  of  these  ingredients  in  the  milk  of  different  animals  is  subject, 
as  we  shall  hereafter  see,  to  considerable  variation ;  but  they  con- 
stantly exist,  at  least  in  the  milk  of  the  Herbivorous  Mammalia,  and 
of  those  which,  like  Man,  subsist  upon  a  mixed  diet.  But  it  has  been 
recently  asserted,  that  the  milk  of  the  purely  Carnivorous  animals  is 

17 


258  IMPORTANCE  OF  VARIETY  IN  MATERIALS  OF  FOOD. 

destitute  of  Sugar,  consisting,  like  their  food,  of  proteine-compounds 
and  fatty  matter  only. 

437.  No  fact  in  Dietetics  is  better  established  than  the  impossibi- 
lity of  long  sustaining  health,  or  even  life,  upon  any  single  alimentary 
principle.  Neither  pure  albumen  nor  fibrin,  gelatin  nor  gum,  sugar  nor 
starch,  oil  nor  fat,  taken  alone  for  any  length  of  time,  can  serve  for  the 
due  nutrition  of  the  body.  This  is  partly  due,  so  far  as  the  non- 
azotized  compounds  are  concerned,  to  their  incapability  of  supplying 
the  waste  of  the  albuminous  tissues.  This  reason  does  not  apply, 
however,  to  the  proteine-compounds;  which  can  serve  not  only  for  the 
reparation  of  the  body,  but  can  also  afford  .the  carbon  and  hydrogen 
requisite  for  the  sustenance  of  its  temperature.  The  real  cause  is  to 
be  found  in  the  fact,  that  the  continued  use  of  single  alimentary  sub- 
stances excites  such  a  feeling  of  disgust,  that  the  animals  experi- 
mented on  seem  at  last  to  prefer  starvation,  rather  than  the  ingestion 
of  them.  Consequently  it  is  quite  impossible  to  ascertain,  by  such 
experiments,  the  nutritive  power  of  the  different  alimentary  princi- 
ples ;  no  animal  being  capable  of  sustaining  life  upon  less  than  two 
of  them  at  least.  The  same  disgust  is  experienced  by  Man,  when 
too  long  confined  to  any  article  of  diet,  which  is  very  simple  in  its 
composition  ;  and  a  craving  for  change  is  then  experienced,  which 
the  strongest  will  is  scarcely  able  to  resist.  Thus,  in  the  treatment 
of  Diabetes,  a  disease  in  which  there  is  an  undue  tendency  to  the 
production  of  sugar  in  the  system,  it  is  very  important  to  abstain 
completely  from  the  introduction  of  saccharine  or  farinaceous  matters 
in  the  food ;  but  the  craving  for  vegetable  food,  which  is  experienced 
when  the  diet  has  long  consisted  of  meat  alone,  is  such  as  to  make 
perseverance  in  the  latter  very  diflficult;  and  a  means  has  been  latterly 
devised  of  supplying  this  want  without  injury,  by  the  use  of  bread 
from  which  the  starchy  portion  has  been  removed,  the  gluten  or  azo- 
tized  matter  alone  being  eaten.* 

438.  The  organic  compounds,  which  have  been  enumerated  as 
supplying  the  various  wants  of  the  system,  would  be  totally  useless 
without  the  admixture  of  certain  inorganic  substances,  which  also 
form  a  constituent  part  of  the  bodily  frame,  and  which  are  constantly 
being  voided  by  the  excretions,  especially  in  the  Urine.  These  sub- 
stances have  various  uses  in  the  system.  Thus  common  Salt,  or  the 
Chloride  of  Sodium,  appears  to  afford,  by  its  decomposition,  the  mu- 
riatic acid  which  is  concerned  in  the  digestive  process,  and  the  soda 

•  As  an  illustration  of  the  advantage  of  this  treatment,  even  in  unpromising  cases, 
the  Author  may  cite  an  instance  which  has  come  under  his  own  observation.  The 
patient  was  a  man  72  years  of  age ;  the  disease  had  lasted  at  least  a  year,  and  was 
decidedly  on  the  increase ;  considerable  loss  of  flesh  and  of  muscular  vigour  had  taken 
place;  and  the  quantity  of  sugar  in  the  urine  was  such  as  to  make  it  quite  sweet  to 
the  taste.  By  the  careful  restriction  of  his  diet  to  animal  flesh  and  gluten-bread,  this 
individual  has  kept  the  disease  in  complete  check  for  more  than  15  months ;  he  has 
gained  flesh,  and  improved  in  strength;  and  his  urine  is  no  longer  sweet.  Having 
two  or  three  times  ventured  upon  a  return  to  his  ordinary  diet,  his  old  symptoms  have 
immediately  manifested  themselves,  warning  him  of  the  necessity  of  perseverance  in 
the  strict  regimen  prescribed  for  him. 


NECESSARY  MATERIALS  OF  ANIMAL  FOOD.  259 

which  is  an  important  constituent  of  the  bile.  Its  presence  in  the 
serura  of  the  blood,  also,  and  in  the  various  animal  fluids  which  are 
derived  from  this,  probably  aids  in  preventing  the  decomposition  of 
the  organic  constituents  of  these  fluids, — Phosphorus  has  been  sup- 
posed, until  recently,  to  be  chiefly  requisite  as  one  of  the  materials  of 
the  nervous  tissue  (§  383) ;  and  also,  when  acidified  by  oxygen,  to 
unite  with  lime  in  forming  the  bone-earth  by  which  bone  is  consoli- 
dated. But  there  is  reason  to  believe,  from  the  results  of  late  inqui- 
ries, that  the  acid  and  alkaline  phosphate  of  lime  and  soda  are  very 
important  constituents  of  the  various  fluid  secretions,  and  have  a  large 
share  in  their  respective  actions.  It  has  even  been  maintained  that 
the  acid  phosphate  of  lime  is  the  essential  ingredient  in  the  gastric  juice, 
by  which  the  first  solutions  of  the  food  are  effected. — Sulphur  exists  in 
small  quantities  in  several  animal  tissues;  but  its  part  appears  to  be 
by  no  means  so  important  as  that  performed  by  Phosphorus. — Lime  is 
required  for  the  consolidation  of  the  bones,  and  for  the  production  of 
the  shells  and  other  hard  parts  that  form  the  skeletons  of  the  Inverte- 
brata  ;  and  also  as  the  base  of  the  acid  phosphate,  which  has  been 
just  referred  to  as  an  important  constituent  of  the  animal  fluids. — 
Lastly,  Iron  is  an  essential  constituent  of  Hsematosine ;  and  is  conse- 
quently required  for  the  production  of  the  red  corpuscles  of  the  blood 
in  Vertebrated  animals. 

439.  These  substances  are  contained,  more  or  less  abundantly,  in 
most  of  the  articles  generally  used  as  food  ;  and  where  they  are  defi- 
cient, the  animal  suffers  in  consequence,  if  they  be  not  supplied  in  any 
other  way. — Thus,  common  Salt  exists,  in  no  inconsiderable  amount, 
in  the  flesh  and  fluids  of  animals,  in  the  milk,  and  in  the  substance  of 
the  egg;  it  is  not  so  abundant,  however,  in  Plants  ;  and  the  deficiency 
is  usually  supplied  to  herbivorous  animals  in  some  other  way.  Thus, 
salt  is  purposely  mingled  with  the  food  of  domesticated  animals  ;  and 
in  most  parts  of  the  world  inhabited  by  wild  cattle,  there  are  spots 
where  it  exists  in  the  soil,  and  to  which  they  resort  to  obtain  it.  Such 
are  the  *'  bufifalo-licks"  of  North  America. — Phosphorus  exists  also,  in 
combination  with  proteine-compounds,  in  all  animal  substances  com- 
posed of  these  ;  and  in  the  state  of  phosphate,  combined  with  lime, 
magnesia,  and  soda,  it  exists  largely  in  many  vegetable  substances  ordi- 
narily used  as  food.  The  phosphate  of  lime  is  particularly  abundant 
in  the  seeds  of  the  grasses  ;  and  it  also  exists  largely,  in  combination 
with  casein,  in  Milk. — Sulphur  is  also  derived  alike  from  vegetable 
and  animal  substances.  It  exists,  in  union  with  proteine-compounds, 
in  flesh,  eggs,  and  milk  ;  also  in  several  vegetable  substances ;  and, 
in  the  form  of  sulphate  of  lime,  in  most  of  the  river  and  spring  water 
that  we  drink. 

440.  Lime  is  one  of  the  most  universally  diffused  of  all  mineral 
bodies;  for  there  are  very  few  Animal  or  Vegetable  substances  in  which 
it  does  not  exist.  The  principal  forms  in  which  it  is  an  element  of 
Animal  nutrition,  are  the  carbonate  and  phosphate.  Both  these  are 
found  in  the  ashes  of  the  grasses,  and  of  other  plants  used  as  food ; 


260  MINERAL  SUBSTANCES  REQUIRED  BY  ANIMALS. 

the  phosphate  of  lime  being  particularly  abundant  (as  already  men- 
tioned) in  the  corn-grains.  The  production  of  these  cannot  take 
place,  to  their  fullest  extent,  unless  the  soil  previously  contain  phos- 
phate of  lime  in  a  state  in  which  the  plant  can  receive  it ;  and  it  is 
now  understood,  that  the  diminished  fertility  of  many  lands  is  due, 
in  great  part,  to  the  exhaustion  of  the  soil  as  regards  this  ingredient. 
The  restoration  of  the  alkaline  and  earthy  phosphates  to  the  soil,  in 
the  form  of  manure,  is  the  obvious  means  of  preserving  its  fertility  ; 
but  so  long  as  a  very  large  proportion  of  the  excrements  of  animals 
(the  materials  of  which  are  originally  derived  from  the  earth,  through 
the  vegetables  it  supplies),  is  allowed  to  run  to  waste,  so  long  will  it 
be  necessary  that  the  requisite  amount  of  phosphate  of  lime  should 
be  drawn  from  foreign  sources. 

441.  The  phosphate  of  lime,  as  already  mentioned,  seems  to  per- 
form important  offices  of  a  chemical  nature  in  the  animal  economy, 
besides  being  the  chief  solidifying  ingredient  of  bones  and  teeth  ;  but 
the  carbonate  would  seem  principally  destined  to  mechanical  uses 
only;  and  we  find  it  predominating,  or  existing  as  the  sole  mineral 
ingredient,  in  those  non-vascular  tissues  of  the  Invertebrated  animals, 
which  give  support  and  protection  to  their  soft  parts  (§  289).  The 
degree  of  development  of  these  tissues  depends  in  great  part  upon  the 
supply  of  carbonate  of  lime  which  the  animals  receive.  Thus,  the 
Mollusca  which  inhabit  the  sea,  find  in  its  waters  the  proportion  of 
that  substance  which  they  require ;  but  those  which  dwell  in  streams 
and  fresh  water  lakes,  that  contain  but  a  small  quantity  of  lime,  form 
very  thin  shells  ;  whilst  the  very  same  species  inhabiting  lakes,  which, 
from  peculiar  local  causes,  contain  a  large  impregnation  of  calcareous 
wiatter,  form  shells  of  remarkable  thickness. — The  Crustacea,  which 
periodically  throw  off  their  calcareous  envelop  (§  297),  are  enabled 
to  renew  it  with  rapidity  by  a  very  curious  provision.  There  is  laid 
up  in  the  walls  of  their  stomachs  a  considerable  supply  of  calcareous 
matter,  in  the  form  of  little  concretions,  which  are  commonly  known 
as  *'  crabs'  eyes."  When  the  shell  is  thrown  off,  this  matter  is  taken 
up  by  the  circulating  current,  and  is  thrown  out  from  the  surface, 
mingled  with  the  animal  matter  of  which  the  shell  is  composed.  This 
hardens  in  a  day  or  two,  and  the  new  covering  is  complete.  The 
concretions  in  the  stomach  are  then  found  to  have  disappeared  ;  but 
they  are  gradually  replaced,  before  the  supply  of  lime  they  contain  is 
again  drawn  upon.  The  large  amount  of  carbonate  of  lime  which  is 
required  by  the  laying  Hen,  is  derived  from  chalk,  mortar,  or  other 
substances  containing  it,  which  she  is  compelled  by  her  instinct  to 
eat;  and  if  the  supply  of  these  be  withheld,  the  eggs  which  she 
deposits  are  soft  on  their  exterior, — not  being  destitute  of  shell,  as 
commonly  supposed, — but  having  the  fibrous  element  of  the  shell 
(§  181)  unconsolidated  by  the  intervening  deposit  of  chalky  particles. 


SIMPLEST  FORMS  OF  DIGESTIVE  APPARATUS.  261 

2.   Of  the  Digestive  Apparatus,  and  its  Actions  in  general. 

442.  It  has  been  already  pointed  out,  that  the  nature  of  the  food 
of  Animals  is  so  far  different  from  that  of  Plants,  as  to  require  the 
preparatory  process  of  Digestion,  before  its  nutritious  parts  can  be 
taken  up  by  the  absorbent  vessels  and  received  into  the  system. 
This  process  may  be  said  to  have  three  different  purposes  in  view : — 
the  reduction  of  the  alimentary  matter  to  a  fluid  form,  so  that  it 
may  become  capable  of  absorption ;  the  separation  of  that  portion  of 
it  which  is  fit  to  be  assimilated  or  converted  into  organized  texture, 
from  that  which  cannot  serve  this  purpose,  and  w^hich  is  at  once 
rejected; — and  the  alteration,  to  a  certain  extent  when  required,  of 
the  chemical  constitution  of  the  former,  which  prepares  it  for  the 
important  changes  it  is  subsequently  to  undergo.  The  simplest  con- 
ditions requisite  for  the  accomplishment  of  these  purposes  are  the 
following: — a  fluid  capable  of  performing  the  solution,  and  of  effect- 
ing the  required  chemical  changes; — a  fluid  capable  of  separating 
the  excrementitious  matter,  by  a  process  analogous  to  chemical  pre- 
cipitation ; — and  a  cavity  or  sac  in  which  these  operations  may  be 
performed. 

443.  In  the  lowest  Animals,  we  find  this  cavity  formed  upon  a 
very  simple  plan;  the  digestive  sac  being  a  mere  excavation  in  the 
solid  tissue  of  the  body,  lined  with  a  membrane  which  is  an  inverted 
continuation  of  the  external  integument,  and  communicating  with  the 
exterior  by  one  orifice  only,  through  which  food  is  drawn  in,  and 
excrementitious  matter  rejected.  In  the  little  Hydra,  or  fresh-water 
Polype,  the  external  covering  of  the  body  and  the  lining  of  the 
stomach  correspond  so  closely  in  their  structure, — their  actions  dif- 
fering only  with  their  situation, — as  to  be  mutually  convertible ;  for 
the  animal  may  be  turned  completely  inside-out,  without  its  functions 
being  deranged.  The  fluid  necessary  to  dissolve  the  food,  known  by 
the  name  of  *' gastric  fluid,"  or  **  gastric  juice,"  is  secreted  in  the 
walls  of  the  stomach;  and,  from  the  transparency  of  the  tissues,  the 
whole  process  may  be  watched.  The  prey  is  frequently,  and  indeed 
generally  introduced  alive,  by  the  contractile  powder  of  the  arms, 
which  coil  round  it,  and  gradually  draw  it  into  the  mouth  or  entrance 
to  the  stomach ;  and  its  movements  may  often  be  observed  to  con- 
tinue for  some  time  after  it  has  been  swallow^ed.  In  a  little  time, 
however,  its  outline  appears  less  distinct,  and  a  turbid  film  partly 
conceals  it;  the  soft  parts  are  soon  dissolved  and  reduced  to  a  fluid 
state ;  and  any  firm  indigestible  portions  which  the  body  may  con- 
tain, are  rejected  through  the  aperture  by  which  it  entered.  The 
nutritive  matter  is  absorbed  by  the  walls  of  the  stomach,  every  part 
of  which  appears  to  be  endowed  with  equal  power  in  this  respect ; 
and  it  is  conveyed  to  the  remoter  parts  of  the  arms  by  the  simple 
imbibition  of  one  part  from  another,  without  any  proper  circulation 
through  vessels. 

444.  In  Polypes  of  a  higher  conformation,  however,  the  digestive 
cavity  is  provided  with  a  second  orifice ;  from  the  dilated  cavity  or 


262  VARIOUS  FORMS  OF  DIGESTIVE  APPARATUS. 

stomach,  an  intestinal  tube  proceeds  ;  and  this  has  a  termination  dis- 
tinct from  the  mouth,  though  often  in  its  neighbourhood.  The  food, 
before  entering  the  stomach,  is  submitted  to  a  powerful  triturating 
apparatus,  resembling  the  gizzard  of  birds,  by  which  it  is  broken 
down ;  and  in  the  digestive  cavity  it  is  submitted,  not  merely  to  the 
action  of  the  gastric  fluid,  but  also  to  that  of  the  bile,  which  is 
secreted  in  little  follicles  in  the  walls  of  the  stomach,  and  which  is 
poured  into  its  cavity  during  the  process  of  digestion, — being  easily 
recognized  by  its  bright  yellow  colour.  The  excrementitious  matter 
is  rejected  in  the  form  of  little  pellets,  through  the  intestinal  tube. 

445.  As  we  ascend  the  Animal  scale,  we  find  the  digestive  appa- 
ratus gradually  increased  in  complexity  ;  but  its  essential  characters 
remain  the  same.  Near  the  entrance  to  the  stomach,  we  usually  find 
an  apparatus  for  effecting  the  mechanical  reduction  of  the  food,  by 
which  its  subsequent  solution  may  be  rendered  more  easy.  This  may 
consist  of  a  set  of  teeth  ;  either  fixed  in  the  mouth,  as  in  Mammalia 
and  Reptiles ;  or  more  particularly  besetting  the  pharynx,  as  in 
Fishes;  or  attached  to  the  walls  of  the  stomach,  as  in  Crustacea. 
Or  it  may  be  formed  by  the  tongue,  converted  into  a  sort  of  rasp ;  as 
in  the  common  Limpet,  which  thus  reduces  the  sea-weeds  that  con- 
stitute its  chief  food.  Or  the  same  purpose  may  be  answered  by  a 
gizzard,  or  first  stomach,  with  dense  muscular  and  tendinous  walls; 
such  as  we  find  in  the  grain-eating  Birds,  and  many  Insects,  and  in 
certain  Mollusks  and  Polypes.  But  where  the  food  is  already  com- 
posed of  very  minute  particles,  or  is  received  in  a  liquid  state,  (as  in 
the  case  of  those  animals  which  live  upon  the  juices  of  others,)  or  is 
easily  acted  on  by  the  gastric  juice,  no  such  preparation  is  requisite. 

446.  Before  the  food  reaches  the  true  digestive  stomach,  it  is 
sometimes  delayed  in  a  previous  cavity,  in  order  that  it  may  be 
macerated  in  fluid,  and  may  be  thoroughly  saturated  with  it.  This 
is  the  purpose  of  the  crop  of  Birds,  and  of  the  first  stomach  of  Ru- 
minant animals.  When  this  incorporation  with  fluid  is  not  effected 
before  the  food  is  subjected  to  the  triturating  process,  it  usually  takes 
place  concurrently  with  it ;  and  in  those  animals  which  reduce  their 
food  in  the  mouth  by  the  process  of  mastication,  there  is  a  special 
secretion  of  fluid  into  that  cavity  for  this  purpose  ;  this  fluid  is  termed 
Saliva,  and  the  act  by  which  it  is  incorporated  with  the  food  is  termed 
insalivation.  The  mechanical  reduction  of  the  aliment,  and  its  in- 
corporation with  fluid,  constitute,  as  we  shall  hereafter  see,  a  very 
important  preparation  for  the  true  digestive  process. 

447.  This  process,  among  higher  animals,  takes  place  exclusively, 
or  nearly  so,  in  the  stomach;  the  form  of  which  varies  with  the  cha- 
racter of  the  food.  When  this  is  of  a  nature  to  be  easily  acted  on  by 
the  gastric  fluid,  the  stomach  is  a  simple  enlargement  of  the  aliment- 
ary canal,  almost  in  the  direct  line  between  the  oesophagus  and  the 
intestinal  tube ;  so  that  there  is  little  provision  for  the  delay  of  the 
food  in  its  cavity.  But  when  the  aliment  is  such  as  to  be  less  easily 
reduced,  and  requires  to  be  submitted  to  the  action  of  the  gastric 
fluid,  for  a  longer  period,  the  stomach  forms  a  more  considerable 


VARIOUS  FORMS  OF  DIGESTIVE  APPARATUS. 


263 


enlargement,  and  is  placed  more  out  of  the  direct  line  between  the 
oesophagus  and  the  commencement  of  the  intestine.  The  former 
condition  obtains  in  the  Carnivora,  and  particularly  in  those  which 
live  more  upon  blood  than  upon  flesh, — such  as  Weasels,  Stoats,  &c., 
in  which  this  part  of  the  alimentary  tube  is  almost  straight ;  the  latter 
condition  is  found  among  the  Herbivora,  and  the  provision  for  the 
delay  of  the  aliment  attains  its  greatest  complexity  in  the  Ruminant 
animals.  The  form  of  the 

Human  stomach  (Fig.  70)  Fig.  70. 

is  intermediate  between 
that  of  purely  carnivo- 
rous and  purely  herbivo- 
rous animals.  As  in  the 
former,  there  is  a  direct 
passage  from  the  cardiac 
orifice  or  entrance  of  the 
oesophagus,  to  the  pyloric 
orifice  or  commencement 
of  the  intestine ;  but  there 
is  also  a  considerable  di- 
latation or  cul  de  sac, 
which  is  out  of  that  line ; 
and  it  appears  that, 
during  the  digestive  pro- 
cess, there  is  a  constric- 
tion across  the  stomach, 
which  separates  the  car- 
diac portion  from  the  py- 
loric, and  causes  the  re- 
tention of  the  food  in  the 
dilated  part  or  large  ex- 
tremity. The  gastric  fluid 
is  still  secreted  in  the 
walls  of  this  organ,  by 
scattered  follicles  which 
pour  their  products  into 
its  cavity  through  sepa- 
rate orifices;  but  the  bile  is  elaborated  by  a  distinct  organ,  alto- 
gether removed  from  it,  which  transmits  its  secretion  by  a  single 
duct,  that  opens  into  the  intestinal  tube  at  a  short  distance  from  its 
commencement. 

448.  The  action  of  the  Stomach  is  restricted,  in  the  higher  animals, 
to  the  reduction  of  the  food  by  the  solvent  powers  of  the  gastric  juice, 
and  to  the  absorption  (by  the  vessels  in  its  walls)  of  those  parts  of  it 
which  are  in  a  state  of  the  most  perfect  solution.  The  change  which 
is  produced  by  the  admixture  of  the  bile,  takes  place  in  the  intestine ; 
and  the  principal  part  of  the  nutritive  elements  of  the  food  are  taken 
up  by  the  absorbent  vessels  of  the  walls  of  the  intestine,  after  that 
process  has  been  accomplished.     It  would  seem  as  if  the  preparation 


A  vertical  and  longitudinal  section  of  the  Human  stomach 
and  duodenum,  made  in  such  a  direction  as  to  include  the 
two  orifices  of  the  stomach,  1.  The  oesophagus;  upon  its 
internal  surface  the  plicated  arrangement  of  the  cuiicular 
epithelium  is  shown.  2.  The  cardiac  orifice  of  the  stomach, 
around  which  the  fringed  border  of  the  cuticular  epithelium 
is  seen.  3.  The  great  end  of  the  stomach.  4.  Its  lesser  or 
pyloric  end.     5.  The  lesser  curve.     6.  The  greater  curve. 

7.  The  dilatation  at  the  lesser  end  of  the  stomach,  which  has 
received  from  Willis  the  name  of  antrum  of  the  pylorus. 
This  may  be  regarded  as  the  rudiment  of  a  second  stomach. 

8.  The  rugae  of  the  stomach  formed  by  the  mucous  mem- 
brane :  their  longitudinal  direction  is  shown.  9.  The  pylo- 
rus.   10.  The  oblique  portion  of  the  duodenum.     11.  The 


descending  portion.  12.  The  pancreatic  duct  and  the  ductus 
communis  choledochus  close  to  their  termination.  13.  The 
papilla  upon  which  the  ducts  open.  14.  The  transverse 
portion  of  the  duodenum.  15.  The  commencement  of  the 
jejunum.  In  the  interior  of  the  duodenum  and  jejunum,  the 
valvulee  conniventes  are  seen. 


264  DIGESTIVE  APPARATUS  OF  MAN. 

of  the  food  for  absorption  were  not  by  any  means  completed,  in  this 
first  portion  of  the  alimentary  canal ;  for  it  is  still  destined  to  pass 
through  a  long  and  convoluted  tube,  which  is  sometimes  extended 
to  an  extraordinary  degree ;  and  in  this  passage  it  is  gradually  ex- 
hausted of  its  nutritious  matter.  The  length  of  the  intestinal  canal 
bears  a  close  relation  to  the  character  of  the  food.  In  the  Carnivorous 
animals,  whose  aliment  is  easily  dissolved  and  prepared  for  conver- 
sion into  blood,  the  intestine  is  comparatively  short;  thus  in  the  Lion 
and  other  Felines  it  is  no  more  than  three  times  the  length  of  the 
body ;  and  in  some  of  the  blood-sucking  Bats,'it  is  almost  straight  and 
simple.  On  the  other  hand,  in  Herbivorous  animals  it  is  of  enor- 
mous length ;  thus  in  the  Sheep  it  is  about  twenty-eight  times  as  long 
as  the  body.  In  animals  whose  diet  is  mixed,  its  length  is  inter- 
mediate between  these  extremes ;  thus  in  Man,  the  whole  length  of 
the  intestinal  tube  is  about  thirty  feet,  or  between  five  and  six  times 
that  of  the  body. — The  intestine  is  of  much  smaller  diameter  along  its 
first  portion,  than  it  is  nearer  its  termination ;  and  it  is  consequently 
distinguished  into  the  small  and  the  large.  In  the  small  intestine, 
which  constitutes  in  Man  about  five-sixths  of  the  whole,  the  surface 
of  the  mucous  membrane  is  greatly  extended  by  the  valvulce  conni- 
ventes,  which  are  folds  or  duplicatures,  often  several  lines  in  breadth, 
not  entirely  surrounding  the  intestine,  but  extending  for  about  one- 
half,  or  three-fourths  of  its  circumference.  These  are  wanting  at  the 
lower  part  of  the  ileum.  The  whole  surface  of  the  mucous  membrane 
of  the  small  intestine,  below  the  entrance  of  the  biliary  ducts,  is  thickly 
covered  with  villi,  or  little  root-like  projections,  in  which  the  proper 
absorbent  vessels  originate.  No  proper  valvulae  conniventes  exist  in 
the  large  intestine ;  the  only  extensions  of  the  raucous  membrane 
being  crescentic  folds  at  the  edges  of  the  sacculi  or  pouch-like  dila- 
tations in  its  walls ;  and  the  villi  are  comparatively  few  in  number, 
gradually  disappearing  towards  the  termination  of  the  intestine. 

449.  The  mucous  membrane  of  the  alimentary  canal,  through  its 
whole  course,  is  studded  with  the  orifices  of  numerous  scattered 
glands,  which  lie  in  its  thickness,  or  immediately  beneath  it.  The 
simplest  of  these  are  the  follicles  of  Lieberkiihn,  which  are  small 
pouches,  formed  by  an  inflexion  of  the  mucous  surface,  analogous  to 
the  follicles  of  other  mucous  membranes,  and 
Fig.  71.  apparently  destined  for  the  elaboration  of  the 

protective  secretion  (§  237,  see  Figs.  27  and 
28).     These  follicles,  in  the  small  intestine,  are 
very  simple  in  their  character,  and   not   very 
deep ;  and  their  apertures,  which  are  small,  are 
situated  for  the  most  part  around  the  bases  of  the 
villi.     In  the  large  intestine  they  are  more  pro- 
Mucous  coat  of  smaii  in-    longed,  especially  towards  the  extremity  of  the 
the 'fbuicies  of  Lieberkiihn    icctum,  whcrc  they  form   a  distinct  layer,  the 
f^cviiTon^  ''"^''°"'  ^^''^    component   tubes   of  which  are  visible  to  the 
naked  eye ;  they  probably  form  the   peculiarly 
thick   and  tenacious  mucus  of  that  part.     These  mucous  follicles 


ALIMENTARY  CANAL  AND  ITS  MOVEMENTS.  265 

become  particularly  evident  when  the  membrane  is  inflamed ;  for  they 
then  secrete  an  opaque  whitish  matter,  which  is  absent  in  the  healthy 
state,  and  which  distinguishes  their  orifices  (Fig.  71). — A  modified 
kind  of  these  follicles,  rather  more  complex  in  structure,  is  found 
abundantly  in  the  stomach;  where  it  is  concerned  in  the  secretion  of 
the  gastric  fluid  (§  469). 

450.  The  coats  of  the  intestine  contain  other  glandulse,  which 
appear  destined,  not  so  much  to  elaborate  fluids  of  use  in  the  system, 
as  to  draw  off*  from  the  blood  certain  products  of  decomposition, 
which  are  to  be  excreted  from  it.  These  are  commonly  known  as 
the  glands  of  Brunner,  and  of  Peyer,  after  the  names  of  their  respective 
discoverers. — The  glands  of  Brunner  are  situated  in  the  duodenum, 
and  lie,  not  in  the  mucous  but  in  the  sub-mucous  tissue.  Though 
their  size  is  only  about  that  of  a  hemp-seed,  they  are  of  very  complex 
structure,  consisting  of  several  hundred  follicles,  clustered  round  the 
ramifications  of  an  excretory  duct,  so  as  to  resemble  the  Salivary 
glands ;  and  each  pours  its  secretion  through  a  single  orifice  into  the 
intestinal  tube.  The  glands  of  Peyer  are  either  solitary  ot  agminated; 
the  latter  form  large  patches,  which  are  made  up  of  aggregations  of 
the  former.  Each  solitary  gland  consists  of  a  closed  spheroidal  vesi- 
cle, which  is  half  imbedded  in  the  mucous  membrane,  but  which 
also  forms  an  elevated  projection  above  it;  and  this  projection  is  sur- 
rounded by  a  ring  or  zone  of  openings,  which  lead  into  an  annular 
cluster  of  Lieberkiihnian  follicles.  On  rupturing  one  of  the  Peyerian 
vesicles,  its  cavity  is  found  to  contain  a  grayish-white  matter,  inter- 
spersed with  cells  in  various  stages  of  development.  The  complete 
closure  of  this  cavity  would  seem  to  render  it  an  exception  to  all 
general  rules  of  glandular  structure  ;  but  this  is  not  so  in  reality  ;  for 
it  will  be  shown  hereafter  that  many  other  glandular  follicles  in  an 
early  stage  of  their  development  are  equally  closed  (Chap.  IX.);  and 
it  appears  that  the  Peyerian  vesicles,  when  mature,  discharge  their 
contents  by  an  opening  which  then  forms  in  the  most  projecting  por- 
tion of  their  walls, — these  contents  passing  at  once  into  the  cavity  of 
the  intestine,  instead  of  being  poured  (as  in  other  cases)  into  an 
excretory  duct. — Of  the  nature  of  the  secretions  of  these  intestinal 
glandulse,  nothing  has  been  positively  ascertained  ;  but  some  probable 
inferences  from  well-known  facts  will  be  stated  hereafter  (Chap.  XI). 

3.  Movements  of  the  Alimentary  Canal, 

451.  The  food  which  is  conveyed  to  the  mouth,  is  grasped  with 
the  lips,  by  a  muscular  eflfort,  which  is  voluntary  in  the  adult  under 
ordinary  circumstances,  but  which  may  be  performed  instinctively 
when  the  influence  of  the  will  is  withdrawn ;  in  the  infant,  as  among 
the  lower  animals,  the  action  seems  purely  instinctive,  the  nipple  of 
the  mother  being  firmly  grasped  by  the  lips  when  introduced  between 
them,  even  after  the  brain  has  been  removed. — By  the  act  of  masti- 
cation, which  then  succeeds,  the  food  is  triturated  and  mingled  with 


266  MASTICATION. 

the  salivary  secretion  ;  and  is  thus  prepared  for  the  further  process  of 
solution,  to  which  it  is  to  be  subjected  in  the  stomach.  The  degree 
of  this  preparation,  and  the  form  of  the  instruments  by  which  it  is 
effected,  vary  in  different  animals,  according  to  the  nature  of  the  food. 
In  those  Carnivora,  whose  aliment  consists  exclusively  of  flesh,  very 
litde  mastication  is  necessary,  because  this  substance  is  very  readily 
acted  on  by  the  gastric  fluid ;  and  we  accordingly  find  the  molar  teeth 
raised  into  sharp  cutting  edges,  and  working  against  each  other  with 
a  scissors-like  action  (the  only  one  permitted  by  the  articulation  of  the 
jaw),  so  as  simply  to  divide  the  food.  On  the  other  hand,  in  those 
Herbivora,  whose  food  consists  of  tough  vegetable  substances,  such 
as  the  leaves  of  grasses,  or  the  stems  and  roots  of  other  plants,  we 
find  the  molar  or  grinding  teeth  peculiarly  adapted  to  its  reduction ; 
their  surface  being  extended  horizontally,  and  being  kept  continually 
rough,  by  the  alternation  of  vertical  plates  of  different  degrees  of 
hardness;  and  the  lower  jaw  being  so  connected  with  the  skull,  that 
great  freedom  of  motion  is  permitted.  In  Man  we  find  an  inter- 
mediate conformation,  as  regards  both  the  teeth  and  the  articulation 
of  the  jaw;  for  the  molar  teeth  possess  broad  surfaces,  which  are 
covered  with  a  continuous  coat  of  enamel,  but  which  are  raised  into 
rounded  tubercles;  and  the  articulation  of  the  jaw  allows  it  a  degree 
of  freedom,  which  is  much  greater  than  that  possessed  by  the  Carni- 
vora ;  although  inferior  to  that  which  exist  in  many  Herbivora.  The 
whole  apparatus  of  Mastication  is  so  formed  in  Man,  as  to  lead  to  the 
conclusion  that  he  is  destined  to  live  on  a  mixed  diet,  composed  in 
part  of  animal  flesh,  and  in  part  of  vegetable  substances  that  are 
sufficiently  soft  to  be  reduced  by  the  simple  act  of  crushing,  or  by  the 
slight  trituration  for  which  the  molar  teeth  are  adapted. 

452.  The  mechanical  reduction  of  the  food  by  Mastication,  and 
the  incorporation  of  the  Salivary  secretion  with  its  substance,  consti- 
tute a  very  important  step  in  the  Digestive  process.  We  shall  here- 
after see  that  the  operations,  to  which  the  alimentary  matter  is 
subjected  in  the  stomach,  are  of  a  purely  Chemical  nature  ;  and  this 
preparation  is  exactly  of  the  same  character  as  that  which  the  Chemist 
finds  it  advantageous  to  make,  when  he  is  operating  on  a  substance 
of  difficult  solution.  For  nothing  is  so  favourable  to  the  action  of 
the  solvent,  as  the  previous  reduction  of  the  matter  to  be  dissolved, 
and  its  thorough  incorporation  with  the  fluid  that  is  to  act  upon  it. 
We  shall  hereafter  see,  that  the  relative  properties  of  the  Saliva  and 
of  the  Gastric  fluid  are  such,  that,  by  the  minute  admixture  of  the 
food  with  the  former,  the  latter  finds  access  to  every  particle  of  it. 
Hence  the  practice  of  eating  so  rapidly,  that  Mastication  and  Insali- 
vation  are  insuflSciently  performed,  is  extremely  injurious;  since  it 
throws  more  work  upon  the  Stomach  than  it  ought  to  perform,  by 
rendering  its  solvent  action  more  difficult.  There  can  be  no  doubt 
that,  by  the  prolonged  continuance  of  it,  a  foundation  is  laid  for  the 
distressing  complaint  termed  Dyspepsia,  or  difficulty  of  digestion  ;  and 
where  any  form  of  this  complaint  exists,  too  much  attention  cannot 
be  paid  to  the  efficient  reduction  of  the  food  in  the  mouth. 


ACT  OF  DEGLUTITION.  267 

453.  When  the  aliment  has  been  sufficiently  triturated,  it  is  con- 
veyed into  the  Pharynx  by  the  act  of  Deglutition  or  swallowing.  This 
act  involves  a  great  many  distinct  movements,  into  a  minute  descrip- 
tion of  which  we  shall  not  here  enter ;  but  it  is  desirable  that  its 
general  nature  should  be  well  understood.  It  is  one  of  those  most 
purely  reflex  in  its  character  (§  394),  and  is  not  capable  of  being  per- 
formed or  even  controlled  by  a  voluntary  effort.  This  statement  may 
seem  inconsistent  with  the  fact,  that  we  swallow  when  we  will ;  but 
it  is  not  so  in  reality.  The  muscular  movements  which  are  concerned 
in  deglutition,  are  excited  by  nerves  that  proceed  from  the  spinal  cord, 
not  from  the  brain  ;  these  motor  nerves  are  excited  to  action,  by  the 
contact  of  solid  or  fluid  matters  with  the  mucous  surface  of  the  fauces, 
— and  in  no  other  way.  The  impression  produced  by  the  contact  is 
conveyed  to  the  medulla  oblongata,  or  that  portion  of  the  spinal  cord 
which  lies  within  the  cranium,  by  afferent  nerves  that  terminate  in 
it;  and,  in  immediate  respondence  to  that  impression,  a  motor  impulse 
is  transmitted  from  it,  which  calls  the  muscles  into  the  combined  action 
necessary  to  produce  the  movement.  Now  this  contact  a/50  produces 
a  sensation,  provided  the  brain  be  sound  and  awake,  because  nervous 
fibres  proceed  from  the  mucous  surface  to  the  brain  as  w'ell  as  to  the 
spinal  cord ;  but  this  sensation  is  not  a  necessary  link  in  the  chain  of 
actions,  by  which  the  movement  is  produced  ;  for  the  act  of  Degluti- 
tion takes  place  during  profound  sleep,  when  all  sensation  is  suspended, 
and  it  may  be  excited  even  after  the  brain  has  been  removed.  It 
seems  to  be  voluntary,  under  ordinary  circumstances,  simply  because 
it  is  by  an  act  of  the  will,  that  the  matter  to  be  swallowed  is  carried 
backwards  into  contact  with  the  fauces  ;  but  that  it  is  not  so  in  reality, 
is  shown  by  the  fact,  that  when  this  impression  has  once  been  made 
with  sufficient  force,  we  cannot  by  any  effort  of  the  will,  prevent  the 
action.  We  have  a  good  example  of  this  in  the  following  circum- 
stance, of  no  very  unfrequent  occurrence.  The  tickling  of  the  upper 
part  of  the  fauces  with  a  feather  is  often  practised  to  induce  vomiting ; 
but  if  the  end  of  the  feather  be  carried  too  far  down,  it  excites  the 
act  of  deglutition  instead  ;  the  feather  is  grasped  by  the  pharynx  and 
drawn  downwards;  and  if  it  be  not  held  tenaciously  between  the 
fingers,  it  is  drawn  from  them  and  carried  dow^nwards  into  the  sto- 
mach. 

454.  The  carrying-back  of  the  alimentary  matter,  so  that  it  reaches 
the  fauces  or  upper  part  of  the  pharynx,  is  principally  accomplished 
by  the  tongue ;  when  it  has  passed  the  anterior  palatine  arches,  these 
contract  and  close  over  the  tongue,  so  as  to  prevent  the  return  of  the 
food  into  the  mouth  ;  and  at  the  same  time  the  posterior  palatine  arches 
and  the  uvula  are  so  drawn  together,  as  to  prevent  its  passage  into 
the  posterior  nares.  The  larynx  is  drawn  forwards  beneath  the  root 
of  the  tongue,  and  the  epiglottis  is  pressed  down  over  the  rima  glot- 
tidis,  so  that  nothing  can  enter  the  latter,  unless  drawn  towards  it  by 
an  act  of  inspiration.  When  fairly  within  the  pharynx,  the  alimentary 
matter  is  seized  by  the  constrictors  which  enclose  that  part  of  the  ali- 


268  MOVEMENTS  OF  (ESOPHAGUS. 

mentary  tube,  and  is  drawn  downwards  by  them  into  the  oesophagus, 
which  is  the  cylindrical  continuation  of  it.  The  continued  action  of 
the  constrictors  serves  to  propel  the  food  along  the  oesophagus ;  their 
movement  being  of  a  reflex  nature,  excited  by  the  contact  of  the  sub- 
stance contained  in  the  tube,  with  its  lining  membrane, — which  pro- 
duces an  impression  that  is  transmitted  to  the  medulla  oblongata,  and 
is  reflected  back  as  a  motor  impulse  to  the  muscles.  We  have  here 
a  distinct  case  of  reflex  action  without  sensation  ;  for  we  have  no 
consciousness  of  the  ordinary  passage  of  food  down  the  oesophagus, 
unless  it  occasion  pressure  on  the  surrounding  parts  through  its  bulk, 
or  unduly  irritate  the  lining  membrane  by  its  high  or  low  temperature 
or  its  acrid  qualities  ;  and  yet  it  may  be  shown  by  experiment,  that 
the  completeness  of  the  nervous  circle  is  requisite  for  the  excitement 
of  the  movement,  which  will  not  take  place  when  it  is  interrupted 
either  by  division  of  the  nerves,  or  by  destruction  or  paralysis  of  the 
medulla  oblongata. 

455.  The  progress  of  the  food  along  the  (Esophagus  is  aided  by 
the  action  of  the  muscular  coat  peculiar  to  it.  This  is  composed  of 
the  non-striated  fibre  ;  and,  like  that  of  the  intestinal  canal  further 
on,  it  is  usually  stimulated  to  contraction  by  the  direct  contact  of  the 
stimulus,  and  not  either  by  the  will,  or  by  the  reflex  action  of  the 
spinal  cord.  The  movement  produced  by  it  is  of  the  peristaltic  or 
wave-like  kind  ;  the  contractions  being  limited  to  one  portion  of  the 
tube,  and  being  propagated  along  it  from  above  downwards.  This 
action  continues  after  the  division  of  all  the  nerves  supplying  the 
oesophagus ;  and  it  cannot,  therefore,  be  dependent  upon  the  brain  or 
spinal  cord.  It  may  be  observed  to  take  place  in  a  rhythmical  man- 
ner (that  is,  at  short  and  tolerably  regular  intervals),  whilst  a  meal  is 
being  swallowed;  but  as  the  stomach  becomes  full,  the  intervals  are 
longer  and  the  wave-like  contractions  less  frequent.  The  degree  in 
which  the  action  of  the  oesophagus  alone,  without  that  of  the  sur- 
rounding muscles,  is  capable  of  propelling  the  food  into  the  stomach, 
seems  to  vary  in  different  animals.  When  the  latter  are  paralyzed  in 
the  Dog,  by  section  of  the  nerves  that  supply  them,  the  food  that  has 
entered  the  oesophagus  is  still  propelled  into  the  stomach ;  but  this  is 
not  the  case  in  the  Rabbit,  the  action  of  its  oesophageal  fibres  not 
being  sufficient  to  carry  the  food  onwards  to  the  stomach,  though  it 
will  expel  it  from  the  divided  extremity  of  the  tube  when  it  is  cut 
across.  The  usual  peristaltic  movements  of  the  oeosophagus  are  re- 
versed in  Vomiting;  and  this  reversion  has  been  observed,  even  after 
the  separation  of  the  stomach  from  the  oesophagus,  as  a  consequence 
of  the  injection  of  tartar  emetic  into  the  veins. 

456.  At  the  point  where  the  oesophagus  enters  the  Stomach, — the 
cardiac  orifice  of  the  latter, — there  is  a  sort  of  sphincter,  or  circular 
muscle,  which  is  usually  closed.  This  opens  when  there  is  a  suffi- 
cient pressure  on  it,  made  by  the  accumulated  food  propelled  by  the 
movements  of  the  oesophagus  above  ;  and  it  then  closes  again,  so  as 
to  retain  the  food  in  the  stomach.     The  closure  is  due  to  reflex  ac- 


TERMINATION  OF  OESOPHAGUS  IN  RUMINANTS.  269 

tion;  for  when  the  nerves  supplying  it  are  divided,  the  sphincter  no 
longer  contracts,  and  the  food  regurgitates  into  the  oesophagus.  The 
opening  of  the  cardiac  is  one  of  the  first  acts  which  takes  place  in 
vomiting. 

457.  In  Ruminating  animals,  there  is  a  very  remarkable  conforma- 
tion at  the  lower  end  of  the  oesophagus,  which  is  destined  to  regulate 
the  passage  of  food  into  the  different  compartments  of  the  stomach, 
according  as  it  has  been  submitted  to  the  second  mastication,  or  not. 
The  oesophagus  does  not  terminate  at  its  opening  into  the  first  stomach 
or  paunch,  but  it  is  continued  onwards  as  a  deep  groove  with  two  lips 
(Fig.  73) :  by  the  closure  of  these  lips  it  is  made  to  form  a  tube,  which 
serves  to  convey  the  food  onwards  into  the  third  stomach ;  but  when 
they  separate,  the  food  is  allowed  to  pass  either  into  the  first  or  the 
second  stomachs.  When  the  food  is  first  swallowed,  it  undergoes  but 
very  little  mastication ;  it  is  consequently  firm  in  its  consistence,  and 
is  brought  down  to  the  termination  of  the  oesophagus  in  dry  bulky 
masses.  These  separate  the  lips  of  the  groove  or  demi-canal,  and  pass 
into  the  first  and  second  stomachs.  After  they  have  been  macerated 
in  the  fluids  of  these  cavities,  they  are  returned  to  the  mouth  by  a 

Fig.  72. 


Stomach  of  Sheep ;— a,  cEsophagus ;  b,  paunch ;  c,  second,  or  honeycomb  stomach ;  d,  third  stomach, 
or  many-plies  j  e,  fourth  stomach  or  reed;  /,  pylorus. 

reverse  peristaltic  action  of  the  oesophagus;  this  return  takes  place  in 
a  very  regular  manner,  the  food  being  shaped  into  globular  pellets  by 
compression  within  a  sort  of  mould  formed  by  the  demi-canal,  and 
these  pellets  being  conveyed  to  the  mouth  at  regular  intervals,  appa- 
rently by  a  rhythmical  movement  of  the  oesophagus.  It  is  then  sub- 
jected to  a  prolonged  mastication  within  the  mouth  (the  **  chewing  of 
the  cud"),  by  which  it  is  thoroughly  triturated  and  impregnated  with 
saliva ;  after  which  it  is  again  swallowed  in  a  pulpy  semi-fluid  state. 
It  now  passes  along  the  groove  which  forms  the  continuation  of  the 
oesophagus,  without  opening  its  lips ;  and  is  thus  conveyed  into  the 
third  stomach,  whence  it  passes  to  the  fourth,  in  which  alone  the  true 
digestive  process  takes  place.  Now,  that  the  condition  of  the  food 
as  to  bulk  and  solidity,  is  the  circumstance  which  determines  the 
opening  or  closure  of  the  lips  of  the  groove,  and  which  consequently 
occasions  its  passage  into  the  first  and  second  stomachs,  or  into  the 
third  and  fourth,  appears  from  the  experiments  of  Flourens;  who 
found  that  when  the  food,  the  first  time  of  being  swallowed,  was  arti- 


270 


MOVEMENTS  OF  THE  STOMACH. 


Fig.  T3. 


ficially  reduced  to  a  soft  and  pulpy  condition,  it  passed  for  the  most 
part  along  the  demi-canal  into  the  third  stomach,  as  if  it  had  been 
ruminated, — only  a  small  portion  finding  its  way  into  the  first  and 
second  stomachs.  How  far  the  actions  of  this  curious  apparatus  are 
dependent  upon  nervous  influence, — or  how  far  they  are  due  to  the 
exercise  of  the  contractility  of  the  muscular  fibre,  directly  excited  by 
the  contact  of  the  substances  with  the  lining  membrane  of  the  tubes 
and  cavities, — has  not  yet  been  clearly  ascertained. 

458.  The  food,  when  introduced  into  the  Stomach,  and  submitted 
to  the  solvent  action  of  its  secretions,  is  also  subjected  to  a  peculiar 

movement,  which  is  eflfected  by 
the  muscular  walls  of  that  organ. 
The  purpose  of  this  motion  is 
obviously  to  keep  the  contents 
of  the  stomach  in  that  state  of 
constant  agitation,  which  is  most 
favourable  to  their  chemical  so- 
lution ;  and  particularly  to  bring 
every  portion  of  the  alimentary 
matter  into  contact  with  the  walls 
of  the  stomach,  so  as  to  be  sub- 
jected to  the  action  of  the  fluid, 
which  is  poured  forth  from  them 
during  the  digestive  process. 
The  movement  is  produced  by 
the  alternate  shortening  and  re- 
laxation of  the  various  fasciculi, 
which  are  disposed  in  almost 
every  direction  throughout  the 
muscular  wall  of  the  stomach  ; 
and  it  seems  to  produce  a  kind 
of  revolution  of  the  contents  of 
the  stomach,  sometimes  in  the 
direction  of  its  length,  and  some- 
times transversely.  Its  result  is 
well  shown  in  the  hair-balls, 
which  are  occasionally  found  in 
the  stomachs  of  animals,  that 
have  swallowed  hair  from  time 
to  time  through  licking  their 
skins ;  the  component  hairs  not 
being  pressed  together  confusedly,  but  being  worked  together  in 
regular  directions,  and  so  interwoven  that  they  cannot  be  readily 
separated.  As  digestion  proceeds,  the  dissolved  fluid  escapes,  little 
by  little,  through  the  pyloric  orifice,  which  closes  itself  firmly  against 
the  passage  of  solid  bodies  ;  and  this  motion  continues,  until  the  sto- 
mach is  completely  emptied  ;  when  it  ceases,  until  food  is  again  in- 
troduced.    The  bulk  of  the  alimentary  mass  diminishes  rapidly,  as 


Section  of  part  of  the  Stomach  of  the  Sheep,  to 
show  the  demi-canal  of  the  oesophagus ;  the  mucous 
membrane  is  for  the  most  part  removed,  to  show  the 
arrangement  of  the  muscular  fibres.  At  a  is  seen 
the  termination  of  the  ossophageal  tube,  the  cut  edge 
of  whose  mucous  membrane  is  shown  at  b.  The 
lining  of  the  first  stomach  is  shown  at  c^c;  and  the 
mucous  membrane  of  the  second  stomach  is  seen 
to  be  raised  from  the  subjacent  fibres  at  d.  At  e,  e, 
the  lips  of  the  demi-canal  are  seen  bounding  the 
groove,  at  the  lower  end  of  which  is  the  entrance 
to  the  third  stomach  or  many-plies. 


MOVEMENTS  OF  THE  INTESTINAL  CANAL.  271 

the  solvent  process  is  near  its  completion  ;  and  the  separation  of  the 
fluid  product  or  chyme  is  aided  by  a  peculiar  action  of  the  transverse 
fasciculi,  which  surrounds  the  stomach  at  about  four  inches  from  its 
pyloric  extremity.  These  shorten  in  such  a  manner,  as  to  produce  a 
sort  of  hour-glass  separation  between  the  portions  of  the  stomach  on 
either  side  of  it  ;  and  the  fluid  solution,  being  received  by  the  pyloric 
or  smaller  portion,  is  pumped  away  through  the  pylorus ;  whilst  the 
solid  matter  yet  undissolved  is  retained  in  the  larger  division. 

459.  The  degree  in  which  these  movements  are  dependent  upon 
the  nervous  system,  or  are  under  its  control  or  direction,  has  not  yet 
been  clearly  ascertained.  Distinct  movements  may  be  excited  in  the 
stomach  of  a  Rabbit,  if  it  be  distended  with  food,  by  irritating  the 
par  vagum  soon  after  the  death  of  the  animal ;  these  movements 
seem  to  commence  from  the  cardiac  orifice,  and  then  to  spread  them- 
selves peristaltically  along  the  walls  of  the  stomach  ;  but  no  such 
movements  can  be  excited  if  the  stomach  be  empty.  On  the  other 
hand,  there  is  distinct  proof,  that  all  the  movements  necessary  to  di- 
gestion may  take  place  after  the  section  of  that  nerve  ;  although  the 
first  effect  of  the  operation  appears  to  be  to  suspend  them  completely. 
It  is  probable  that  the  movements  of  the  stomach  are  more  regular 
and  energetic  in  Herbivorous  animals,  whose  food  is  difficult  of  di- 
gestion, than  they  are  in  the  Carnivora,  whose  aliment  is  dissolved 
with  comparative  facility. 

460.  From  the  time  that  the  ingested  matter  enters  the  Intestinal 
tube,  it  is  propelled  onwards  by  the  peristaltic  contractions  of  its  mus- 
cular coat ;  which  are  excited,  independently  of  all  nervous  influence, 
by  the  contact  of  the  aliment,  or  by  that  of  the  secretions  mingled 
with  it  in  its  passage  along  the  canal.  These  last  appear  to  have  an 
important  effect ;  for  we  find  that,  when  the  bile-duct  is  tied,  so  as  to 
prevent  the  bile  from  entering  the  intestine,  constipation  always  oc- 
curs ;  whilst  an  increase  of  the  biliary  and  other  secretions,  consequent 
upon  the  action  of  mercury  or  upon  any  other  cause,  produces  an 
increased  peristaltic  movement,  and  a  more  rapid  discharge  of  the 
excrementitious  matter.  During  the  passage  of  the  alimentary  matter 
along  the  small  intestine,  as  we  shall  see  hereafter,  a  large  proportion 
of  its  fluid  is  removed,  by  the  absorbent  power  of  the  villi ;  and  the 
residue  is  again  brought,  therefore,  to  a  more  solid  consistence.  This 
residue  consists  in  part  of  those  portions  of  the  aliment,  which  are 
not  capable  of  being  dissolved  or  finely  divided,  so  as  to  be  received 
by  the  absorbents ;  and  in  part  of  the  matters  poured  into  the  ali- 
mentary canal,  by  the  various  glands  that  discharge  their  contents  into 
it,  for  the  purpose  of  being  carried  out  of  the  body.  The  feces, 
which  are  thus  formed,  are  propelled  through  the  large  intestine,  by 
the  continued  peristaltic  action  of  its  walls,  until  they  arrive  at  the 
rectum. 

461.  That  the  ordinary  peristaltic  action  of  the  intestinal  canal  is 
independent  of  nervous  influence,  is  suflficiently  proved  by  the  fact, 
that  it  will  continue  when  the  tube  is  completely  separated  from  all 


272  DEFECATION. 

connection  with  the  nervous  centres;  as  well  as  by  the  difficulty, 
already  adverted  to  (§  353),  of  exciting  contractions  in  the  muscular 
coat  by  any  stimulation  of  its  nerves.  All  the  nerves  of  the  intestine, 
from  its  commencement  at  the  pyloric  orifice  of  the  stomach  to  its  ter- 
mination at  the  anus,  are  derived  from  the  ganglia  of  the  sympathetic 
system  ;  but  there  is  evidence  that  those  which  influence  its  movements 
are  really  derived  from  the  spinal  cord  (see  Chap.  XII).  Although 
the  will  has  no  influence  whatever  on  the  peristahic  movement,  yet 
the  emotions  seem  to  affect  it ;  and  it  is  probably  to  convey  their  influ- 
ence that  the  intestinal  canal  is  supplied  with  motor  nerves.  It  is 
also  furnished  with  sensory  nerves,  which  form  part  of  the  trunks  of 
the  sympathetic  system,  but  which  really  pass  onwards  to  the  brain; 
these  do  not,  however,  make  us  conscious  of  the  passage  of  the  ali- 
mentary matter  along  the  canal,  so  long  as  it  is  in  a  state  of  health ; 
but  in  various  diseased  conditions,  they  give  rise  to  sensations  of  the 
most  painful  nature. 

462.  For  the  occasional  discharge  of  the  feces  from  the  rectum,  and 
for  the  retention  of  them  at  other  times,  we  find  the  outlet  or  anal 
orifice,  provided  with  an  additional  muscular  apparatus,  which  is  con- 
nected with  the  spinal  system  of  nerves.  The  act  of  defecation  is  due 
tothe  pressure  upon  the  contents  of  the  rectum,  which  is  occasioned  by 
the  combined  contraction  of  the  diaphragm  and  the  abdominal  muscles; 
whilst,  on  the  other  hand,  the  retention  of  the  feces  is  due  to  the  con- 
tractile power  of  the  sphincter  muscle,  which  surrounds  the  anus.  The 
action  of  the  sphincter  ani,  like  that  of  the  sphincter  of  the  cardia,  is  a 
reflex  one;  dependent  upon  the  connection  of  the  muscle,  by  excitor 
and  motor  nerves,  with  the  spinal  cord.  If  the  lower  portion  of  the  cord 
be  destroyed,  or  if  the  nerves  be  divided,  the  sphincter  loses  its  con- 
tractile power,  and  becomes  flaccid.  When  in  proper  action,  however, 
its  power  is  sufficient  to  prevent  the  escape  of  the  contents  of  the  rec- 
tum ;  until  the  expulsive  force  becomes  very  strong,  in  consequence 
either  of  the  quantity  of  feces  which  has  accumulated,  or  the  acridity 
of  their  character.  In  either  case,  the  impression  made  upon  the  mu- 
cous membrane  of  the  rectum  is  conveyed  to  the  spinal  cord  ;  and,  by 
a  reflex  motor  impulse,  the  muscles  of  defecation  are  thrown  into  com- 
bined action,  the  resistance  of  the  sphincter  is  overcome,  and  the  feces 
are  expelled.  An  unduly  irritable  state  of  the  mucous  membrane,  or 
a  disordered  state  of  the  excrementitious  matter  (resulting  from  the 
irritating  character  of  the  substances  swallowed,  from  the  acrid  charac- 
ter of  the  secretions  poured  into  the  canal,  or  from  an  unusual  change 
in  the  aliment  during  the  digestive  process),  may  occasion  unduly  fre- 
quent calls  upon  the  muscles  of  defecation,  which  the  sphincter  is 
unable  to  resist.  On  the  other  hand,  if  the  progress  of  the  feces  be 
delayed  in  the  large  intestines,  by  deficient  peristaltic  movement,  they 
accumulate  higher  up,  and  the  act  of  defecation  is  not  excited. 

463.  Although  the  sphincter  ani  on  the  one  hand,  and  the  muscles 
of  defecation  on  the  other,  are  called  into  action  by  the  reflex  power 
of  the  spinal  cord,  and  are  so  far  involuntary  in  their  operation,  yet 
they  are  also  in  some  degree  subject  (in  Man  at  least)  to  the  influence 


MUCOUS  SECRETION.  273 

of  the  will.  The  resistance  of  the  sphincter  may  be  increased  by  a 
voluntary  effort,  when  it  is  desired  to  retain  the  feces  in  opposition  to 
the  power  of  the  expulsors;  and  it  is  only  when  the  latter  operate 
with  excessive  force  that  they  can  overcome  it.  On  the  other  hand, 
the  expulsors  may  be  called  into  action,  or  maybe  aided,  by  the  will, 
when  the  stimulus  to  their  movement  received  through  the  spinal  cord, 
would  not  otherwise  be  strong  enough ;  and  the  feces  may  thus  be 
evacuated  by  a  voluntary  effort,  at  a  time  when  they  would  not  other- 
wise be  discharged. 

4.   Of  the  Secretions  poured  into  the  Alimentary  Canal,  and  of  Changes 
which  they  effect  in  its  contents, 

464.  The  whole  Mucous  Membrane  of  the  Alimentary  canal,  from 
the  mouth  to  the  anus,  is  covered  during  health  with  that  peculiar 
viscid  secretion  termed  mucus,  of  which  the  characters  have  been 
already  described  (§  237).  This  is  formed,  partly,  on  the  free  sur- 
face of  the  membrane  itself,  but  chiefly  in  the  numerous  follicles  or 
depressions  by  which  that  surface  is  increased ;  and  it  appears  de- 
stined for  the  protection  of  the  delicate,  highly  vascular  membrane 
from  undue  irritation  by  the  contact  of  the  substances,  which  are  passing 
through  the  alimentary  tube.  When  these  are  unusually  acrid,  the 
secretion  of  mucus  is  augmented  in  quantity,  and  is  increased  in  vis- 
cidity, so  as  to  form  an  effective  sheath  to  the  membrane,  which  would 
otherwise  suffer  severely.  When  this  secretion  is  deficient,  the  mem- 
brane is  irritated  by  the  contact  of  any  but  the  blandest  substances  ; 
and  the  class  of  remedies  termed  demulcents  are  useful  in  coating  and 
protecting  it. 

465.  During  the  mastication  of  the  food  in  the  mouth,  the  Salivary 
secretion  is  poured  in,  for  the  purpose  of  being  mingled  with  it,  and  of 
rendering  the  act  of  mastication  more  easy.  This  secretion  is  formed 
by  three  pairs  of  glands, — the  Parotid,  the  Sub-lingual,  and  the  Sub- 
maxillary;   these   are   composed  of  minute 

follicles,  whose  diameter  is  about  1-lOOOth  Fig. 74. 

of  an  inch,  connected  together  by  branches 
of  their  ducts,  upon  which  they  are  set  like 
grapes  upon  their  stalk,  surrounded  by  a 
plexus  of  blood-vessels,  and  bound  together 
by  areolar  tissue.  Within  the  follicles  are 
the  true  secreting  cells  (§  238);  by  whose 
growth  and  development,  the  material  of  the 
secretion  is  separated  from  the  blood.  These 
salivary  cells  are  often  to  be  recognized  in 
the  saliva;  they  must  not,  however,  be  con- 
founded with  the  epithelium  cells  of  the 
mucous  membrane  of  the  mouth,  which  are  Lobuie  of  Parotid  Giand  of 
much  larger.  The  fluid  obtained  from  the  "^Z^^^'i^Z" 
mouth  is  not  pure  saliva ;  for  the  mucus  of 
18 


274  SALIVARY  GLANDS  AND  THEIR  SECRETIONS. 

the  mouth  itself  is  mingled  with  the  secretion  from  the  salivary 
glands.  If  the  proportion  of  the  former  be  considerable,  it  gives  to 
the  fluid  of  the  mouth  an  acid  reaction ;  whilst  if  the  latter  be  pre- 
dominant (which  it  is  directly  before,  and  during  the  act  of  eating), 
the  fluid  of  the  mouth  has  an  alkaline  reaction.  It  may  be  some- 
times observed,  that  the  saliva  of  the  mouth  will  strike  a  blue  colour 
with  reddened  litmus  paper,  whilst  it  turns  blue  litmus  paper  red ; 
thus  showing  the  presence  both  of  an  acid  and  an  alkali  in  a  state  of 
imperfect  neutralization. 

466.  The  solid  matter  of  the  Salivary  secretion  is  about  1  per  cent, 
of  the  whole ;  and  this  consists  in  part  of  animal  principles,  and  in 
part  of  saline  substances.  The  animal  matter  consists  of  osmazome, 
mucus,  and  a  peculiar  substance  termed  ptyaline  or  salivary  matter ; 
which  is  soluble  in  water  and  insoluble  in  alcohol,  and  which  is  yet 
different  from  both  albumen  and  gelatin.  This  substance  appears  to 
have  a  decided  effect  in  producing  the  metamorphosis  of  certain  ali- 
mentary substances,  on  which  it  acts  like  2i  ferment.  Starch  may  be 
converted  into  sugar,  and  sugar  into  lactic  acid,  by  its  agency ;  and, 
if  concentrated,  it  has  a  certain  solvent  power  for  casein,  animal 
flesh,  and  other  proteine-compounds.  Its  chemical  nature  has  not 
yet  been  precisely  determined.  The  saline  constituents  of  the  Saliva 
are  nearly  identical  with  those  of  the  blood ;  the  chlorides  of  sodium 
and  potassium  form  considerably  more  than  half;  and  the  remainder 
consists  chiefly  of  the  tribasic  phosphate  of  soda,  to  which  the  alka- 
line reaction  of  the  fluid  is  due,  with  the  phosphates  of  lime,  magnesia, 
and  iron.  It  is  of  the  earthy  phosphates,  that  the  tartar  which  col- 
lects about  the  teeth  is  chiefly  composed  ;  the  particles  of  these  being 
held  together  by  about  20  per  cent,  of  animal  matter:  and  the  compo- 
sition of  the  concretions,  which  occasionally  obstruct  the  salivary 
ducts,  is  nearly  the  same. 

467.  The  quantity  of  Saliva  formed  during  the  twenty-four  hours, 
has  been  estimated  at  from  15  to  20  ounces ;  but  on  this  point  it  is 
impossible  to  speak  with  certainty.  The  secretion  is  by  no  means 
constantly  flowing;  indeed  it  is  almost  entirely  suspended,  when  the 
masticator  muscles  and  tongue  are  at  perfect  rest,  unless  it  be  excited 
by  any  mental  cause ;  and  hence  it  is,  that  the  mouth  becomes  dry 
during  sleep,  if  it  be  not  kept  closed.  The  flow  of  Saliva  takes  place 
just  when  it  is  most  wanted;  that  is,  w^hen  food  has  been  taken  into 
the  mouth,  and  when  the  operation  of  mastication  is  going  on.  But 
it  will  also  take  place,  especially  in  a  hungry  person,  at  the  sight,  or 
even  at  the  idea,  of  savoury  food ;  as  is  implied  by  the  common  ex- 
pression of  the  "  mouth  watering"  for  such  an  object.  The  influence 
thus  exercised  over  it  by  the  emotional  state  of  the  mind,  is  probably 
conveyed  to  the  salivary  glands  by  the  Fifth  pair ;  which  contains 
many  of  the  gray  or  organic  filaments ;  and  which  seems  to  take  the 
place,  in  the  Head,  of  a  distinct  lymphatic  system. 

468.  Having  been  conveyed  into  the  Stomach,  the  food  is  sub- 
mitted to  the  action  of  the  Gastric  Fluid,  which  is  secreted  in  the 


GASTRIC  FOLLICLES  AND  THEIR  SECRETION. 


275 


walls  of  that  organ.  This  fluid  is  not  present  in  the  empty  stomach  ; 
its  secretion  being  excited  by  the  presence  of  food,  or  by  the  irritation 
of  the  walls  of  the  organ  by  some  solid  body.  In  the  intervals  be- 
tween the  digestive  process,  the  mucous  membrane  is  of  a  light  pink 
hue;  but  it  becomes  more  turgid  with  blood,  when  the  presence  of 
food  calls  for  the  activity  of  its  secreting  processes.  It  is  of  a  soft 
and  velvet-like  appearance  ;  and  it  is  constantly  covered  with  a  very 
thin  transparent  viscid  mucus,  which  has  neither  acid  nor  alkaline 
reaction.  By  applying  aliment  or  other  stimulants  to  the  internal  coat 
of  the  stomach,  and  by  observing  the  effect  through  a  magnifying 
glass,  numerous  minute  papillae  can  be  seen  to  erect  themselves  upon 
the  mucous  membrane,  so  as  to  rise  through  the  coating  of  mucus ; 
and  from  these  is  poured  forth  a  pure,  limpid,  colourless,  slightly 
viscid  fluid,  having  a  distinctly  acid  reaction,  which  is  the  Gastric 
juice.  This  fluid  is  secreted  by  follicles,  which  are  lodged  in  the 
walls  of  the  stomach,  and  which  closely  resemble  those  that  else- 
where secrete  mucus  ;  but  they  are  usually  of  more  complex  structure, 
and  are  more  numerous. 

469.  If  the  Mucous  Membrane  of  the  stomach  be  divided  by  a 
section  perpendicular  to  its  walls,  it  is  seen  to  be  made  up,  as  it  were^ 
of  tubular  follicles  closely  applied  to  each  other  ;  their  blind  extremi- 
ties resting  upon  the  submucous  tissue,  and  their  open  ends  being  di- 
rected towards  the  cavity  of  the  stomach.  In  some  situations,  these 
tubuli  are  short  and  straight ;  in  other  parts  they  are  longer,  and 
present  an  appearance  of  irregular  dilatation  or  partial  convolution 
(Fig.  75,  1).  This  is  their  usual  character,  especially  near  the  car- 
diac orifice  of  the  stomach  ;  but  near  the  pyloric  orifice  they  have  a 
much  more  complex  structure  (Fig.  75,  2).  These  tubular  follicles- 
are  arranged  in  bundles  or  groups,  and  are  surrounded  and  bound 


Fig,  75. 


Fig. 


Glandulac  from  the  coats  of  the  stomach,  magnified  45 
diameters; — 1,  from  the  middle  of  the  stomach;  2,  from 
the  neighbourhood  of  the  pylorus. 


Portion  of  the  mucous  mem- 
brane of  the  stomach,  showing 
the  entrances  to  its  secreting 
tubes,  in  pits  upon  its  surface. 


together  by  a  fine  areolar  membrane  ;  and  this  also  serves  to  convey 
vessels  from  the  submucous  tissue,  which  ramify  among  the  follicles, 
and  supply  the  materials  for  their  secretion.  The  number  of  tubuli 
in  each  group  is  by  no  means  constant.  The  follicles  do  not,  in 
general,  open  directly  upon  the  surface ;  but  into  the  bottom  of  small 


276  PROPERTIES  OF  GASTRIC  FLUID  AND  OF  PEPSINE. 

depressions  or  pits,  which  may  be  seen  to  cover  the  membrane. 
These  pits  are  more  or  less  circular  in  form  ;  and  are  separated  from 
one  another  by  membranous  partitions,  which  vary  in  depth,  and  some- 
times by  pointed  processes,  which  are  capable  of  erecting  themselves 
in  the  manner  just  described.  The  diameter  of  these  pits  varies 
from  about  1- 100th  to  l-250th  of  an  inch  ;  it  is  always  greatest  near 
the  pylorus.  The  number  of  the  gastric  follicles  opening  into  each, 
is  usually  from  three  to  five ;  but  there  are  sometimes  more. 

470.  The  chemical  composition  of  the  Gastric  fluid  has  been  a  sub- 
ject of  much  discussion,  and  can  scarcely  yet  be  regarded  as  deter- 
mined. Possibly  it  may  vary  in  its  nature,  according  to  the  state  of 
the  system,  and  the  kind  of  animal  from  which  it  is  obtained.  That 
of  Man  has  been  usually  stated  to  contain  a  sensible  quantity  of  un- 
combined  Muriatic  and  Acetic  acids,  to  which  its  acid  reaction  has 
been  attributed  ;  whilst,  on  the  other  hand,  it  has  been  recently  as- 
serted, that  the  gastric  fluid  of  the  Dog  contains  no  free  muriatic  acid, 
and  that  its  acid  reaction  is  due  to  the  presence  of  the  superphosphate 
of  lime.  The  other  inorganic  ingredients  of  the  Gastric  fluid  are 
Eearly  the  same  as  those  of  the  Saliva.  It  contains  a  peculiar  organic 
compound,  which,  like  Ptyaline,  bears  a  considerable  resemblance  to 
albumen,  but  which  is  not  identical  with  it ;  to  this  the  name  of  Pep- 
sine  has  been  given.  The  properties  of  Pepsine  have  been  principally 
studied  in  that  form  of  it  obtained  from  the  mucous  membrane  of  the 
stomach  of  the  Pig,  which  bears  a  close  resemblance  to  that  of  Man. 
When  this  membrane  is  digested  in  a  large  quantity  of  warm  water, 
it  is  purified  from  the  various  soluble  substances  it  may  contain  ;  but 
the  pepsine  is  not  taken  up,  as  it  is  not  soluble  in  warm  water.  By 
continuing  the  digestion  in  cold  water,  the  pepsine  is  then  extracted 
nearly  pure.  When  this  solution  is  evaporated  to  dryness,  there  re- 
mains a  brown,  grayish,  viscid  mass,  having  the  appearance  of  an 
extract,  and 'the  odour  of  glue.  A  similar  substance  may  be  obtained 
by  adding  strong  alcohol  to  a  fresh  solution  of  pepsine ;  for  the  latter 
is  then  precipitated  in  white  flocks,  which  may  be  collected  on  a  filter, 
and  which  produce  a  gray  compact  mass  when  dried.  Pepsine  enters 
into  chemical  combination  with  many  acids;  forming  compounds 
which  still  ;Fedden  litmus  paper ;  and  this  appears  to  be  its  condition 
in  the  gastric  juice. 

471.  The  (muriate  ;and  acetate  of  pepsine  possess  a  very  remarkable 
solvent  power  for  albuminous  substances.  A  liquid  which  contains 
only  17  ten-thousandths  of  acetate  of  pepsine,  and  6  drops  of  muriatic 
acid  per  ounce,  possesses  solvent  power  enough  to  dissolve  a  thin 
slice  of  coagulated  albumen,  in  the  course  of  six  or  eight  hours'  diges- 
tion. With  12  drops  of  muriatic  acid  per  ounce,  the  same  quantity 
of  white  of  egg  is  dissolved  in  two  hours.  A  liquid  which  contains 
only  half  a  grain  of  acetate  of  pepsine,  and  to  which  muriatic  acid  and 
white  of  egg  are  alternately  added,  so  long  as  the  latter  is  dissolved, 
is  capable  of  taking  up  210  grains  of  coagulated  white  of  egg,  at  a 
temperature  between  95^  and  104.°     The  same  acid  with  pepsine 


ACTION  OF  GASTRIC  FLUID— CHYME.  277 

dissolved  blood,  fibrin,  meat,  and  cheese;  whilst  the  acid  without 
the  pepsine  requires  a  very  long  time  to  do  so  at  ordinary  temperatures. 
Very  dilute  muriatic  acid,  however,  at  the  boiling  point,  dissolves 
these  albuminous  substances  ;  and  the  solution  has  the  same  charac- 
ters as  that  which  is  made  by  the  agency  of  pepsine.  The  horny 
tissues, — such  as  the  epidermis,  horn,  hair,  &c., — and  the  yellow 
fibrous  tissue,  are  not  affected  by  the  acid  solution  of  pepsine.  It 
appears  from  these  experiments,  that  the  muriatic  acid  is  the  real 
solvent ;  and  that  the  action  of  the  pepsine  is  limited  to  disposing  the 
albuminous  matter  for  solution,  producing  in  it  a  change  analogous  to 
that  which  may  be  effected  by  heat.  Hence  it  may  be  considered, 
like  ptyaline,  as  a  sort  o{ ferment ;  its  office  being  to  produce  a  tend- 
ency to  change,  in  the  substances  on  which  it  acts,  without  itself 
entering  into  new  combinations  with  any  of  their  elements. 

472.  These  experiments  appear  to  afford  an  explanation  of  the 
properties  of  the  gastric  fluid,  as  ascertained  by  direct  experiment 
upon  it.  When  drawn  direct  from  the  human  stomach,  it  is  found  to 
possess  the  power  of  dissolving  various  kinds  of  alimentary  substances, 
whilst  these  are  submitted  to  its  action  at  a  constant  temperature  of 
100°  (which  is  about  that  of  the  stomach),  and  are  frequently  agitated. 
The  solution  appears  to  be  in  all  respects  as  perfect  as  that  which 
naturally  takes  place  in  the  stomach  ;  but  a  longer  time  is  required  to 
make  it.  This  is  easily  accounted  for  by  the  difference  of  the  condi- 
tions ;  for  no  ordinary  agitation  can  produce  the  same  effect  with  the 
curious  movements  of  the  stomach  (§  458);  fresh  gastric  fluid  is 
poured  out,  as  it  is  wanted,  during  the  natural  process  of  digestion  ; 
and  the  continual  removal  of  the  matter  which  has  been  already  dis- 
solved by  its  exit  through  the  pylorus,  is  of  course  favourable  to  the 
action  of  the'  solvent  upon  the  remainder.  The  quantity  of  food, 
which  a  given  amount  of  gastric  fluid  can  dissolve,  is  limited  ;  pre- 
cisely as  in  the  case  of  the  acidulous  solution  of  pepsine.  The 
marked  influence  of  temperature  upon  its  action  is  shown  by  the  fact, 
that  fresh  gastric  fluid  has  scarcely  any  influence  on  the  matter  sub- 
mitted to  it,  when  the  bottle  is  exposed  to  cold  air,  instead  of  being 
kept  at  a  temperature  of  100°.  Hence  the  use  of  a  large  quantity  of 
cold  water  at  meal-times,  or  of  ice  afterwards,  must  retard  the  diges- 
tive process. 

473.  The  pulpy  substance,  which  is  the  product  of  the  reducing 
action  of  the  gastric  juice,  is  termed  Chyme.  Its  consistence  will  of 
course  vary,  in  some  degree,  with  the  relative  quantity  of  solids  and 
liquids  ingested.  In  general  it  is  grayish,  semifluid,  and  homoge- 
neous ;  and  possesses  a  slightly  acid  taste,  but  is  otherwise  insipid. 
When  the  food  has  been  of  a  rich  oily  character,  the  Chyme  possesses 
a  creamy  aspect ;  but  when  it  has  contained  a  large  proportion  of  fari- 
naceous matter,  it  has  rather  the  appearance  of  gruel.  The  state  in 
which  the  various  alimentary  principles  exist  in  it,  has  not  yet  been 
accurately  determined  ;  the  following,  however,  may  be  near  the  truth. 
— The  proteine-corapounds,  whether  derived  from  Animal  or  Vege- 


278  SECRETION  OF  GASTRIC  FLUID. 

table  food,  are  all  reduced  to  the  condition  of  Albumen ;  a  part  of 
which  is  dissolved^  whilst  another  portion  is  suspended  in  a  very  finely- 
divided  state. — Gelatin  will  be  dissolved  or  not,  according  to  its 
previous  condition  ;  if  it  exist  in  a  tissue  from  which  it  cannot  readily 
be  extracted,  it  will  pass  forth  almost  unchanged  ;  but  when  ingested 
in  a  state  of  solution,  it  remains  so ;  and  if  it  have  been  previously 
prepared  for  solution  by  boiling,  its  solution  is  completed  in  the  sto- 
raach. — The  Gummy  matters  of  Vegetables  are  dissolved,  when  they 
exist  in  a  soluble  form  ;  as  in  the  case  of  pure  gum,  pectine,  and  dex- 
trine or  starch-gum.  The  degree  in  which  Starch,  when  its  vesicles 
have  not  been  ruptured  by  heat,  is  affected  by  the  gastric  fluid,  seems 
to  differ  in  different  animals ;  the  Ruminants  and  Granivorous  Birds 
apparently  possessing  the  power  of  crushing  or  dissolving  the  enve- 
lops of  the  starch-globules,  whilst  they  pass  through  the  alimentary 
canal  of  other  Herbivora  unchanged,  and  may  be  detected  entire  in  their 
excrements. — Sugar  is  unquestionably  taken  up  in  solution,  as  such, 
in  a  healthy  condition  of  the  system ;  but  it  may  undergo  a  previous 
change  in  the  stomach,  in  disordered  states  of  the  digestive  process. — 
Oily  matters,  whether  of  Animal  or'Vegetable  origin,  are  reduced  to 
the  condition  of  an  emulsion ;  being  very  finely  divided,  and  their 
particles  diffused  through  the  chyme. — Most  other  substances,  as 
resins,  woody  fibre,  horny  matter,  yellow  fibrous  tissue,  &c.,  pass 
unchanged  from  the  stomach,  and  undergo  no  subsequent  alteration 
in  the  intestinal  canal ;  so  that  they  are  discharged  among  the  feces 
as  completely  useless. 

474.  We  have  now  to  notice  the  conditions,  under  which  the  Gas- 
tric fluid  is  secreted  ;  the  knowledge  of  which  is  of  great  practical 
importance.  We  have  seen  that  it  is  not  poured  forth,  except  when 
food  is  introduced  into  the  stomach,  or  when  its  walls  are  irritated  in 
some  other  mode  ;  and  there  is  reason  to  believe,  that  it  is  not  pre- 
viously secreted  and  stored  up  in  the  follicles,  but  that  the  act  of  secre- 
tion itself  is  due  to  the  stimulus  applied  to  the  mucous  membrane. 
The  quantity  of  the  fluid  then  poured  into  the  stomach,  however,  is 
not  regulated  by  the  amount  of  food  ingested,  so  much  as  by  the 
wants  of  the  system  ;  and  as  only  a  definite  quantity  of  food  can  be 
acted  on  by  a  given  amount  of  gastric  juice,  any  superfluity  remains 
undissolved  for  some  time, — either  continuing  in  the  stomach  until  a 
fresh  supply  of  the  solvent  is  secreted,  or  passing  into  the  intestinal 
canal  in  a  crude  state,  and  becoming  a  source  of  irritation,  pain,  and 
disease.  The  use  of  a  small  quantity  of  salt,  pepper,  mustard,  or 
other  stimulating  substances,  appears  to  produce  a  gently  stimulating 
effect  upon  the  mucous  membrane,  and  by  causing  an  increased. afflux 
of  blood,  to  augment  the  quantity  of  the  gastric  fluid  poured  forth. 
Any  excess  of  these  or  other  irritants,  however,  produces  a  disordered 
condition  of  the  mucous  membrane,  which  is  very  unfavourable  to  the 
digestive  process.  It  becomes  red  and  dry,  with  an  insufficient  secre- 
tion of  mucus;  the  epithelial  lining  is  abraded,  so  that  the  mucous 
-coat  is  left  entirely  bare  ;  and  irregular  circumscribed  patches  of  a 


PRODUCTION  OF  CHYME— ADMIXTURE  OF  BILE.  279 

deeper  hue,  sometimes  with  small  aphthous  crusts,  present  them- 
selves here  and  there  on  the  walls  of  the  stomach.  Similar  results 
follow  excess  in  eating.  When  these  changes  are  inconsiderable,  the 
appetite  is  not  much  impaired,  the  tongue  does  not  indicate  disorder, 
and  the  digestive  process  may  be  performed  ;  but  if  they  proceed 
further,  dryness  of  the  mouth,  thirst,  accelerated  pulse,  foulness  of  the 
tongue,  and  other  symptoms  of  febrile  irritation,  manifest  themselves  ; 
and  no  gastric  secretion  can  then  be  excited  by  the  stimulus  of  food. 
Similar  results  may  follow  the  excitement  of  the  emotions  ;  and  those 
of  a  depressing  nature  seem  especially  to  produce  a  pale  flaccid  con- 
dition of  the  mucous  membrane,  which  is  equally  unfavourable  to  the 
due  secretion  of  gastric  fluid. 

475.  That  the  amount  of  the  secretion  is  ordinarily  proportioned  to 
the  wants  of  the  system, — that  the  introduction  of  any  superfluous 
aliment  into  the  stomach  is  not  only  useless  but  injurious,  as  giving 
rise  to  irritation, — that  incipient  disorder  of  the  stomach  may  occur, 
rendering  it  less  fit  than  usual  for  the  discharge  of  its  important  duties, 
without  manifesting  itself  by  the  condition  of  the  tongue, — that  when 
the  tongue  does  indicate  disorder  of  the  stomach,  such  disorder  is 
usually  considerable, — and  that  every  particle  of  food  ingested,  in 
such  states  as  prevent  the  secretion  of  gastric  fluid,  is  a  source  of  fresh 
irritation, — are  truths  which  cannot  be  too  constantly  kept  in  mind. 
There  can  be  no  doubt  that  the  habit  of  taking  more  food  than  the 
system  requires,  is  a  very  prevalent  one  ;  and  that  it  is  persevered  in 
because  no  evil  result  seems  to  follow.  But  when  it  is  borne  in  mind 
that  this  habit  must  keep  the  stomach  in  a  state  of  continual  irritation, 
however  slight,  it  can  scarcely  be  doubted  that  the  foundation  is  thus 
laid  for  future  disorder,  of  a  more  serious  kind.  Two  circumstances 
especially  tend  to  maintain  this  practice  in  adults,  independently  of 
the  mere  disposition  to  gratify  the  palate.  One  is  the  habit  of  eating 
the  same  amount  of  food,  as  during  the  period  of  growth,  when  more 
was  required  by  the  system.  The  other  is  the  custom  of  eating  too 
fast ;  and  this  is  injurious, — both  by  preventing  sufficient  mastication, 
and  thus  throwing  on  the  stomach  more  than  its  proper  duty, — and 
also  by  causing  an  over-supply  of  food  to  be  ingested,  before  there  is 
time  for  the  feeling  of  satisfaction  to  replace  that  of  hunger  (§  486). 

476.  The  Chyme,  upon  quitting  the  stomach,  passes  into  the  duo- 
denum ;  where  it  is  mingled  with  the  biliary  and  pancreatic  secretions. 
The  secretion  of  Bile  is  evidently  a  process  of  the  highest  importance 
in  the  economy ;  as  we  may  judge  alike  from  the  size  of  the  liver  and 
the  supply  of  blood  it  receives,  and  from  the  rapidly  fatal  effects  of 
its  suspension.  Yet  the  chemical  nature  of  the  secretion  has  not  yet 
been  satisfactorily  determined;  and  the  destination  of  the  fluid  is  still 
a  matter  of  doubt.  That  a  large  part  of  it  is  purely  excrementitious, 
and  is  poured  into  the  intestinal  tube  for  the  purpose  of  being  carried 
out  of  the  body,  can  scarcely  be  questioned  ;  but  there  is  strong  evi- 
dence, that  a  part  of  it  is  destined  to  be  absorbed  again,  after  per- 
fo  rming  some  action  of  importance  upon  the  contents  of  the  alimentary 


280  SECRETION  OF  BILE. 

canal.  There  is  a  probability  that  a  part  of  its  function  consists  in 
rendering  the  fatty  matter  of  the  aliment  more  soluble ;  the  nature  of 
the  secretion  being  such,  as  to  give  it  in  some  degree  the  action  of 
a  soap.  When  fresh  bile  is  mingled  with  newly-formed  chyme,  in 
a  glass  vessel,  the  mixture  separates  into  three  distinct  parts ; — a 
reddish-brown  sediment  at  the  bottom, — a  whey-coloured  fluid  in 
the  centre, — and  a  creamy  pellicle  at  the  top.  The  central  and 
upper  strata  probably  constitute  the  portion  which  is  destined  for 
absorption;  whilst  the  sediment,  partly  consisting  of  the  unreducible 
portion  of  the  food,  and  partly  of  the  biliary  matter  itself,  is  evidently 
excrementitious. 

477.  The  composition  of  the  Bile,  and  the  structure  of  the  organ 
which  elaborates  it,  will  be  more  fitly  considered  when  the  Excre- 
tions in  general  are  treated  of  (Chap.  IX.) ;  at  present  we  have  only 
to  consider  its  relation  to  the  digestive  process.  In  all  but  the  very 
lowest  animals,  we  find  traces  of  a  bile-secreting  apparatus;  and  this 
is  almost  constantly  situated  in  the  immediate  neighbourhood  of  the 
stomach.  In  many  cases,  the  secretion  is  poured  directly  into  the 
cavity  of  that  organ ;  but  in  most,  it  is  conveyed  (as  in  Man)  into  the 
intestinal  tube  near  its  commencement.  There  are  few  instances  in 
which  the  bile-ducts  discharge  themselves  into  the  intestine  low  down, 
and  still  fewer  in  which  they  terminate  near  its  outlet ;  and  in  these 
last,  they  appear  also  to  discharge  the  functions  of  urinary  organs. 
Hence  it  seems  clear,  from  the  disposition  of  the  biliary  apparatus, 
that  it  has  a  purpose  to  serve  in  connection  with  the  digestive  func- 
tion, and  is  not  destined  solely  for  the  elaboration  of  a  product  which 
is  to  be  cast  out  of  the  body;  since,  if  the  latter  were  the  case,  that 
product  would  be  carried  out  immediately,  like  the  urinary  excretion, 
and  would  not  be  discharged  into  the  alimentary  canal  high  up. — This 
conclusion  is  confirmed  by  experiment ;  for  it  has  been  shown  by  the 
recent  experiment  of  Schwann,  that,  if  the  bile-duct  be  divided,  and 
be  made  to  discharge  its  contents  externally  through  a  fistulous  ori- 
fice in  the  walls  of  the  abdomen,  instead  of  into  the  intestinal  canal, 
those  animals,  which  survive  the  immediate  effects  of  the  operation, 
subsequently  die  from  inanition,  almost  as  soon  as  if  they  had  been 
entirely  deprived  of  food. — The  observation  of  disease  in  the  human 
subject  leads  to  similar  conclusions ;  for,  when  the  biliary  secretion 
is  deficient,  or  its  flow  into  the  intestine  is  obstructed,  the  digestive 
processes  are  evidently  disordered ;  the  peristaltic  action  of  the  bowels 
is  not  duly  performed  ;  the  feces  are  white  and  clayey ;  and  there  is 
an  obvious  insufficiency  in  the  supply  of  nutriment  prepared  for  the 
absorbent  vessels. 

478.  On  the  other  hand,  that  one  great  object  of  the  secretion  is  to 
withdraw  from  the  blood  certain  products  of  the  decomposition  of  the 
tissues,  w^hich  would  otherwise  accumulate  in  it,  and  would  be  dele- 
terious to  its  character,  is  shown  by  evidence  yet  more  decisive.  We 
find  that  the  action  of  the  Liver  is  constant^  and  not  occasional,  like 
that  of  the  Salivary  and  Gastric  glands ;  and  that,  if  anything  inter- 


SECRETION  OF  BILE.  281 

fere  with  the  secreting  process,  and  thereby  cause  the  accumulation 
of  the  elements  of  the  bile  in  the  blood,  the  effects  of  their  presence 
are  immediately  manifested  in  the  disorder  of  other  functions,  espe- 
cially those  of  the  nervous  system  (§  399) ;  and  the  continued  suspen- 
sion of  the  function  leads  to  a  fatal  result,  unless  the  elements  of  the 
bile  are  drawn  off'  (as  sometimes  happens)  by  the  urinary  organs. 
When  the  secreting  action  of  the  liver  has  once  been  performed,  an 
obstruction  to  the  discharge  of  the  bile  into  the  intestine  does  not  seem 
to  be  so  immediately  injurious.  The  fluid  accumulates,  and  distends 
the  bile-ducts  and  the  gall-bladder ;  and  when  they  are  completely 
filled,  part  of  it  is  re-absorbed  into  the  blood,  apparently  in  a  changed 
condition,  since  it  does  not  then  produce  the  same  injurious  effects 
as  result  from  the  accumulation  of  the  same  materials,  previously  to 
the  action  of  the  Liver  upon  them.  The  colouring-matter  seems  to 
be  very  readily  taken  back  into  the  circulating  system;  and  is  depo- 
sited by  it  in  almost  every  tissue  of  the  body. 

479.  Although  the  secreting  action  of  the  Liver  is  constant,  yet 
the  discharge  of  bile  into  the  intestine  is  certainly  favoured  by  the 
presence  of  chyme  in  the  latter.  The  purpose  of  the  gall-bladder  is 
obviously  to  permit  the  accumulation  of  bile,  when  it  is  not  wanted 
in  the  intestine ;  and  we  find  it  most  constantly  present  in  those  tribes 
of  animals,  which  live  upon  animal  food,  and  which  therefore  take 
their  aliment  at  intervals ;  whilst  it  is  more  frequently  absent  in  those 
herbivorous  animals,  in  which  the  digestive  process  is  almost  con- 
stantly going  on.  The  middle  coat  of  the  bile-ducts  is  clearly  mus- 
cular, and  has  a  peristahic  action  like  that  of  the  intestinal  canal ;  this 
action  may  be  excited  by  galvanism,  or  by  irritation  of  the  branches 
of  the  Sympathetic  nerve,  by  which  it  is  supplied.  The  mucous  coat 
of  the  ductus  choledochus  is  disposed  in  valvular  folds,  in  such  a  man- 
ner as  to  prevent  the  reflux  of  the  bile  or  of  the  contents  of  the  intes- 
tine ;  and  a  still  further  security  is  afforded  by  the  valvular  covering 
to  the  orifice  of  the  duct,  which  is  furnished  by  the  mucous  covering 
of  the  intestine  itself.  The  flow  of  bile  into  the  intestine,  when  its 
presence  is  needed  there,  is  commonly  imputed  to  the  pressure  of  the 
distended  Duodenum  against  the  gall-bladder ;  but  it  is  probable  that 
the  contractility  of  the  muscular  coat  of  the  duct  itself,  which  may  be 
excited  either  through  the  sympathetic  nerve,  or  by  irritation  at  the 
orifice  of  the  duct  (as  in  the  case  of  the  Salivary  glands)  is  the  real 
cause  of  the  discharge  of  the  fluid.  It  is  an  interesting  fact,  which 
proves  how  much  the  passage  of  the  Bile  into  the  Intestine  is  depend- 
ent upon  the  presence  of  aliment  in  the  latter,  that  the  gall-bladder  is 
almost  invariably  found  turgid  in  persons  who  have  died  of  starvation; 
the  secretion  having  accumulated,  through  the  want  of  demand  for  it, 
although  there  was  no  obstacle  to  its  exit. 

480.  The  Pancreatic  secretion  appears  to  have  nearly  the  same 
qualities  as  Saliva  ;  the  proportion  of  solid  matter,  however,  being 
usually  greater.  Of  its  uses  in  the  digestive  process,  nothing  definite 
can  be  stated. 


282  SENSE  OF  HUNGER. 

481.  During  the  passage  of  the  contents  of  the  Intestine,  now  aug- 
mented by  the  biliary  secretion,  along  the  canal,  the  nutritious  portion 
is  gradually  withdrawn  by  the  absorbent  vessels  on  its  walls  ;  and  the 
excrementitious  matter  alone  remains.  This  is  increased  in  amount 
by  the  products  of  the  secretion  of  the  various  glandulse,  with  which 
the  mucous  lining  of  the  intestines  is  studded.  As  their  function, 
however,  is  obviously  to  get  rid  of  decomposing  matter  from  the  sys- 
tem, rather  than  to  contribute  in  any  way  to  the  preparation  of  the 
nutritive  materials,  it  will  be  more  properly  considered  hereafter 
(Chap.  XI).  Many  of  the  lower  animals  are  furnished,  at  the  part 
where  the  small  intestine  enters  the  large,  with  a  ccBcum,  resembling 
that  which  in  Man  is  termed  the  vermiform  appendage  of  the  csecum, 
but  greatly  exceeding  it  in  size.  Sometimes  we  find  two  caeca  in- 
stead of  one ;  and  these  are  much  prolonged,  so  as  to  form  tubes  of 
considerable  length.  It  has  been  ascertained  that,  in  herbivorous 
animals,  a  distinctly  acid  secretion  is  formed  by  the  caecum,  during 
the  digestive  process ;  and  there  is  reason  to  believe,  that  the  food 
there  undergoes  a  second  process,  analogous  to  that  to  which  it  has 
been  submitted  in  the  stomach,  and  fitted  to  extract  from  it  any  un- 
dissolved alimentary  matter  it  may  still  contain.  There  is  no  reason 
to  believe,  however,  that  any  such  process  takes  place  in  Man,  whose 
real  caecum  is  rudimentary, — the  part  of  the  intestine  which  has  re- 
ceived the  name,  being  merely  the  dilated  commencement  of  the 
colon.  The  act  of  defecation,  by  which  the  excrementitious  matter 
is  discharged,  has  been  already  noticed  (§  462);  the  Absorption  of 
nutritive  matter  will  be  treated  of  in  the  succeeding  Chapter. 

5.   Of  Hunger,  Satiety,  and  Thirst. 

482.  The  want  of  solid  aliment  is  indicated  by  the  sensation  of 
Hunger  ;  and  the  deficiency  of  fluid  by  that  of  Thirst.  On  the  other 
hand,  the  presence  of  a  sufficiency  of  food  or  liquid  in  the  stomach  is 
indicated  by  the  sense  of  Satiety.  These  sensations  are  intended  as 
our  guides,  in  regard  to  the  amount  of  aliment  we  take  in.  What  is 
the  real  seat  of  these  sensations,  and  on  what  conditions  do  they 
depend  ? 

483.  The  sense  of  Hunger  is  referred  to  the  stomach,  and  seems 
immediately  to  depend  upon  a  certain  condition  of  that  organ ;  but 
what  that  condition  is,  has  not  yet  been  precisely  ascertained.  It  is 
not  produced  by  mere  emptiness  of  the  stomach,  as  some  have  sup- 
posed ;  for,  if  the  previous  meal  have  been  sufficient,  the  food  passes 
entirely  from  the  cavity  of  the  stomach,  before  a  renewal  of  the  sensa- 
tion is  felt.  It  cannot  be  due  to  the  action  of  the  gastric  fluid  upon 
the  coats  of  the  stomach  themselves ;  because  this  fluid  is  not  poured 
into  the  stomach,  except  when  the  production  of  it  is  stimulated  by 
the  irritation  of  the  secreting  follicles.  It  has  been  attributed  to  dis- 
tension of  the  gastric  follicles  by  the  secreted  fluid  ;  but  there  is  no 
evidence  that  the  fluid  is  secreted  before  it  is  wanted  ;  and,  moreover, 


SENSE  OF  HUNGER  AND  SATIETY.  283 

it  is  well  known  that  mental  emotion  can  dissipate  in  a  moment  the 
keenest  appetite,  and  it  is  difficult  to  imagine  how  this  can  occasion 
the  emptying  of  the  follicles.  Perhaps  the  most  satisfactory  view  is 
that,  which  attributes  the  sense  of  hunger  to  a  determination  of  blood 
to  the  stomach,  preparing  it  for  the  secretion  of  gastric  fluid ;  since 
this  is  quite  adequate  to  account  for  the  impression  made  upon  the 
nerves;  and  it  accords  with  what  has  just  been  stated  of  the  influence 
of  mental  emotions,  since  we  know  that  these  have  a  powerful  effect 
upon  the  circulation  of  blood  in  the  minute  vessels  (§  603). 

484.  Although  the  sense  of  Hunger  is  immediately  dependent,  in 
great  part  at  least,  upon  the  condition  of  the  stomach,  yet  it  is  also 
indicative  of  the  condition  of  the  general  system ;  being  extremely 
strong,  when  the  body  has  undergone  an  unusual  waste  without  a  due 
supply  of  food,  even  though  the  stomach  be  in  a  state  of  distension ; 
whilst  it  is  not  experienced,  if,  through  the  general  inactivity  of  the 
system,  the  last  supply  has  not  been  exhausted,  even  though  the  sto- 
mach has  been  long  empty.  It  is  well  known,  that  when  food  is  defi- 
cient, the  attempt  to  allay  the  pangs  of  hunger  by  filling  the  stomach 
with  non-nutritious  substances,  is  only  temporarily  successful;  the 
feeling  soon  returning  wath  increased  violence,  though  it  has  received  a 
temporary  check.  The  reason  for  this  is  obviously,  that  the  general 
system  has  received  no  satisfaction,  although  the  stomach  has  been 
caused  to  secrete  gastric  fluid  by  the  contact  of  solid  matter  with  its 
walls,  so  that  the  state  on  which  hunger  immediately  depends,  has 
been  for  a  time  relieved.  This  state  is  soon  renewed,  unless  the  solid 
matter  introduced  into  the  stomach  be  of  an  alimentary  character,  and 
be  dissolved  and  carried  into  the  system. 

485.  When  the  food  is  nutritious  in  its  character,  but  of  small  bulk, 
experience  has  shown  the  advantage  of  mixing  it  with  non-nutritious 
substances,  in  order  to  give  it  bulk  and  solidity;  for  if  this  be  not 
done,  it  does  not  exert  its  due  stimulating  influence  upon  the  stomach  ; 
the  gastric  juice  is  not  poured  forth  in  proper  quantity ;  and  the  result 
is,  that  neither  is  the  sense  of  hunger  relieved,  nor  are  the  wants  of 
the  body  satisfied.  Thus  the  Kamschatdales  are  in  the  habit  of 
mixing  earth  or  saw-dust  with  the  train-oil,  on  which  alone  they  are 
frequently  reduced  to  live.  The  Veddahs  or  wild  hunters  of  Ceylon, 
on  the  same  principle,  mingle  the  pounded  fibres  of  soft  and  decayed 
wood  with  the  honey  on  which  they  feed  when  meat  is  not  to  be  had  ; 
and  on  one  of  them  being  asked  the  reason  of  the  practice,  he  replied, 
"  I  cannot  tell  you,  but  I  know  that  the  belly  must  be  filled."  It  has 
been  found  that  soups  and  fluid  diet  are  not  more  readily  converted 
into  chyme  than  solid  aliment,  and  are  not  alone  fit  for  the  support  of 
the  body  in  health ;  and  it  is  often  to  be  observed,  in  disordered  states 
of  the  stomach,  that  it  can  retain  a  small  quantity  of  easily-digested 
solid  food,  when  a  thin  broth  would  be  rejected. 

486.  The  sense  of  Satiety  is  the  opposite  of  Hunger ;  and  like  it, 
depends  on  two  sets  of  conditions, — the  state  of  the  stomach,  and  that 
of  the  general  system.     It  is  produced  in  the  first  instance  by  the 


284  HUNGER,  SATIETY,  AND  THIRST. 

ingestion  of  solid  matter  into  the  stomach,  which  gives  rise  to  the 
feeling  of  fullness  ;  but  this  is  only  a  part  of  the  sensation  which  ought 
to  be  experienced  ;  and  it  is  only  when  the  act  of  digestion  is  being 
duly  performed,  and  nutritive  matter  is  being  absorbed  into  the  ves- 
sels, that  the  peculiar  feeling  of  satisfaction  is  excited,  which  indicates 
that  the  wants  of  the  system  at  large  are  being  supplied. — It  has  been 
very  justly  remarked  by  Dr.  Beaumont,  that  the  cessation  of  the  de- 
mand set  up  by  the  system,  rather  than  the  positive  feeling  of  satiety, 
should  be  the  guide  in  regulating  the  quantity  of  food  taken  into  the 
stomach.  The  sense  of  satiety  is  beyond  the  point  of  healthful  indulg- 
ence ;  and  is  Nature's  earliest  indication  of  an  abuse  and  overburdening 
of  her  powers  to  replenish  the  system.  The  proper  intimation  is  the 
pleasurable  sensation  which  is  experienced,  when  the  cravings  of  the 
appetite  are  first  allayed  ;  since,  if  the  stomach  be  sufficiently  distended 
with  wholesome  food,  for  this  to  be  the  case,  it  is  next  to  certain  that 
the  digestion  of  that  food  will  supply  what  is  required  for  the  nutrition 
of  the  body.  It  is  only  when  the  substance  with  which  the  stomach 
is  distended,  is  not  of  a  digestible  character,  that  the  feelings  excited 
by  the  .state  of  that  organ  are  anything  but  a  correct  index  of  the 
wants  of  the  system. 

487.  The  Par  Vagum  is  evidently  the  nerve,  which  conveys  to  the 
sensorium  the  impression  of  the  state  of  the  stomachy  and  which  is 
therefore  the  immediate  excitor  of  the  sensation  of  hunger,  or  of  the 
feeling  of  satiety.  But  it  is  evident  from  experiments  upon  animals, 
that  it  is  not  the  only  source,  through  which  they  are  incited  to  take 
food,  and  are  informed  when  they  have  ingested  enough ;  and  it  is 
probable  that  the  Sympathetic  nerve  is  the  channel,  through  which 
the  wants  of  the  system  are  made  known,  and  through  which,  in 
particular,  the  feeling  of  general  exhaustion  is  excited,  that  is  expe- 
rienced when  there  has  been  an  unusual  waste,  or  when  the  proper 
supply  has  been  too  long  withheld. 

488.  The  conditions  of  the  sense  of  Thirst  are  very  analogous  to 
those  of  hunger;  that  is,  it  indicates  the  deficiency  of  fluid  in  the 
body  at  large  ;  but  the  immediate  seat  of  the  feeling  is  a  part  of  the 
alimentary  canal, — not  the  stomach,  however,  but  the  fauces.  It  is 
relieved  by  the  introduction  of  fluid  into  the  circulating  system, 
through  any  channel ;  whilst  the  mere  contact  of  fluids  with  the  sur- 
face to  which  the  sensation  is  referred,  produces  only  a  teniporary 
effect,  unless  absorption  take  place.  If  liquids  be  introduced  into  the 
stomach  by  an  oesophagus-tube,  they  are  just  as  effectual  in  allaying 
thirst,  as  if  they  w^ere  swallowed  in  the  ordinary  manner ;  and  the 
same  result  follows  the  injection  of  fluid  into  the  veins,  (as  was  most 
remarkably  the  case  when  this  method  of  treatment  was  practised  in 
the  Asiatic  Cholera,)  or  the  absorption  of  fluid  through  the  skin  or  the 
lower  part  of  the  alimentary  canal.  The  deficiency  of  fluid  in  the 
body  may  arise, — and  Thirst  may  consequently  be  induced, — either 
by  an  unusually  small  supply  of  fluid,  or  by  excessive  loss  of  the  fluids 
of  the  body,  as  by  perspiration,  diarrhoea,  &c.     But  it  may  also  be 


ABSORPTION  FROM  THE  DIGESTIVE  CAVITY.  285 

occasioned  by  the  impression  made  by  particular  kinds  of  food  or 
drink  upon  the  alimentary  canal ;  thus  salted  or  highly-spiced  meat, 
fermented  liquors  when  too  little  diluted,  and  other  similar  irritating 
agents,  excite  thirst ;  the  purpose  of  which  sensation  is  evidently  to 
cause  the  ingestion  of  fluid,  by  which  these  substances  may  be  diluted, 
and  their  irritating  action  prevented. 


I 


CHAPTER  V. 

ABSORPTION  AND  SANGUIFICATION. 

1.  Absorption  from  the  Digestive  Cavity. 

489.  So  long  as  the  Alimentary  matter  is  contained  in  the  digestive 
cavity,  it  is  as  far  from  being  conducive  to  the  nutrition  of  the  sys- 
tem, as  if  it  were  in  contact  with  the  external  surface.  It  is  only 
when  absorbed  into  the  vessels,  and  carried  by  the  circulating  current 
into  the  remote  portions  of  the  body,  that  it  really  becomes  useful  in 
maintaining  the  vigour  of  the  system,  by  replacing  that  which  has 
decayed,  and  by  affording  the  materials  for  the  various  organic  pro- 
cesses which  are  continually  going  on.  Among  the  Invertebrated 
animals,  we  find  the  reception  of  alimentary  matter  into  the  circula- 
ting system  to  be  entirely  accomplished  through  the  medium  of  the 
veinSy  which  are  distributed  upon  the  walls  of  the  digestive  cavity. 
We  not  unfrequently  observe,  that  the  intestinal  tube  is  completely 
enclosed  within  a  large  venous  sinus,  so  that  its  whole  external  sur- 
face is  bathed  with  blood  ;  and  into  this  sinus,  the  alimentary  mate- 
rials would  appear  to  transude,  through  the  walls  of  the  intestinal 
canal,  to  become  mingled  with  the  blood,  and  to  be  conveyed  with 
its  current  into  the  remote  portions  of  the  body.  Among  the  Verte- 
brata,  we  find  an  additional  set  of  vessels,  interposed  between  the 
w^alls  of  the  intestine  and  the  sanguiferous  system,  for  the  purpose, 
as  it  would  seem,  of  taking  up  that  portion  of  the  nutritive  matter 
which  is  not  in  a  state  of  perfect  solution,  and  of  preparing  it  for 
being  introduced  into  the  current  of  the  blood.  These  vessels  are  the 
ladeals  or  absorbents.  They  are  very  copiously  distributed  upon  the 
walls  of  the  small  intestine,  commencing  near  the  entrance  of  the 
biliary  and  pancreatic  ducts;  the  walls  of  the  large  intestine  are  less 
abundantly  supplied  with  them,  and  they  are  not  to  be  met  with  at  all 
on  the  walls  of  the  stomach. 

490.  Nevertheless  it  is  quite  certain,  that  substances  may  pass  into 
the  current  of  the  circulation,  which  have  been  prevented  from  pass- 
ing further  than  the  stomach ;  thus,  if  a  solution  of  Epsom-salts  be 
introduced  into  the  stomach  of  an  animal,  and  its  passage  into  the 


286  ABSORPTION  BY  ENDOSMOSE. 

intestine  be  prevented  by  a  ligature  around  the  pylorus,  its  purgative 
action  will  be  exerted  nearly  as  soon,  as  if  the  communication  between 
the  stomach  and  intestines  had  been  left  quite  free ;  or  if  a  solution 
of  prussiate  of  potash  be  introduced  into  the  stomach  under  similar 
circumstances,  the  presence  of  that  salt  in  the  blood  may  be  speedily 
demonstrated  by  chemical  tests. 

491.  This  passage  of  substances  in  a  state  of  perfect  solution,  from 
the  stomach  into  the  blood-vessels,  is  probably  due  to  the  operation 
of  that  peculiar  modification  of  Capillary  Attraction,  which  is  called 
Endosmose.  When  two  fluids  differing  in  density  are  separated  by  a 
thin  animal  or  vegetable  membrane,  there  is  a  tendency  to  mutual 
admixture  through  the  pores  of  the  membrane;  but  the  less  dense 
fluid  will  transude  with  much  greater  facility  than  the  more  dense  ; 
and  consequently  there  will  be  a  considerable  increase  on  the  side  of 
the  denser  fluid ;  whilst  very  little  of  this,  in  comparison,  will  have 
passed  towards  the  less  dense.  When  one  of  the  fluids  is  contained 
in  a  sac  or  cavity,  the  flow  of  the  other  towards  it  is  termed  Endos- 
ttiose,  or  flow-inwards ;  whilst  the  contrary  current  is  termed  Exos- 
mose  or  flow-outwards.  Thus  if  the  caecum  of  a  fowl,  filled  with 
syrup  or  gum-water,  be  tied  to  the  end  of  a  tube,  and  be  immersed 
in  pure  water,  the  latter  will  penetrate  the  caecum  by  Endosmose,  and 
will  so  increase  the  volume  of  its  contents,  as  to  cause  the  fluid  to 
rise  to  a  considerable  height  in  the  attached  tube.  On  the  other  hand, 
a  small  proportion  of  the  gum  or  syrup  will  find  its  way  into  the  sur- 
rounding fluid  by  Exosmose.  But  if  the  csecum  were  filled  with 
water,  and  were  immersed  in  a  solution  of  gum  or  sugar,  it  would  soon 
be  nearly  emptied, — the  Exosmose  being  much  stronger  than  the  En- 
dosmose. It  is  in  this  manner  that  we  may  cause  the  flattened  corpus- 
cles of  the  blood  to  be  distended  into  spheres,  by  treating  them  with 
water;  or  may  empty  them  almost  completely,  by  immersing  them  in 
syrup  (§  216);  since  their  contents  are  more  dense  than  the  surround- 
ing fluid  in  the  first  case,  so  that  they  will  be  augmented  by  Endos- 
mose ;  whilst  they  are  less  dense  in  the  second,  so  as  to  be  diminished 
by  Exosmose. 

492.  Now  it  seems  to  be  in  this  manner,  that  substances  contained 
in  the  cavity  of  the  stomach,  and  perfectly  dissolved  by  its  fluids,  are 
received  into  the  blood-vessels;  for  as  the  blood  is  the  fluid  of  greater 
density,  it  will  have  a  tendency  to  draw  towards  it,  by  Endosmose, 
the  saline  and  other  matters,  which  are  in  a  state  of  perfect  solution  in 
the  stomach.  The  mucous  membrane,  which  forms  the  inner  wall  of 
that  organ,  is  most  copiously  supplied  with  blood-vessels ;  partly, 
indeed,  that  they  may  afford  the  materials  of  the  gastric  secretion  ;  but 
partly,  also,  that  they  may  take  up  the  substances,  which  are  capable 
of  entering  the  circulating  current  by  this  direct  channel.  That  this 
act  of  absorption  is  principally  effected  by  the  veins  rather  than  by 
the  arteries,  appears  from  several  considerations.  The  walls  of  the 
former  are  much  thinner  than  those  of  the  latter.  Moreover,  the  for- 
mer are  usually  distributed  nearer  to  the  surface ;  whilst  the  latter  are 


ABSORPTION  OF  SOLUBLE  MATTERS  INTO  THE  VEINS.         287 

more  deeply-seated.  And  the  direction  of  the  passage  of  the  blood 
in  the  former  is  favourable  to  the  act  of  absorption,  whilst  in  the  latter 
it  is  the  reverse  ;  for  the  blood  in  the  arteries  is  passing  from  large 
trunks,  through  which  it  flows  with  facility,  into  the  innumerable  sub- 
divisions and  ramifications  of  the  capillary  system,  in  which  the  resist- 
ance to  its  flow  is  very  much  increased ;  whilst  in  the  veins,  the 
numerous  streams  flowing  through  the  capillaries  are  uniting  and  con- 
verging into  main  trunks  of  greatly-increased  capacity,  so  that  the 
resistance  is  greatly  diminished ;  and  it  is  easily  shown  on  Physical 
principles,  that  the  former  condition  presents  a  direct  obstacle  to 
absorption,  whilst  the  latter  as  directly  favours  it.  For  if  a  current 
of  fluid  be  made  to  pass  through  a  horizontal  tube,  which  undergoes 
an  enlargement  at  one  part  of  its  course,  so  that  the  fluid  passes  from 
the  smaller  to  the  larger  portion,  and  if  a  small  tube  be  made  to  open 
into  the  enlarged  part,  and  to  dip  down  vertically  into  a  basin  below, 
the  fluid  of  that  basin  will  be  caused  to  rise  in  the  small  tube,  so  as 
to  be  drawn  into  the  current  that  is  flowing  through  the  horizontal 
pipe, — and  this  with  a  force  proportional  to  the  amount  of  its  enlarge- 
ment, and  to  the  rapidity  of  the  current  that  is  flowing  through  it. 

493.  Although  it  is  difficult  to  speak  with  certainty  on  the  point, 
yet  there  appears  a  strong  probability  that,  both  in  the  stomach  and 
intestinal  tube,  the  absorption  of  nutritive  matters  in  a  state  of  per- 
fect solution^' — such  as  gum,  sugar,  pectine,  gelatin,  and  soluble 
albumen, — is  thus  accomplished  through 
the  medium  of  the  veins ;  which  also  Fig.  77. 
take  up  the  chief  supply  of  water  that  is 
required  by  the  system.  It  is  difficult 
else  to  see  the  purpose  of  the  extraordir 
nary  vascularity  of  the  mucous  mem- 
brane, and  in  particular  of  those  fila- 
ments or  narrow  folds,  termed  villi, 
which  so  thickly  cover  its  surface.  Each 
of  these  villi  is  furnished  with  a  plexus  ^.    .,    .       .  ^ 

«        .        ,        ,  ,         1  ,  ^         1  -1      .1  Distribution  of  Capillaries  in  the 

ot  minute   blood-vessels,  01    which  the        viiu  of  the  intestine. 
larger  branches  may  even  be  seen  with 

the  naked  eye,  when  they  are  distended  with  blood  or  with  a  coloured 
injection.  By  these  villi,  the  vascular  surface  of  the  mucous  mem- 
brane is  enormously  extended.  In  Man,  they  are  commonly  cylin- 
drical or  nearly  so,  and  are  from  about  a  quarter  of  a  line  to  a  line 
and  a  half  in  length ;  but  in  many  of  the  lower  animals  they  are 
spread  out  into  broader  laminae  at  the  base,  and  are  connected 
together  so  as  to  form  ridges  or  folds. — It  appears  from  the  experi- 
ments of  MM.  Tiedemann  and  Gmelin,  that  when  various  substances 
were  mingled  with  the  food,  which,  by  their  colour,  odour,  or  chemi- 
cal properties,  might  be  easily  detected, — such  as  gamboge,  madder, 
rhubarb,  camphor,  musk,  assafetida,  and  saline  compounds, — they 
were  seldom  found  in  the  chyle,  though  many  of  them  were  detected 
in  the  blood  and  in  the  urine.     The  colouring  matter  appeared  to  be 


288  ABSORPTION  INTO  THE  LACTEALS. 

seldom  absorbed  at  all ;  the  odorous  substances  were  generally  de- 
tected in  the  venous  blood  and  in  the  urine,  but  not  in  the  chyle; 
whilst,  of  the  saline  substances,  many  were  found  in  the  blood  and 
in  the  urine,  and  only  a  very  few  in  the  chyle. 

494.  Every  one  of  the  intestinal  Villi,  however,  also  contains  the 
commencement  of  a  proper  absorbent  vessel ;  and  this  system  of  ves- 
sels has  received  the  name  oi  lacteal^  on  account  of  the  milky  aspect 
of  the  fluid  which  is  found  within  it.  The  accompanying  figure 
represents  the  appearance  offered  by  the  incipient  lacteals  in  a  villus 
of  the  jejunum  of  a  young  man,  who  had  been  hung  soon  after  taking 

a  full  meal  of  farinaceous  food.  The  trunk  that 
^2^^^^  issues  from  the  villus  is  formed  by  the  conflu- 
ence of  several  smaller  branches,  whose  origin 
it  is  difficult  to  trace;  but  it  is  probable  that 
they  form  loops  by  anastomosis  with  each  other, 
so  that  there  is  no  proper  free  extremity  in  any 
case.  It  is  quite  certain  that  the  lacteals  never 
open  by  free  orifices  upon  the  surface  of  the 
intestine,  as  was  formerly  imagined.  From  the 
researches  of  Mr.  Goodsir,  already  referred  to, 
it  appears  that  these  loops  are  imbedded  in  a 
One  ofthe  intestinal  villi,     mass  of  cclls,  w^hich  are  the  real  agents  in  the 

•with  the  commencement  of  i       .•  r  xi.  i.      *    i      xi     i.  i      i*         i    ^ 

a  lacteal.  selcctiou  ot  the  materials  that  are  destined  to 

be  conveyed  into  the  lacteals;  and  that  the 
growth  of  these  cells  is  the  first  stage  of  the  process,  by  which  the 
nutritive  matters  that  are  in  a  state  of  very  fine  division^  but  not  in 
perfect  solution^  are  received  into  the  system  (§  241).  When  these 
cells  have  completed  their  ofldce,  and  have  passed  through  the  term 
of  their  lives,  they  yield  their  contents  to  the  absorbent  vessels,  either 
by  bursting  or  by  deliquescence;  and  thus  the  substances  whicl^i  they 
have  selected  and  combined  by  their  own  processes  of  growth,  are 
delivered  to  the  current  in  which  they  are  to  undergo  further  trans- 
formations, and  to  be  made  subservient  to  the  nutrition  of  the  general 
system. 

495.  It  is  particularly  important  to  keep  in  view  the  difference 
between  the  two  modes  by  which  alimentary  substances  are  intro- 
duced into  the  system,  when  we  are  treating  those  disordered  states 
in  which  the  digestive  process  is  imperfectly  performed,  or  altogether 
suspended.  There  can  be  little  doubt,  that  the  immediate  cause  of 
death,  in  many  diseases  of  exhaustion,  is  the  want  of  power  to  main- 
tain the  heat  of  the  body ;  the  stomach  not  being  able  to  dissolve 
food,  and  the  functions  of  the  lacteals  being  altogether  suspended, 
by  the  non-development  of  the  absorbing  cells,  so  that  the  inanition 
is  as  complete  as  if  food  were  altogether  withheld.  Now  under  such 
circumstances,  it  becomes  a  matter  of  greatest  importance  to  present 
a  supply  of  combustible  matter,  in  such  a  form  that  it  may  be  intro- 
duced into  the  circulating  system  by  simple  Endosmose ;  and  the 
value  which  experience  has  assigned  to  weak  broths  and  thin  fari- 


ABSORPTION  OF  ALCOHOL,  ETC.— MESENTERIC  GLANDS.       289 

naceoiis  solutions,  and  still  more,  to  diluted  alcoholic  drinks,  fre- 
quently repeated,  under  such  circumstances,  seems  to  depend  in 
great  part  upon  the  facility  with  which  they  may  be  thus  absorbed. 
The  good  effects  of  alcohol,  cautiously  administered,  are  no  doubt 
owing  in  part  to  its  specific  influence  upon  the  nervous  system  ;  but 
that  they  are  also  due  to  its  heat-producing  power,  appears  from 
the  results  of  the  administration  of  frequently-repeated  doses,  in 
states  of  utter  exhaustion, — the  temperature  of  the  body  being  kept 
up  so  long  as  they  are  continued,  and  falling  when  they  are  inter- 
mitted. As  the  alcohol  is  thus  burned  off",  nearly  as  fast  as  it  is 
introduced,  it  never  accumulates  in  sufficient  quantity  to  produce  its 
usual  violently-stimulating  effects  upon  the  nervous  system. 


2.  Passage  of  the  Chyle  along  the  Ladeals,  and  its  admixture  with  the 
Lymph  collected  from  the  general  System. 

496.  The  Lacteal  vessels,  which  commence  on  the  surface  of  the 
intestines,  run  together  on  their  walls,  and  form  larger  trunks,  which 
converge  and  unite  with  each  other  in  the  mesentery;  and  the  main 
trunks  thus  formed  then  enter  certain  bodies,  which  are  commonly 
known  as  the  **  mesenteric  glands."  Their  structure,  however,  does 
not  seem  to  correspond  with  that  of  the  proper  glands ;  as  they  are 


Fisr.  79. 


Fig.  80. 


Diagram  of  a  lymphatic  gland,  showing  the  in- 
tra-glandular  network,  and  the  transition  from 
the  scale-like  epithelia  of  the  extra-glandular 
lymphatics,  to  the  nucleated  cells  of  the  intra- 
glandular. 


Portion  of  intra-glandular  lymphatic,  showing 
along  the  lower  edge  the  thickness  of  the  germi- 
nal membrane,  and,  upon  it,  the  thick  layer  of 
glandular  epithelial  cells. 


simply  composed  of  lacteal  trunks,  convoluted  into  knots,  and  dilated 
into  larger  cavities,  amongst  which  blood-vessels  are  minutely  dis- 
tributed. These  blood-vessels  have  no  direct  communication  with 
the  interior  of  the  lacteals;  but  are  separated  from  them  by  the  mem- 
branous walls  of  both  sets  of  tubes.  The  epithelium,  which  lines  the 
absorbent  vessel,  undergoes  a  marked  change  where  the  vessel  enters 
the  gland,  and  becomes  more  like  that  of  the  proper  glandular  fol- 
licles in  its  character.  Instead  of  being  flat  and  scale-like,  and  form- 
ing a  single  layer  in  close  apposition  with  the  basement-membrane, 
as  it  does  in  the  lacteal  tubes  before  they  enter  the  gland  and  after 
they  have  emerged  from  it,  w^e  find  it  composed,  within  the  gland, 
of  numerous  layers  of  spherical  nucleated  cells  (Figs.  79  and  80); 
of  which  the  superficial  ones  are  easily  detached,  and  appear  to  be 
19 


290 


TERMINATION  OF  LACTEALS  IN  THORACIC  DUCT. 


Fig.  61. 


identical  with  the  cells  that  are  found  floating  in  the  chyle.     TJie 
purpose  of  these  cells  will  be  presently  inquired  into. 

497.  After  emerging  from 
the  mesenteric  glands,  the 
lacteal  trunks  converge,  with 
occasional  union,  until  they 
discharge  their  contents  into 
the  receptaculum  chyli,  which 
is  situated  at  the  front  of  the 
body  of  the  second  lumbar 
vertebra.  Into  the  same  cav- 
ity are  poured  the  contents 
of  a  part  of  the  other  division 
of  the  Absorbent  system; 
which  is  distributed  through 
the  body  in  general,  and 
which,  from  the  transparency 
of  the  fluid  or  lymph  it  con- 
tains, is  termed  the  lymphatic 
system.  From  the  recepta- 
culum chyli  arises  the  thora- 
cic duct;  which  passes  up- 
wards in  front  of  the  spine, 
receiving  other  lymphatic 
trunks  in  its  course,  to  ter- 
minate at  the  junction  of  the 
left  subclavian  and  jugular 
veins;  where  it  delivers  its 
contents  into  the  sanguiferous 
system.  A  smaller  duct  re- 
ceives some  of  the  lymphatics 
of  the  right  side,  and  there 
terminates  at  a  corresponding 
part  of  the  venous  system  ; 
but  it  does  not  receive  any 
of  the  contents  of  the  lac- 
teals. 

498.  The  lymphatic  sys- 
tem is  evidently  allied  very 
closely  to  the  lacteal,  in 
its  general  purposes ;  and 
makes  its  first  appearance 
in  the  same  class  of  ani- 
mals,   namely,     in     Fishes. 


The  course  and  termination  of  the  thoracic  duct.  1. 
The  arch  of  the  aorta.  2.  The  thoracic  aorta.  3.  The 
abdominal  aorta;  showing  its  principal  branches  di- 
vided near  their  origin.  4.  The  arteria  innominata,  di- 
viding into  the  right  carotid  and  right  subclavian  arteries. 
5.  Tlie  left  carotid.  6.  The  left  subclavian.  7.  The  su- 
perior cava,  formed  by  the  union  of,  8,  the  two  vinae  in- 
nominatae;  and  these  by  the  junction,  9,  of  the  internal 
jugular  and  subclavian  vein  at  each  side.  10.  The  greater 
vena  azygos  11.  The  termination  of  the  lesser  in  the 
greater  vena  azygos.  12.  The  receptaculum  chyli ;  seve- 
ral lymphatic  trunks  are  seen  opening  into  it.  13.  The  tho- 
racic duct,  dividing  opposite  the  middle  of  the  dorsal  ver- 
tebrae into  two  branches,  which  soon  reunite;  the  course 
of  the  duct  behind  the  arch  of  the  aorta  and  left  subclavian 
artery  is  shown  by  a  dotted  line.  14.  The  duct  making  its 
turn  at  the  root  of  the  neck,  and  receiving  several  lym- 
phatic trunks  previously  to  terminating  in  the  posterior 
aspect  of  the  junction  of  the  internal  jugular  and  subcla- 
vian vein.  15.  The  termination  of  the  trunk  of  the  ductus 
lymphaticus  dexter. 


The  vessels  of  which  it  is 
composed  are  distributed  through  most  of  the  softer  tissues  of  the 
body,  and  are  particularly  abundant  in  the  skin.  They  have  never 
been  found  to  commence  by  closed  or  open  extremities ;  but  seem  to 


LACTEAL  AND  LYMPHATIC  SYSTEMS.  291 

form  a  network,  from  which  the  trunks  arise.  In  their  course  they 
pass  through  glands,  disposed  in  different  parts  of  the  body,  which 
exactly  resemble  in  structure  those  which  are  found  upon  the  lacteals 
in  the  mesentery.  And  they  at  last  terminate,  as  already  shown,  in 
the  same  general  receptacle  with  the  lacteals.  Hence  it  cannot  be 
reasonably  doubted,  that  the  fluid  which  they  absorb  from  the  various 
tissues  of  the  body,  is  destined  to  become  again  subservient  to  nutri- 
tion ;  being  poured  back  into  the  current  of  the  blood,  along  with  the 
new  materials,  which  are  now  for  the  first  time  being  introduced  into 
it.  That  the  special  Absorbent  apparatus  of  Vertebrated  animals  has 
for  part  of  its  functions  to  effect  a  change  in  the  materials  absorbed, 
and  thus  to  aid  in  fitting  them  for  introduction  into  the  blood,  seems 
apparent  from  the  facts  of  Comparative  Anatomy  ;  which  show  that, 
the  more  distinct  the  blood  is  from  the  chyle  and  lymph,  the  more 
marked  is  the  provision  for  delaying  the  latter  in  the  absorbent  sys- 
tem, and  for  subjecting  it  to  preliminary  change. 

499.  The  course  of  the  lymphatic  and  lacteal  vessels  in  Fishes  is 
short  and  simple ;  they  are  not  furnished  with  glands  ;  and  they  pour 
their  contents  into  the  blood-vessels  at  several  different  parts  of  the 
body.  In  this  class  the  blood  contains  fewer  red  corpuscles,  and  its 
coagulating  power  is  feebler  than  in  any  other  Vertebrata.  And  in 
the  lowest  tribes,  in  which  the  Vertebrated  character  is  almost  entirely 
wanting,  and  in  which  the  blood  is  almost  pale,  no  special  absorbent 
system  has  yet  been  discovered.  In  Reptiles,  the  length  of  the  ab- 
sorbent vessels  is  remarkably  increased  by  their  doublings  and  convo- 
lutions ;  so  that  the  system  appears  to  be  more  highly  developed  than 
in  either  of  the  warm-blooded  classes.  But  this  superiority  is  not 
real ;  for  there  is  yet  no  trace  of  the  glands,  which  concentrate,  as  it 
were,  the  assimilating  power  of  a  long  series  of  vessels.  Moreover, 
we  often  find  the  lymphatics  of  this  class  furnished  with  pulsating  dila- 
tations, or  lymphatic  hearts ;  which  have  for  their  office  to  propel  the 
lymph  into  the  venous  system.  In  the  Frog  there  are  two  pairs  of 
these;  one  situated  just  beneath  the  skin  (through  which  its  pul- 
sations are  readily  seen  in  the  living  animal),  immediately  behind  the 
hip-joint ;  the  other  pair  being  more  deeply  seated  at  the  upper  part 
of  the  chest.  The  former  receive  the  lymph  of  the  posterior  part  of 
the  body,  and  pour  it  into  the  veins  proceeding  from  the  same  part ; 
the  latter  collect  that  which  is  transmitted  from  the  anterior  part  of 
the  body  and  head,  and  empty  their  contents  into  the  jugular  vein. 
Their  pulsations  are  totally  independent  of  the  action  of  the  heart, 
and  of  the  respiratory  movements ;  since  they  continue  after  the 
removal  of  the  former,  and  for  an  hour  or  two  subsequently  to  the 
death  and  complete  dismemberment  of  the  animal.  They  usually  take 
place  at  the  rate  of  about  sixty  in  the  minute  ;  but  they  are  by  no 
means  regular,  and  are  not  synchronous  on  the  two  sides. 

500.  In  Birds,  we  find  the  absorbent  system  existing  in  a  more 
perfect  form  ;  its  diffused  plexuses  and  convolutions  being  replaced 
by  glands ;  in  which  the  contained  fluid  is  brought  into  closer  proxi- 


^95i  ABSORPTION  BY  THE  LYMPHATICS. 

mity  with  the  blood  ;  and  in  which  it  is  subjected  to  the  influence  of 
assimilating  cells.  These,  however,  are  not  very  numerous  ;  being 
principally  found  on  the  lymphatics  of  the  upper  extremities.  The 
absorbents,  in  this  class,  terminate  principally  by  two  thoracic  ducts, 
one  on  each  side,  which  enter  the  jugular  veins  by  several  orifices. 
There  are,  however,  two  other  entrances,  as  in  Reptiles,  into  the 
veins  of  the  lower  extremity  ;  and  these  are  connected  with  two  large 
dilatations  of  the  lymphatics,  which  are  evidently  analogous  to  the 
lymphatic  hearts  of  Reptiles,  but  which  have  little  or  no  power  of 
spontaneous  contraction. — In  Mammalia,  the  absorbent  system  pre- 
sents itself  in  its  most  developed  and  concentrated  state.  The  vessels 
possess  firmer  walls,  and  are  more  copiously  provided  with  valves, 
than  in  the  classes  beneath;  and  the  glands  are  much  more  numerous, 
particularly  upon  the  vessels  that  receive  or  imbibe  substances  from 
without, — as  those  of  the  digestive  cavity,  the  skin,  and  the  lungs. 
The  terminations  of  the  absorbents  in  the  veins  are  usually  restricted, 
as  in  Man,  to  the  single  point  of  entrance  of  the  thoracic  duct  on 
either  side  ;  but  they  are  sometimes  more  numerous ;  and  certain 
variations  in  the  arrangement  of  the  thoracic  ducts,  which  occasion- 
ally present  themselves  as  irregularities  in  Man,  are  the  ordinary  con- 
ditions of  these  parts  in  some  of  the  lower  Mammalia. 

501.  With  regard  to  the  source  of  the  matters  absorbed  by  the 
lymphatics,  it  is  difficult  to  speak  with  certainty.  We  shall  presently 
see  that  their  contents  bear  a  close  resemblance  to  the  fluid  element 
of  the  blood,  or  "  liquor  sanguinis,"  in  a  state  of  dilution  ;  and  it  is 
very  probable  that  they  partly  consist  of  the  residual  fluid,  which, 
having  escaped  from  the  blood-vessels  into  the  tissues,  has  furnished 
the  latter  with  the  materials  of  their  nutrition,  and  is  now  to  be  re- 
turned to  the  former.  But  they  may  include,  also,  those  particles  of 
the  solid  frame-work,  which  have  lost  their  vital  powers,  and  which 
are  not  fit  therefore  to  be  retained  as  components  of  the  living  system, 
but  which  have  not  undergone  a  degree  of  decay  which  prevents 
them  from  serving,  like  matter  derived  from  the  dead  bodies  of  other 
animals,  as  a  material  for  reconstruction,  when  it  has  been  again  sub- 
jected to  the  organizing  process. 

502.  It  was  formerly  supposed  (and  the  doctrine  was  particularly 
inculcated  by  the  celebrated  John  Hunter),  that  the  office  of  the  Lym- 
phatic system  is  to  take  up  and  remove  all  the  effete  matter,  that  is 
to  be  cast  out  of  the  body,  being  no  longer  fit  for  its  nutrition.  But 
for  such  a  supposition  there  is  no  adequate  foundation.  It  seems 
absurd  to  imagine,  that  this  effete  matter  would  be  mingled  with  the 
newly-ingested  aliment,  and  would  be  poured  back  with  it  into  the 
general  current  of  the  circulation,  instead  of  being  at  once  carried 
out  of  the  system.  And  the  idea  is  directly  negatived,  as  we  shall 
presently  see,  by  the  actual  composition  of  the  lymph  drawn  from 
these  vessels  ;  the  solid  matter  of  which  consists,  in  great  part  at  least, 
of  substances  of  a  nutritive  character.  It  is  true  that  other  substances 
are  occasionally  found  in  the  lymphatics;  thus,  when  the  gall-bladder 


MOVEMENT  OF  FLUID  IN  ABSORBENTS.  293 

and  bile-ducts  are  over-distended  with  bile,  in  consequence  of  some 
obstruction  to  its  exit,  the  lymphatics  of  the  liver  are  found  to  contain 
a  biliary  fluid.  In  like  manner,  the  lymphatics  in  the  neighbourhood 
of  a  large  abscess  have  been  found  to  contain  pus.  When  the  limb 
of  an  animal,  round  the  upper  part  of  which  a  bandage  is  tied,  is  kept 
for  some  hours  in  tepid  milk,  the  lymphatics  of  the  skin  are  found 
distended  with  that  fluid.  And  when  saline  solutions  are  applied  to 
the  skin,  they  are  usually  detected  more  readily  in  the  lymphatics, 
than  in  the  veins.  But  these  facts  only  prove,  that  the  lymphatics 
very  readily  imbibe  soluble  substances  with  which  they  are  in  proxi- 
mity; and  this  imbibition  seems  to  take  place  on  the  same  physical 
principles,  as  the  imbibition  of  soluble  substances  by  the  veins  of  the 
intestinal  canal. 

503.  The  more  ready  absorption  of  such  substances  by  the  lympha- 
tics, than  by  the  veins,  of  the  cutaneous  surfaces, — contrary  to  what 
obtains  in  the  alimentary  canal, — is  easily  accounted  for,  by  the  very 
abundant  distribution  of  the  lymphatics  in  the  skin,  and  the  ready 
access  which  fluids  can  obtain  to  their  walls.  In  other  tissues  it  is 
different ;  thus  it  appears  that  saline  matters  injected  into  the  lungs 
are  detected  much  sooner  in  the  serum  of  the  blood  than  they  are  in 
the  lymph  ;  and  make  their  appearance  earlier  in  the  left  cavities  of 
the  heart,  to  which  they  would  be  conveyed  by  the  pulmonary  vein, 
than  in  the  right,  which  they  would  reach  through  the  thoracic  duct 
and  descending  cava.  This  is  obviously  due  to  the  minute  distribu- 
tion of  the  blood-vessels  upon  the  walls  of  the  air-cells;  which  makes 
them  far  more  ready  channels  for  the  imbibition  of  fluid,  than  the 
lymphatics  could  be. — In  regard  to  the  occasional  absorption  of  pus 
from  the  cavity  of  an  abscess  or  of  an  open  ulcer,  by  the  lymphatics, 
it  is  to  be  remarked  that  the  absorbent  vessels  must  themselves  pro- 
bably be  laid  open  by  ulceration  ;  since  in  no  other  way  can  we  un- 
derstand the  entrance  of  globules,  so  large  as  those  of  pus,  into  their 
interior. 

504.  In  regard  to  the  cause  of  the  movement  of  the  chyle  and 
lymph  along  the  absorbent  vessels,  from  their  commencement  to  their 
termination  in  the  central  receptacle,  no  very  definite  account  can  be 
given.  The  middle  coat  of  these  vessels  has  a  fibrous  texture  ;  and 
the  fibres  bear  some  resemblance  to  that  of  the  non-striated  muscle. 
In  the  thoracic  duct,  this  fibrous  structure  is  more  evident ;  and  dis- 
tinct contractions  have  been  excited  in  it,  by  irritating  the  sympathe- 
tic trunks  from  which  it  receives  its  nerves,  and  the  roots  of  the  spinal 
nerves  with  which  those  trunks  are  connected.  Hence  it  seems  pro- 
bable, that  there  is  a  sort  of  peristaltic  contraction  of  the  walls  of  the 
absorbents,  analogous  to  that  which  takes  place  in  the  intestinal  tube, 
serving  to  drive  their  contents  slowly  onwards ;  their  reflux  being 
prevented  by  the  valves,  with  which  they  are  copiously  furnished. 
Moreover,  it  is  probable  that  the  general  movements  of  the  body  may 
concur  with  the  contractile  power  of  the  absorbent  vessels  themselves, 
to  urge  their  contents  onwards  ;  for  almost  every  change  in  position 


2^  STRUCTURE  AND  FUNCTIONS  OF  THE  SPLEEN. 

must  occasion  increased  pressure  on  some  portion  of  them,  which  will 
propel  the  fluid  contents  in  the  sole  direction  permitted  by  the  valves, 
and  thus  give  them  an  additional  impulse  towards  the  trunks,  in  which 
they  are  collected  for  delivery  into  the  blood-vessels. 

3.   Of  the  Spleen^  and  other  Glandular  Appendages  to  the  Lymphatic 

System. 

505.  The  structure  and  functions  of  the  Spleen,  and  of  certain 
other  organs  allied  to  it  in  character,  have  been  among  the  most 
obscure  subjects  in  Anatomy  and  Physiology;  and  they  are  far  from 
having  been  yet  fully  elucidated.  There  seems  sufficient  evidence, 
however,  for  regarding  them  in  the  light  of  appendages  to  the  Lym- 
phatic system,  and  as  concerned,  like  it,  in  the  process  of  Sanguifica- 
tion, or  the  preparation  of  Blood.  Hence  this  appears  to  be  the  most 
appropriate  place,  for  such  a  brief  notice  of  them,  as  the  present  state 
of  our  knowledge  admits. 

506.  The  Spleen  is  certainly  to  be  regarded  as  an  organ  of  com- 
pound structure,  having  at  least  two  sets  of  functions  to  fulfil.  It  is 
essentially  composed  of  a  fibrous  membrane,  which  constitutes  its 
exterior  envelop,  and  which  sends  prolongations  in  all  directions 
across  its  interior,  so  as  to  divide  it  into  a  number  of  minute  cavities 
or  follicles  of  irregular  form.  These  splenic  follicles  communicate 
freely  with  each  other,  and  with  the  splenic  vein,  and  they  are  lined 
by  a  continuation  of  the  lining  membrane  of  the  latter.  The  partitions 
between  the  follicles  are  formed,  not  only  by  these  membranes,  but 
by  the  peculiar  parenchyma  of  the  Spleen  ;  and  this  seems  to  be  made 
up  of  reticulations  of  blood-vessels  and  lymphatics,  with  a  large 
quantity  of  minute  globules  or  incipient  cells,  of  about  half  the  dia- 
meter of  blood-corpuscles,  which  lie  in  the  meshes  of  the  capillary 
network,  and  which  seem  to  be  in  intimate  connection  with  the  lym- 
phatics. Lying  in  the  midst  of  this  parenchyma,  there  are  found  a 
large  number  of  bodies,  about  one-third  of  a  line  in  diameter,  which 
are  known  as  the  Malpighian  bodies  of  the  Spleen.  These  resemble 
lymphatic  glands  in  miniature,  being  composed  of  convoluted  masses 
of  blood-vessels  and  lymphatics,  united  by  elastic  tissue  ;  and  the 
lymph  they  contain  is  rendered  somewhat  milky  by  the  large  number 
of  the  lymph-corpuscles  that  float  in  them,  although  the  fluid  of  the 
afferent  lymphatics  is  quite  clear; — so  that  the  correspondence  both 
in  structure  and  function  seems  to  be  exact. 

507.  The  parenchymatous  and  the  cellated  structures  do  not  seem  to 
bear  any  constant  proportion  to  each  other;  thus  the  former  prevails 
most  in  Man,  and  the  latter  in  the  Herbivora.  The  walls  of  the  fol- 
licles are  so  elastic,  that  their  cavities  may  be  greatly  distended  with 
a  very  moderate  force, — the  Spleen  of  the  sheep,  which  weighs  about 
4  oz.,  being  easily  made  to  contain  about  30  oz.  of  water.  This  pecu- 
liar distensibility  evidently  points  to  the  Spleen  as  a  kind  of  reser- 
voir, connected  with  the  Portal  circulation,  for  the  purpose  of  reliev- 


STRUCTURE  AND  FUNCTIONS  OF  THE  SPLEEN.  295 

ing  the  portal  vessels  from  undue  pressure  or  distension,  under  a  great 
variety  of  circumstances.  The  portal  system  is  well  known  to  be 
destitute  of  valves,  so  that  the  splenic  vein  communicates  freely  with 
the  whole  of  it;  and  thus,  if  any  obstruction  exist  to  the  flow  of 
blood  through  the  liver,  or  any  peculiar  pressure  elsewhere  prevents 
the  mesenteric  veins  from  dilating  to,  their  full  extent,  the  general  cir- 
culation is  not  disturbed, — the  Spleen  affording  a  kind  of  safety-valve. 
That  any  cause  of  congestion  of  the  Portal  system  peculiarly  affects 
the  Spleen,  has  been  proved  by  experiment ;  for,  after  the  portal  vein 
has  been  tied,  the  spleen  of  an  animal  that  previously  weighed  only 
2  oz.,  has  been  found  to  increase  20  oz.  Further,  in  Asphyxia, 
when  the  circulation  of  blood  is  checked  in  the  Lungs,  and  when  the 
stagnation  extends  itself  backwards  to  the  right  side  of  the  heart,  to 
the  vena  cava,  and  thence  to  the  portal  system,  the  Spleen  is  often 
found  after  death  to  be  enormously  distended  with  blood.  And  in 
the  cold  stage  of  intermittent  fever,  in  which  a  great  quantity  of  blood 
is  driven  from  the  surface  towards  the  internal  organs,  the  Spleen 
receives  a  large  portion  of  it,  so  that  its  increased  size  becomes  quite 
perceptible ;  and  in  cases  of  confirmed  Ague,  the  Spleen  becomes 
permanently  enlarged,  forming  what  is  popularly  known  as  the  **  ague- 
cake." — Again,  the  Spleen  appears  to  serve  as  a  reservoir,  into  which 
superfluous  blood  may  be  carried,  during  the  digestive  process. 
When  the  alimentary  canal  is  distended  with  food,  and  a  great  afflux 
of  arterial  blood  takes  place  to  the  mucous  membrane,  the  veins  of 
the  portal  system  will  be  liable  to  increased  pressure  from  without, 
whilst  their  contents  will  be  augmented  by  the  quantity  of  fluid  newly 
absorbed  from  the  alimentary  canal.  In  this,  as  in  the  preceding 
cases,  the  distensibility  of  the  spleen  makes  it  a  kind  of  safety-valve, 
by  which  undue  distension  of  the  portal  system  is  relieved.  It  has 
been  ascertained  that  its  maximum  volume  is  attained  about  five  hours 
after  a  meal,  when  the  process  of  chymiiication  is  at  an  end,  and  that 
of  absorption  is  taking  place  with  activity  ;  and  the  increase  is  pro- 
portional rather  to  the  amount  of  the  fluids  ingested,  than  to  that  of 
the  solids. 

508.  But  besides  this  safety-valve  function,  there  can  be  little  ques- 
tion that  the  Spleen  performs  another,  which  corresponds  with  the 
function  of  the  lymphatic  glands  in  general.  The  identity  in  struc- 
ture between  its  Malpighian  bodies,  and  the  ordinary  lymphatic  glands, 
is  such  as  clearly  points  to  this  inference ;  and  it  is  confirmed  by  this 
remarkable  fact,  which  has  been  ascertained  by  recent  experiments, — 
that  after  the  spleen  has  been  extirpated,  the  lymphatic  glands  of  the 
neighbourhood  increase  in  size,  and  cluster  together  as  they  enlarge, 
so  as  to  form  an  organ  that  at  least  equals  the  original  spleen  in  volume. 
This  circumstance  explains  the  reason  of  the  almost  invariable  negative 
result  of  the  extirpation  of  the  spleen;  for  although  the  operation  has 
been  frequently  practised,  with  the  view  of  determining  the  functions 
of  the  organ  by  the  symptoms  presented  by  the  animals  after  its  re- 


29$.  SUPRA-RENAL  CAPSULES. 

moval,  no  decided  change  in  the  ordinary  course  of  their  vital  pheno- 
mena has  ever  been  observed,  and  the  health,  if  at  all  disturbed  for 
a  time,  is  afterwards  completely  regained.  Now  if  the  functions  of 
the  Spleen, — putting  aside  the  safety-valve  action  of  its  distensible' 
cavities, — be  the  same  with  that  of  the  lymphatic  glands  in  general, 
it  is  easy  to^  understand  how  its  loss  may  be  at  once  compensated  by 
an  increased  action  on  their  part,  and  how  it  may  be  permanently 
replaced  by  an  increased  development  of  certain  of  those  bodies. — 
Thus,  then,  we  may  fairly  regard  the  Spleen  as  concurring  with  the 
glands  of  the  absorbent  system,  in  the  assimilating  process,  by  which 
the  crude  nutritive  materials  are  rendered  fit  to  circulate  in  the  blood; 
and  as  the  latter  operate  upon  those  which  are  taken  up  by  the  lac- 
teals,  so  may  the  former  exert  their  influence  upon  those,  which  have 
been  received  into  the  veins, — separating  them  from  the  mass  of  the 
blood,  and  delivering  them  to  the  lymphatics  to  be  further  elabo- 
rated. 

509.  It  is  worthy  of  remark,  that  a  Spleen  is  found  in  all  Verte- 
brated  animals,  which  have  a  distinct  Absorbent  system ;  but  that  no 
organ  exactly  corresponding  with  it  exists  in  the  Invertebrata,  which 
are  destitute  of  that  system, — although  the  distensible  cellated  cavi- 
ties, apparently  destined  to  perform  its  safety-valve  function,  exist  in 
some  of  the  higher  among  them.  This  is  an  additional  reason  for 
regarding  its  parenchymatous  portion  as  essentially  a  part  of  the  assi- 
milating apparatus  of  the  Absorbent  system. 

510.  The  Supra-Re7ial  Capsules  seem  to  correspond  with  the  Spleen 
in  their  general  structure,  and  in  their  connection  with  the  Lymphatic 
system  ;  whilst  in  the  arrangement  of  their  component  parts,  they  bear 
more  resemblance  to  the  Kidney.  Their  exterior  or  cortical  portion  is 
formed  of  straight  arteries,  which  divide  into  a  minute  capillary  net- 
work ;  and  from  this  arise  venous  branches,  which  form  a  minute 
plexus,  pouring  its  contents  into  a  large  central  cavity,  which  is  the 
dilafed  commencement  of  the  supra-renal  vein.  No  apparatus  of 
secreting  tubes  or  vesicles  can  be  detected  in  it ;  but  the  interspaces 
of  the  venous  plexus  are  filled  up  with  a  sort  of  pulp  consisting  of 
minute  spherules,  averaging  about  l-10,000th  of  an  inch  in  diameter, 
but  varying  from  nearly  twice  that  size  to  less  than  half.  These 
bodies  appear  to  be  the  nuclei  of  cells,  the  full  development  of  which 
is  checked  ;  but  in  the  Ruminant  animals,  and  occasionally  in  the 
Human  subject,  the  cells  are  more  or  less  developed,  and  then  re- 
semble the  ordinary  lymph-corpuscles  in  size  and  appearance.  The 
Lymphatics  are  of  large  size,  like  those  of  the  Spleen  ;  and  probably 
convey  away  the  matter  which  has  been  elaborated  by  these  organs, 
that  it  may  be  mingled  with  that  which  is  being  taken  up  and  pre- 
pared by  other  parts  of  the  Absorbent  system.  The  Supra-Renal 
capsules  attain  a  very  large  size  early  in  foetal  life,  surpassing  the  true 
Kidneys  in  dimension,  up  to  the  tenth  or  twelfth  week;  but  they 
afterwards  diminish  relatively  to  the  latter,  and  are  evidently  subor- 


THYMUS  GLAND.  297 

dinate  organs,  during  the  whole  remainder  of  life.  It  does  not  seem 
unlikely  that  these  bodies,  like  the  Spleen,  have  a  double  function ; 
and  that,  besides  participating  in  the  general  actions  of  the  Absorb- 
ent glandulse,  they  may  serve  as  a  diverticulum  for  the  Renal  circu- 
lation, when  from  any  cause  the  secreting  function  of  the  Kidneys  is 
retarded  or  checked,  and  the  movement  of  blood  through  them  is 
stagnated. 

511.  The  Thymus  Gland  is  another  body,  which  seems  referable 
to  the  same  group ;  having  all  the  essential  characters  of  a  true  gland 
(§  714),  save  an  excretory  duct ;  and  its  function  being  evidently 
connected,  during  the  early  period  of  life  at  least,  with  the  elaboration 
of  nutritive  matter,  which  is  to  be  re-introduced  into  the  circulating 
current.  Its  elementary  structure  may  be  best  understood  from  the" 
simple  form  it  presents,  when  it  is  first  capable  of  being  distinguished 
in  the  embryo.  It  then  consists  of  a  single  tube,  closed  at  both  ends, 
and  filled  with  granular  matter;  and  its  subsequent  development  con- 
sists in  the  lateral  growth  of  branching  off-shoots  from  this  central 
tubular  axis.  In  its  mature  state,  therefore,  it  consists  of  an  assem- 
blage of  glandular  follicles,  which  are  surrounded  by  a  plexus  of 
blood-vessels ;  and  these  follicles  all  communicate  with  the  central 
reservoir,  from  which,  however,  there  is  no  outlet.  The  cavities  of 
the  follicles  contain  a  fluid,  in  which  a  number  of  corpuscles  are 
found,  giving  it  a  granular  appearance.  These  corpuscles  are  for  the 
most  part  in  the  condition  of  nuclei;  but  fully  developed  cells  are 
found  among  them,  at  the  period  when  the  function  of  this  body 
seems  most  active. "  The  chemical  nature  of  the  contents  at  this 
period,  closely  resembles  that  of  the  ordinary  proteine-compounds. — 
It  has  been  commonly  stated,  that  the  Thymus  attains  its  greatest 
development,  in  relation  to  the  rest  of  the  body,  during  the  latter 
part  of  fcetal  life ;  and  it  has  been  considered  as  an  organ  peculiarly 
connected  with  the  embryonic  condition.  But  this  is  a  mistake  ;  for 
the  greatest  activity  in  the  growth  of  this  organ  manifests  itself,  in  the 
Human  infant,  soon  after  birth ;  and  it  is  then,  too,  that  its  functional 
energy  seems  the  greatest.  This  rapid  state  of  growth,  however,  soon 
subsides  into  one  of  less  activity,  which  merely  serves  to  keep  up  its 
proportion  to  the  rest  of  the  body  ;  and  its  increase  usually  ceases 
altogether  at  the  age  of  about  two  years.  From  that  time,  during  a 
variable  number  of  years,  it  remains  stationary  in  point  of  size ;  but, 
if  the  individual  be  adequately  nourished,  it  gradually  assumes  the 
character  of  a  mass  of  fat,  by  the  development  of  the  corpuscles  of  its 
interior  into  fat-cells,  which  secrete  adipose  matter  from  the  blood. 
This  change  in  its  function  is  most  remarkable  in  hybernating  Mam- 
mals; in  which  the  development  of  the  organ  continues,  even  in  an 
increasing  ratio,  until  the  animal  reaches  adult  age,  when  it  includes 
a  large  quantity  of  fatty  matter.  The  same  is  the  case,  generally 
speaking,  among  Reptiles.  It  is  an  important  fact  in  the  history  of 
this  organ,  that  it  is  not  to  be  detected  in  Fishes ;  and  does  not  appear 
to  exist,  either  in  the  tadpole  state  of  the  Batrachian  reptiles,  or  in  the 


298  THYMUS  GLAND.— THYROID  GLAND. 

Perennibranchiate  group ;  so  that  we  may  regard  it  as  essentially  con- 
nected with  pulmonic  respiration.* 

512.  Various  facts  lead  to  the  conclusion,  that  the  function  of  the 
Thymus,  at  the  period  of  its  highest  development,  is  that  of  elabo- 
rating and  storing  up  nutritive  materials,  to  supply  the  demand  which 
is  peculiarly  active  during  the  early  period  of  extra-uterine  life.  The 
elaborating  action  probably  corresponds  with  that,  which  is  exerted 
by  the  glands  of  the  Absorbent  system ;  and  the  product,  as  in  the 
preceding  cases,  seems  to  be  conveyed  away  by  the  lymphatics.  The 
provision  of  a  store  of  nutritive  matter  seems  a  most  valuable  one, 
under  the  circumstances  in  which  it  is  met  with ;  the  waste  being 
more  rapid  and  variable  than  in  adults,  and  the  supply  not  constant. 
Thus  it  has  been  noticed  that,  in  over-driven  lambs,  the  thymus  soon 
shrinks  remarkably;  but  that  it  becomes  as  quickly  distended  again 
during  rest  and  plentiful  nourishment.  As  the  demand  becomes  less 
energetic,  and  as  the  supplies  furnished  by  other  organs  become  more 
adequate  to  meet  it,  the  Thymus  diminishes  in  size,  and  no  longer 
performs  the  same  function.  It  then  obviously  serves  to  provide  a 
store  of  material,  not  for  the  nutrition  of  the  body,  but  for  the  respi- 
ratory process,  when  this  has  to  be  carried  on  for  long  periods — as  in 
hybernating  Mammals  and  in  Reptiles — without  a  fresh  supply  of 
food. — It  is  possible  that  the  Thymus  gland  may  further  stand  in  the 
same  relation  to  the  Lungs,  as  the  Spleen  to  the  Liver,  and  the  Supra- 
Renal  capsules  to  the  Kidneys ;  that  is,  as  a  diverticulum  for  the 
blood  transmitted  through  the  bronchial  arteries  (which  are  the 
nutritive  vessels  of  the  Lungs),  before  the  Lungs  acquire  their  full 
development  in  comparison  with  other  organs,  or  when  any  cause 
subsequently  obstructs  the  circulation  through  their  capillaries. 

513.  The  Thyroid  Gland  bears  a  general  analogy  to  the  Thymus; 
but  its  vesicles  are  distinct  from  each  other,  and  do  not  communicate 
with  any  common  reservoir.  They  are  surrounded,  like  the  vesicles 
of  the  true  glands,  with  a  minute  capillary  plexus ;  and  in  the  fluid 
they  contain,  numerous  corpuscles  are  found  suspended,  which  appear 
to  be  cell-nuclei,  in  a  state  of  more  or  less  advanced  development. 
This  body  is  supplied  with  arteries  of  considerable  size ;  and  with 
peculiarly  large  lymphatics.  Though  proportionably  larger  in  the 
foetus  than  in  the  adult,  it  remains  of  considerable  size  during  the 
whole  of  life.  It  appears,  from  the  recent  inquiries  of  Mr.  Simon, f 
that  a  Thyroid  gland,  or  some  organ  representing  it  in  place  and 
office,  exists  in  all  Vertebrated  animals.  It  presents  its  simplest  form 
in  the  class  of  Fishes;  in  some  of  which  it  appears  to  consist  merely 
of  a  plexus  of  capillary  vessels,  connected  with  the  origin  of  the 
cerebral  vessels,  and  capable,  by  its  distensibility,  of  relieving  the 
latter,  in  case  of  any  obstruction  to  the  proper  movement  of  blood 
through  them.  In  the  higher  forms  of  this  organ,  the  glandular 
structure, — consisting  of  the  closed  vesicles  over  which  the  capillary 

*  See  Mr.  Simon's  admirable  Prize  Essay  on  the  Thymus  Gland. 
I  Philosophical  Transactions,  1844. 


CHARACTERS  OF  CHYLE  AND  LYMPH.  299 

plexus  is  distributed,  and  of  their  cellular  contents, — is  superadded  : 
and  the  organ  then  appears,  like  the  Spleen,  to  be  destined  for  two 
different  uses  ;  namely,  to  serve  as  a  diverticulum  to  the  Cerebral 
circulation;  and  to  aid  in  the  elaboration  of  nutritive  matter,  which  is 
taken  up  by  the  Absorbent  system,  and  which  is  again  poured  by  it 
into  the  general  current  of  the  circulation. 

514.  Thus  the  Spleen,  the  Supra-Renal  Capsules,  the  Thymus 
Gland,  and  the  Thyroid  Gland,  all  seem  to  share  in  the  preparation 
of  the  nutritive  materials  of  the  blood,  along  with  the  ordinary  glan- 
dulee  of  the  Absorbent  system.  In  fact,  we  may  regard  them  all  as 
together  constituting  an  apparatus,  which  is  precisely  analogous  to 
that  of  the  ordinary  glands,  but  of  which  the  elementary  parts  are 
scattered  through  the  body,  instead  of  being  collected  into  one  com- 
pact structure.  Thus  if  we  could  imagine  any  tubular  gland,  such 
as  the  Kidney  or  the  Testis,  to  be  unraveled,  and  its  convoluted 
tubuli  to  be  spread  through  the  system,  yet  all  discharging  their  con- 
tents by  a  common  outlet,  we  should  have  no  unapt  representation  of 
the  Lymphatic  portion  of  the  Absorbent  system.  Its  function  appears 
to  be,  to  separate  the  crude  Albuminous  matter  from  the  blood,  to 
subject  it  to  an  elaborating  action  performed  by  the  epithelium-cells 
lining  the  tubes,  and  then  to  pour  forth  this  elaborated  product, — not 
as  an  excretion  to  be  carried  out  of  the  body, — but  (in  conjunction 
with  that,  w^hich  has  been  newly  taken  in  by  the  Lacteal  portion  of  the 
system,  and  which  has  undergone  elaboration  by  its  glandulse),  into 
the  blood-vessels,  which  are  to  convey  it  to  the  different  parts  of  the 
body  where  it  is  to  be  appropriated.  The  four  bodies  we  have  been 
just  considering,  appear  to  be,  so  far  as  their  glandular  function  is 
concerned,  appendages  to  this  system.  Their  uses  as  diverticula  to 
the  circulation  through  other  organs,  render  them  liable  to  occasional 
distension  with  blood ;  and  it  seems  determined  that  this  blood  shall 
not  lie  useless,  but  shall  be  subservient  to  the  action  in  question ;  the 
gland-cells  that  line  the  cavities  of  the  organ  withdrawing  certain 
constituents  of  the  blood,  to  restore  them,  through  the  Lymphatic 
system,  in  a  state  of  more  complete  preparation  for  the  operations  of 
Nutrition.  Their  function  is  very  probably  vicarious ;  that  is,  the 
determination  of  blood  is  greatest  (through  the  state  of  the  other 
organs)  at  one  time  to  one  of  these  bodies,  and  at  another  time  to 
another.  Hence  the  effects  of  the  loss  of  any  one  of  them  are  not 
serious  ;  as  the  others  are  enabled  in  great  degree  to  discharge  its 
duty. 

4.   Composition  and  properties  of  the  Chyle  and  Lymph. 

515.  The  chief  chemical  difference  between  the  Chyle  and  the 
Lymph,  consists  in  the  much  smaller  proportion  of  solid  matter  in  the 
latter,  and  in  the  almost  entire  absence  of  fat,  which  is  an  important 
constituentof  the  former.  This  is  well  shown  in  the  following  com- 
parative analyses,  performed  by  Dr.  G.  0.  Rees,  of  the  fluids  obtained 


30Q 


CHARACTERS  OF  CHYLE  AND  LYMPH. 


from  the  lacteal  and  lymphatic  vessels  of  a  donkey,  previously  to  their 
entrance  into  the  thoracic  duct ;  the  animal  having  had  a  full  meal 
seven  hours  before  its  death. 


Water  -  -  -  . 

Albuminous  matter  (coagulable  by  heat) 
Fibrinous  matter  (spontaneously  coagulable) 
Animal  extractive  matter,  soluble  in  water 

and  alcohol 
Animal  extractive  matter,  soluble  in  water 

only  ...  - 

Fatty  matter         -  -  - 

Salts  ; — Alkaline  chloride,  sulphate  and  car- 
bonate, with  traces  of  alkaline  phosphate, 
oxide  of  iron  -  -  _ 


Chyle.  Lymph. 

90-237  95-536 

3-516  1-200 

0-370  0-120 

0-332  0-240 

1'233  1-319 

3-601  a  trace. 


0-711     0-585 


100-000       100-000 

The  Lymph  obtained  from  the  neck  of  a  horse  has  been  recently 
analyzed  by  Nasse,  with  nearly  the  same  result.  He  found  it  to  con- 
tain 95  per  cent,  of  water ;  and  the  5  per  cent,  of  solid  matter  was 
chiefly  composed  of  albumen  and  fibrin,  with  watery  extractive, — 
scarcely  a  trace  of  fat  being  to  be  found.  The  proportions  of  saline 
matter  were  found  to  be  remarkably  coincident  with  those,  which  exist 
in  the  serum  of  the  blood  ;  as  might  be  expected  from  the  fact,  that 
the  fluid  portion  of  the  lymph  must  have  its  origin  in  that  which  has 
transuded  through  the  blood-vessels:  the  absolute  quantity,  however, 
is  rather  less. — A  similar  analysis  of  the  Chyle  of  a  cat  by  Nasse,  has 
given  results  very  closely  correspondent  with  that  of  Dr.  Rees  ;  for 
the  proportion  of  water  was  90-5  per  cent.  ;  and  of  the  9-5  parts  of 
solid  matter,  the  albumen,  fibrin,  and  extractive  amounted  to  more 
than  5,  and  the  fat  to  more  than  3  parts. — Dr.  Rees  has  also  analyzed 
the  fluid  of  the  Thoracic  duct  of  Man ;  which  consists  of  chyle  with 
an  admixture  of  lymph  ;  and  he  found  this  to  contain  about  90-5  per 
cent,  of  water,  7  parts  of  albumen  and  fibrin,  1  part  of  aqueous 
alcoholic  extractive,  and  not  quite  1  part  of  fatty  matter  with  about  J 
per  cent,  of  salines.  The  composition  of  this  fluid  more  resembles 
that  of  the  lymph  than  that  of  the  chyle ;  the  proportion  of  the  fatty 
to  the  albuminous  matter  being  small.  This  was  probably  due  to  the 
circumstance,  that  the  subject  from  which  it  was  obtained  (an  executed 
criminal)  had  eaten  but  little  for  some  hours  before  his  death. 

516.  The  characters  of  the  Chyle  are  not  the  same  in  every  part  of 
the  Lacteal  system;  for  the  fluid  undergoes  a  very  important  series  of 
changes  in  its  characters,  in  its  transit  from  the  walls  of  the  intestines 
to  the  receptaculum  chyli.  The  fluid  drawn  from  the  lacteals  that 
traverse  the  intestinal  walls,  has  no  power  of  spontaneous  coagula- 
tion ;  whence  we  may  infer  that  it  contains  little  or  no  Fibrin.  It 
contains  Albumen  in  a  state  of  complete  solution,  as  we  may  ascer- 


PROGRESSIVE  ALTERATIONS  IN  THE  CHYLE.  301 

tain  by  the  influence  of  heat  or  acids  in  producing  coagulation.  And 
it  includes  a  quantity  of  fatty  matter,  which  is  not  dissolved,  but 
suspended  in  the  form  of  globules  of  variable  size.  The  quantity  of 
this  evidently  varies  with  the  character  of  the  food  ;  it  is  more  abund- 
ant, for  instance,  in  the  chyle  of  Man  and  the  Carnivora,  than  in 
that  of  the  Herbivora.  It  is  generally  supposed  that  the  milky  colour 
of  the  chyle  is  owing  to  the  oil-globules  ;  but  Mr.  Gulliver  has  pointed 
out  that  it  is  really  due  to  an  immense  multitude  of  far  more  minute 
particles,  w^hich  he  has  described  under  the  name  of  the  molecular 
base  of  the  chyle.  These  molecules  are  most  abundant  in  rich,  milky, 
opaque  chyle  ;  whilst  in  poorer  chyle,  which  is  semi-transparent,  the 
particles  float  separately,  and  often  exhibit  the  vivid  motions  common 
to  the  most  minute  molecules  of  various  substances.  Such  is  their 
minuteness,  that,  even  wdth  the  best  instruments,  it  is  impossible  to 
determine  either  their  form  or  their  dimensions  with  exactness;  they 
seem,  however,  to  be  generally  spherical ;  and  their  diameter  may 
be  estimated  at  between  l-36,000th  and  l-24,000th  of  an  inch. 
Their  chemical  nature  is  as  yet  uncertain  ;  they  are  remarkable  for 
their  unchangeableness,  when  submitted  to  the  action  of  numerous 
re-agents,  which  quickly  affect  the  proper  Chyle-corpuscles ;  whilst 
their  ready  solubility  in  Ether  would  seem  to  indicate  that  they  are  of 
an  oily  or  fatty  nature. 

517.  The  milky  aspect  which  the  serum  of  blood  sometimes  ex- 
hibits, is  due  to  an  admixture  of  this  molecular  base.  It  may  be  par- 
ticularly noticed,  when  blood  is  drawn  a  few  hours  after  a  full  meal, 
that  has  been  preceded  by  a  long  fast.  By  recent  experiments  it  has 
been  found,  that  the  serum  begins  to  show  this  turbidity,  about  half 
an  hour  after  the  meal  has  been  taken  ;  and  that  the  turbidity  increases 
for  some  hours  subsequently,  after  which  it  disappears.  The  period 
at  which  the  discoloration  is  greatest,  and  the  length  of  time  during 
which  it  continues,  vary  according  to  the  digestibility  of  the  food. 
When  the  serum  is  allowed  to  remain  at  rest,  the  opaque  matter  rises 
to  the  surface,  presenting  very  much  the  appearance  of  cream;  and 
when  separately  examined,  it  has  been  found  to  contain  a  proteine- 
compound,  mingled  with  oily  matter, — the  relative  amount  of  the 
two  appearing  to  depend  in  part  upon  the  characters  of  the  food  in- 
gested. Hence  it  would  not  seem  improbable,  that  the  molecular 
base  of  the  chyle  is  partly  derived  from  albuminous  matter  of  the 
food,  which  has  not  been  completely  dissolved  in  the  digestive  pro- 
cess, but  which  has  been  reduced  to  a  state  of  exceedingly  minute 
division  (§  473).  The  gradual  disappearance  of  the  turbidity  of  the 
serum  indicates  that  the  substance  which  occasioned  it  no  longer 
exists  as  such  in  the  circulating  current ;  being  either  drawn  off*  by 
the  nutritive  or  secretory  operations,  or  being  converted  by  the  as- 
similating process  into  the  ordinary  constituents  of  the  blood. 

518.  During  the  passage  of  the  Chyle  along  the  lacteals,  towards 
the  Mesenteric  glands,  it  undergoes  two  important  changes  ;  the  pre- 
sence of  Fibrin  begins  to  manifest  itself  by  the  spontaneous  coagula- 


302  PROGRESSIVE  ALTERATIONS  IN  THE  CHYLE. 

bility  of  the  fluid  ;  and  the  oil-globules  diminish  in  proportional 
amount.  The  fibrin  appears  to  be  formed  at  the  expense  of  the  albu- 
men; as  this  latter  ingredient  undergoes  a  slight  diminution.  It  is 
in  the  chyle  drawn  from  the  neighbourhood  of  the  mesenteric  glands, 
that  we  first  meet  with  the  peculiar  floating  cells  or  chyle-corpuscles, 
formerly  adverted  to  (§  212),  in  any  number.  The  average  diameter 
of  these  is  about  l-4600th  of  an  inch ;  but  they  vary  from  about 
l-700th  to  l-2600th,— that  is,  from  a  diameter  about  half  that  of  the 
human  blood-corpuscles,  to  a  size  about  a  third  larger.  This  varia- 
tion probably  depends  in  great  part  upon  the  period  of  their  growth. 
They  are  usually  minutely  granulated  on  the  surface,  seldom  exhibit- 
ing any  regular  nuclei,  even  when  treated  with  acetic  acid  ;  but  three  or 
four  central  particles  may  sometimes  be  distinguished  in  the  larger  ones. 
These  corpuscles  are  particularly  abundant  in  the  chyle  obtained  by 
puncturing  the  mesenteric  glands  themselves ;  and  there  can  be  little 
doubt,  that  they  are  identical  with  the  altered  epithelium-cells,  which 
line  the  lacteal  tubes  in  their  course  through  those  bodies  (§  496). 

519.  The  glandular  character  of  these  cells,  and  their  continued 
presence  in  the  circulating  fluid,  seem  to  indicate  that  they  have  an 
important  concern  in  the  process  of  Assimilation, — that  is,  in  the 
conversion  of  the  crude  elements  derived  from  the  food,  into  the 
organizable  matter  adapted  to  the  nutrition  of  the  body;  in  other 
words,  in  the  conversion  of  Albumen  into  Fibrin ;  which  change 
would  seem  to  take  place  to  a  considerable  extent  in  the  Mesenteric 
glands.  For  it  is  only  in  the  Chyle  which  is  drawn  from  the  lacteals 
intervening  between  the  mesenteric  glands  and  the  receptaculum 
chyli,  that  the  spontaneous  coagulability  of  the  fluid  is  so  complete  as 
to  produce  a  perfect  separation  into  clot  and  serum.  The  former  is  a 
consistent  mass,  which,  when  examined  with  the  microscope,  is  found 
to  include  many  of  the  chyle-corpuscles,  each  of  them  being  sur- 
rounded with  a  delicate  film  of  oil ;  the  latter  bears  a  close  resemblance 
to  the  serum  of  the  blood,  but  has  some  of  the  chyle-corpuscles  sus- 
pended in  it.  Considerable  differences  present  themselves,  however, 
both  in  the  perfection  of  the  coagulation,  and  in  its  duration.  Some- 
times the  chyle  sets  into  a  jelly-like  mass  ;  which,  without  any  sepa- 
ration into  coagulum  and  serum,  liquefies  again  at  the  end  of  half  an 
hour,  and  remains  in  this  state.  The  coagulation  is  usually  most 
complete  in  the  fluid  drawn  from  the  receptaculum  chyli  and  thoracic 
duct;  and  here  the  resemblance  between  the  floating  cells,  and  the 
white  or  colourless  corpuscles  of  the  blood,  becomes  very  striking. 

520.  The  Lymph,  or  fluid  of  the  Lymphatics,  differs  from  the 
Chyle,  as  already  remarked,  in  its  comparative  transparency  :  its 
want  of  the  opacity  or  opalescence,  which  is  characteristic  of  the 
latter,  being  due  to  the  absence,  not  merely  of  oil-globules,  but  also 
of  the  "molecular  base."  It  contains  floating  cells,  which  bear  a 
close  resemblance  to  those  of  the  Chyle  on  the  one  hand,  and  to  the 
colourless  corpuscles  of  the  Blood  on  the  other;  and  these,  as  in  the 
preceding  case,  are  most  numerous  in  the  fluid,  which  is  drawn  from 


ABSORPTION  FROM  EXTERNAL  AND  PULMONARY  SURFACE.     303 

the  lymphatics  that  have  passed  through  the  glands,  and  in  that  ob- 
tained from  the  glands  themselves.  Lymph  coagulates  like  chyle ; 
a  colourless  clot  being  formed,  which  encloses  the  greater  part  of 
the  corpuscles.  The  Lacteals  may  be  regarded  as  the  Lymphatics  of 
the  intestinal  walls  and  mesentery ;  performing  the  function  of  inter- 
stitial absorption,  as  well  as  effecting  the  introduction  of  alimentary 
substances  from  without.  During  the  intervals  of  digestion,  they 
contain  a  fluid,  which  is  in  all  respects  conformable  to  the  lymph  of 
the  lymphatic  trunks. 

521.  Thus  by  the  admixture  of  the  aliment  newly  introduced  from 
without,  with  the  matter  which  has  been  taken  up  in  the  various 
parts  of  the  system,  and  by  the  preparation  which  these  undergo  in 
their  course  towards  the  thoracic  duct,  a  fluid  is  prepared,  which 
bears  a  strong  resemblance  to  blood  in  every  particular,  save  the 
presence  of  red  corpuscles.  Even  these  may  sometimes  be  found  in 
the  contents  of  the  thoracic  duct,  in  sufficient  amount  to  communi- 
cate to  them  a  perceptible  red  tinge  ;  but  there  can  be  little  doubt 
that  they  have  found  their  way  thither  accidentally, — some  of  the 
lymphatic  or  lacteal  trunks,  which  have  been  divided  in  the  dissec- 
tion necessary  to  expose  the  duct,  having  taken  up  blood  by  their 
open  mouths,  and  rapidly  transmitted  it  into  the  general  receptacle. 
The  fluid  of  the  thoracic  duct  may  be  compared  to  the  blood  of 
Invertebrated  animals ;  from  which  the  red  corpuscles  are  almost  or 
altogether  absent ;  but  which  contains  white  or  colourless  corpuscles, 
and  which  possesses  but  a  slight  coagulating  power,  in  consequence 
of  its  small  proportion  of  fibrin.  And  we  hence  see,  why  these 
animals  should  require  no  special  absorbent  system ;  since  the  blood- 
vessels convey  a  fluid,  which  is  itself  so  analogous  to  the  chyle  and 
lymph  to  be  absorbed,  that  the  latter  may  be  at  once  introduced  into 
it,  without  injuring  its  qualities. 

5.  Absorption  from  the  External  and  Pulmonary  Surface. 

522.  Although  the  Mucous  Membrane  of  the  Alimentary  Canal  is 
the  special  channel  for  the  introduction  of  nutritive  or  other  sub- 
stances into  the  system,  it  is  by  no  means  the  only  one.  The  Skin 
covering  the  body,  and  the  Mucous  Membrane  prolonged  into  the 
Lungs,  are  also  capable  of  absorbing  liquids  and  vapours,  and  of 
introducing  them  into  the  Circulation;  although  they  serve  this  pur- 
pose less  in  Man  and  the  higher  animals,  than  in  some  of  the  lower. 
Their  utility  in  this  respect  is  best  shown,  when,  from  peculiar  cir- 
cumstances, the  function  of  the  digestive  cavity  cannot  be  properly 
performed;  and  when,  therefore,  the  system  has  been  more  than 
usually  drained  of  its  fluids,  and  stands  in  need  of  a  fresh  supply. — 
Thus  shipwrecked  sailors,  and  others,  who  are  suffering  from  thirst, 
owing  to  the  want  of  fresh  water,  find  it  greatly  alleviated,  or  alto- 
gether relieved,  by  dipping  their  clothes  into  the  sea,  and  putting 
them  on  whilst  still  wet,  or  by  frequently  immersing   their   own 


304  COMPOSITION  OF  THE  BLOOD. 

bodies.  In  a  case  of  dysphagia,  in  which  neither  solid  nor  fluid 
nutriment  could  be  introduced  into  the  stomach,  the  patient  was  kept 
alive  for  a  considerable  time,  and  his  sufferings  greatly  alleviated,  by 
the  administration  of  nutritive  clysters,  and  by  the  immersion  of  his 
body  in  a  bath  of  tepid  milk  and  water,  night  and  morning.  Under 
this  system,  the  weight  of  the  body,  which  had  previously  been 
rapidly  diminishing,  remained  stationary,  although  the  amount  of 
the  excretions  was  increased ;  and  the  use  of  the  bath  had  a  special 
influence  in  assuaging  the  thirst,  which  was  previously  distressing. 
It  appeared  that  the  w^ater  of  the  urinary  excretion,  amounting  to 
from  24  oz.  to  36  oz.  per  day,  must  have  been  entirely  supplied  from 
this  latter  source.  Again,  a  man  who  had  lost  nearly  3  lbs.  by  per- 
spiration, during  an  hour  and  a  quarter's  labour  in  a  very  hot  atmo- 
sphere, regained  8  oz.  by  immersion  in  a  warm  bath  at  95°  for  half 
an  hour. — In  these  cases  it  appears  probable,  from  the  experiments 
already  noticed  (§  502),  that  the  Lymphatics,  rather  than  the  blood- 
vessels, are  the  chief  agents  in  the  absorbing  process  ;  not,  however, 
from  any  powers  peculiar  to  them,  but  merely  on  account  of  the 
thinness  of  their  walls,  and  their  very  copious  distribution  in  the 
skin. 

523.  Absorption  may  also  take  place  from  an  atmosphere  saturated 
with  watery  vapour.  Of  this  we  have  a  very  curious  proof  in  the 
Frog;  whose  urinary  bladder  (which  serves  as  a  sort  of  reservoir  of 
water)  has  been  observed  to  be  refilled,  after  having  been  emptied, 
by  placing  the  animal  in  an  atmosphere  loaded  with  watery  vapour. 
Numerous  instances  are  on  record,  which  prove  that  such  absorption 
may  take  place  in  Man,  to  a  very  considerable  extent;  though  the 
proportion  introduced  through  the  Skin,  and  through  the  Lungs, 
cannot  be  exactly  ascertained.  The  ready  introduction  of  volatile 
matter  into  the  system,  through  the  latter  channel,  is  a  matter  of 
familiar  experience ;  thus  if  w^e  breathe  an  atmosphere  through  which 
the  vapour  of  turpentine  is  diffused,  it  soon  produces  the  character- 
istic odour  of  violets  in  the  urinary  secretion.  And  it  is  probably  in 
this  manner,  that  a  large  number  of  those  poisonous  miasmata  are 
introduced,  which  are  such  fertile  causes  of  disease. 

6.   Of  the  Composition  and  Properties  of  the  Blood. 

524.  Having  traced  the  steps  by  which  the  blood  is  elaborated,  and 
prepared  for  circulation  through  the  body,  and  having  (in  the  former 
part  of  the  volume)  inquired  into  the  characters  of  its  chief  constitu- 
ents, w-e  have  now^  to  consider  the  fluid  as  a  w^hole,  to  study  the  usual 
proportions  of  these  constituents,  and  the  properties  which  they  im- 
part to  it. 

525.  The  Blood,  whilst  circulating  in  the  living  vessels,  may  be 
seen  to  consist  of  a  transparent,  nearly  colourless  fluid,  termed  liquor 
sanguinis;  in  which  the  corpuscles^  to  which  the  blood  owes  its  red 
hue,  as  well  as  the  white  or  colourless  corpuscles,  are  freely  suspended 


COMPOSITION  OF  THE  BLOOD.  305 

and  carried  along  by  the  current. — On  the  other  hand,  when  the  blood 
has  been  drawn  from  the  body,  and  is  allowed  to  remain  at  rest,  a 
spontaneous  coagulation  takes  place,  separating  it  into  clot  and  serum. 
The  clot  is  composed  of  a  network  of  Fibrin,  in  the  meshes  of  w^hich 
the  Corpuscles,  both  red  and  colourless,  are  involved ;  and  the  serum 
is  the  same  w^ith  the  liquor  sanguinis  deprived  of  its  Fibrin.  When 
the  Serum  is  heated,  it  coagulates,  showing  the  presence  oi  Albumen, 
And  if  it  be  exposed  to  a  high  temperature,  sufficient  to  decompose 
the  animal  matter,  a  considerable  amount  of  earthy  and  alkaline  salts 
remains. — Thus  we  have  four  principal  components  in  the  Blood  ; — 
namely,  Fibrin,  Albumen,  Corpuscles,  and  Saline  matter.  In  the 
circulating  Blood  they  are  thus  combined  : — 

Fibrin  ^ 

Albumen  >      In  solution,  forming  Liquor  Sanguinis. 

Salts  ) 

Red  Corpuscles, — Suspended  in  Liquor  Sanguinis. 

But  in  coagulated  blood  they  are  thus  combined : — 

Fibrin 


-r,    ,  >^  ■,         i      Crassamentum  or  Clot. 

Ked  Corpuscles     J 

Albumen  ?       d        ...        i   ,.        r       •       o 

<^  ,  >      Remaming  in  solution,  lorming  Serum. 

A  certain  amount  of  Serum,  however,  is  involved  in  the  Crassa- 
mentum ;  and  can  only  be  separated  by  cutting  the  clot  into  thin 
slices,  and  carefully  washing  it. 

526.  The  components  of  the  Blood  may  be  separated,  and  their 
amount  estimated,  in  various  w^ays.  Thus,  if  fresh-drawn  blood  be 
continually  stirred  with  a  stick,  or  be  *' whipped,"  with  a  bunch  of 
twigs,  the  Fibrin  coagulates  in  the  form  of  strings,  which  adhere  to 
the  wood,  and  may  thus  be  withdrawn  ;  whilst  the  red  corpuscles  then 
remain  suspended  in  the  serum,  gradually  sinking  to  the  bottom  in 
virtue  of  their  greater  specific  gravity. — On  the  other  hand,  the  Red 
Corpuscles  may  be  separated,  in  those  animals  in  which  they  are  large 
enough,  by  passing  the  blood  through  a  filter ;  having  previously  min- 
gled with  it  some  substance,  w^hich  retards,  but  does  not  prevent  its 
coagulation*  (§  185).  The  liquor  sanguinis  is  thus  separated  from  the 
blood-discs ;  and  the  former  coagulates,  whilst  the  blood-discs  are 
retained  upon  the  filter.  This  experiment  convincingly  proves,  that 
the  act  of  coagulation  is  not  due  to  the  red  corpuscles,  as  was  at 
one  time  imagined.  The  ordinary  act  of  coagulation,  by  w^ithdraw- 
ing  the  Fibrin  and  Corpuscles,  makes  it  easy  to  estimate  the  propor- 
tion of  Albumen  and  of  Saline  matter  in  the  Blood,  when  due  allow- 
ance is  made  for  the  quantity  of  Serum  retained  in  the  Clot;  and  the 
relative  proportions  of  these  may  be  determined,  by  evaporating  the 

*  This  experiment  cannot  be  performed  with  Human  blood,  because  the  corpuscles 
are  small  enough  to  pass  through  the  pores  of  any  filter  that  allows  the  liquor  san- 
guinis to  permeate  it ;  but  it  answers  very  well  with  Frog's  blood. 

20 


306  COMPOSITION  OF  THE  BLOOD. 

fluid,  SO  as  to  obtain  the  whole  amount  of  solid  matter  it  contains,  and 
by  then  calcining  the  residuum,  so  as  to  ascertain  how  much  of  this  is 
a  mineral  ash, — the  remainder  being  chiefly  Albumen. — The  solid 
matter  of  the  blood  also  contains  various  Fatty  substances,  which 
may  be  removed  from  it  by  ether.  Some  of  these  appear  to  corre- 
spond with  the  constituents  of  ordinary  Fat  (§  261);  whilst  another 
contains  phosphorus,  and  seems  allied  to  the  peculiar  fatty  acids  of 
Neurine  (§  383);  and  another  has  some  of  the  properties  of  Choles- 
terine,  the  fatty  matter  of  the  Bile  (§  724). — Besides  these,  there  are 
certain  substances  known  under  the  name  of  Extractive;  one  group 
of  which  is  soluble  in  water  and  another  in  Alcohol.  Of  the  precise 
nature  of  these,  little  is  known.  They  have  been  aptly  termed  ''  ill- 
defined"  animal  principles  ;  and  it  is  probable  that  they  may  include 
various  substances  in  a  state  of  change  or  disintegration,  which  are 
being  eliminated  from  the  Blood  by  the  processes  of  Excretion. 

527.  The  general  result  of  numerous  recent  analyses  of  the  Blood 
may  be  thus  stated : — The  whole  amount  of  solid  matter  is  greater  in 
the  Male  than  in  the  Female.  The  higher  proportion  extends  to  all 
its  components  except  the  Albumen ;  and  this  is  almost  invariably 
present  in  an  amount,  which  is  absolutely  greater  in  1000  parts  of 
female  blood,  than  in  1000  parts  of  that  of  the  male,  and  which  is 
considerably  greater  in  proportion  to  the  other  solid  matters.  The 
proportion  of  Albumen  seems  more  constant  than  that  of  the  other 
constituents  of  Blood;  seldom  varying  beyond  5  or  6  parts  either 
more  or  less  than  70  in  1000. — The  quantity  of  Corpuscles  appears 
liable  to  considerably  greater  variation ;  the  superiority  on  the  side  of 
the  Male,  however,  being  very  strongly  marked  in  the  maximum  and 
minimum,  as  well  as  in  the  average.  We  may  regard  its  average 
in  the  Male  at  about  140  in  1000  parts  of  blood ;  but  it  may  fall  to 
110-5  parts,  without  the  health  being  seriously  aflected  ;  whilst,  on 
the  other  hand,  it  may  arise  to  186  without  any  manifestation  of  dis- 
ease. In  the  Female,  its  average  may  be  about  112  parts  in  1000; 
but  it  may  fall  to  as  little  as  71-4,  and  may  rise  to  167,  consistently 
with  ordinary  health.  The  range  of  variation  is  thus  much  greater  in 
the  Female  than  in  the  Male;  the  minimum  being  considerably  less 
in  the  former,  than  half  the  maximum  ;  whilst  in  the  latter,  it  is  much 
more.  This  is  probably  due  in  part  to  the  fact,  that  the  loss  by  the 
Catamenial  discharge  may  produce  a  great  temporary  depression  in  the 
proportion  of  the  corpuscles. — The  average  proportion  of  Fibrin  seems 
to  be  no  more  than  2*2  in  the  Male;  and  though  it  may  rise  to  as 
much  as  3*5  or  even  4,  without  disordering  the  system,  it  does  not 
seem  to  fall  below  2,  in  the  state  of  ordinary  health.  The  average  in 
the  Female  is  probably  about  2;  the  proportion  may  rise  to  3,  or  fall 
to  1*8;  but  the  variation  seems  less  considerable  in  the  Female  than 
in  the  Male. — Much  is  probably  yet  to  be  learned,  regarding  the  influ- 
ence of  different  kinds  of  food  recently  taken,  on  the  proportion  of 
these  constituents  of  the  blood  ;  and  it  does  not  seem  unlikely,  from 
what  has  been  already  stated  (§  517),  that  the  quantity  of  fatty  matter 


COMPOSITION  OF  THE  BLOOD.  307 

is  especially  liable  to  variation,  in  accordance  with  the  amount  con- 
tained in  the  food,  and  the  time  which  has  elapsed  since  the  last  meal. 

528.  The  Saline  constituents  of  the  blood,  obtained  by  drying  and 
incinerating  the  whole  mass,  usually  amount  to  between  6  and  7  parts 
in  1000.  More  than  half  of  their  total  quantity  is  composed  of  the 
Chlorides  of  Sodium  and  Potassium ;  and  the  remainder  is  made  up 
of  the  tribasic  Phosphate  of  Soda,  the  Phosphates  of  Lime  and  Mag- 
nesia, Sulphate  of  Soda,  and  a  little  Phosphate  and  Oxide  of  Iron. 
Of  these  the  chief  part  are  dissolved  in  the  Serum  ;  but  the  Earthy 
Phosphates,  which  are  insoluble  by  themselves,  are  probably  com- 
bined with  the  proteine-compounds  (§  175);  and  the  iron  is  contained, 
chiefly  or  entirely,  in  the  red  corpuscles.  It  is  difficult  to  speak  with 
certainty,  from  the  examination  of  the  ashes  of  the  blood,  as  to  the 
state  of  the  saline  constituents  of  the  circulating  fluid.  Thus,  the 
Serum  has  an  alkaline  reaction  ;  and  this  has  been  supposed  to  be  due 
to  the  presence  of  alkaline  Carbonates.  Moreover,  the  presence  of 
the  Lactates  of  potash  and  soda  has  been  usually  asserted.  On  the 
other  hand,  some  recent  analyses  would  indicate,  that  the  alkaline 
reaction  is  entirely  due  to  the  presence  of  the  tribasic  Phosphate  of 
soda  ;  and  that  no  alkaline  carbonates  or  lactates  exist  in  the  blood. 
This  discrepancy  seems  partly  due  to  the  mode  of  analysis  employed  ; 
for  it  has  been  lately  pointed  out  by  Dr.  G.  O.  Rees,  that  although 
the  ashes  of  the  entire  mass  of  blood  do  not  efl^ervesce  on  the  addition 
of  an  acid,  effervescence  takes  place,  when  acid  is  added  to  the  ashes 
of  the  Serum  ;  showing  the  existence  in  it,  either  of  alkaline  Carbon- 
ates, or  of  Lactates  which  have  been  reduced  to  the  state  of  Carbon- 
ates by  incineration.  It  appears  that  when  the  entire  mass  of  blood 
is  incinerated,  enough  phosphoric  acid  is  produced  from  the  phos- 
phorized  fats,  to  neutralize  the  alkaline  carbonates,  and  thus  to  pre- 
vent their  presence  from  being  recognized.  There  can  be  no  doubt, 
however,  that  the  tribasic  phosphate  of  soda  exists  as  such  in  the 
blood,  and  contributes  to  its  alkaline  reaction ;  and  it  appears  to  con- 
fer upon  the  serum  a  special  power  of  absorbing  carbonic  acid. 

529.  The  following  appear,  from  the  considerations  stated  in  the 
preceding  part  of  the  Volume,  to  be  the  chief  uses  of  the  principal 
constituents  of  the  Blood,  in  the  general  economy.  The  Fibrin  is 
the  material,  which  is  most  completely  prepared  for  organization,  and 
which  supplies  what  is  requisite  for  the  nutrition  of  the  larger  pro- 
portion of  the  solid  tissues  of  the  body.  It  is,  therefore,  being  con- 
tinually withdrawn  from  the  blood  by  the  nutritive  operations ;  and 
the  demand  appears  to  be  supplied,  in  part  by  the  influx  of  Fibrin 
that  has  been  prepared  in  the  Absorbent  system,  and  in  part  by  the 
continued  transformation  of  Albumen,  which  takes  place  during  the 
Circulation  of  the  Blood.  If  a  proper  amount  of  Fibrin  be  not  pre- 
sent in  the  Blood,  its  physical  properties  are  so  far  altered,  by  the 
diminution  of  its  viscidity,  that  it  will  not  circulate  through  the  capil- 
laries as  readily  as  before, — a  certain  degree  of  viscidity  having  been 
experimentally  found  to  be  favourable  to  the  movement  of  fluid 


308  COMPOSITION  OF  THE  BLOOD. 

through  glass  or  metallic  tubes  of  small  bore. — The  Albumen  of  the 
blood  is  the  raw  material,  at  the  expense  of  which  not  only  the  Fi- 
brin, but  many  other  substances  are  generated  during  the  nutritive 
process.  All  the  Albuminous  compounds  of  the  Secretions,  the 
Horny  matter  of  the  Epidermic  tissues,  the  Gelatin  of  the  simple 
fibrous  tissues,  the  solid  materials  of  the  Red  Corpuscles,  and  other 
substances,  may  be  regarded  as  almost  certainly  produced  by  the 
transformation  of  the  Albumen  of  the  Blood ;  and  a  continual  supply 
of  this  from  the  food  is  therefore  requisite,  to  preserve  the  due  pro- 
portion in  the  circulating  fluid. — The  Red  Corpuscles,  which  (it  will 
be  remembered)  are  almost  exclusively  confined  to  Vertebrated  ani- 
mals, appear  to  be  more  connected  with  the  function  of  Respiration, 
than  with  that  of  Nutrition  ;  and  the  stimulating  action  of  Arterial 
blood,  especially  upon  the  Muscular  and  Nervous  tissues,  appears 
chiefly  to  depend  upon  their  presence.  It  has  been  observed  in 
particular,  that  their  presence  is  more  effectual  in  stimulating  the 
heart's  action,  than  is  that  of  either  of  the  other  constituents  of  the 
blood.  In  addition  to  what  has  been  already  stated  (§  219),  in  re- 
ference to  their  continual  disintegration  and  renewal,  it  may  be  men- 
tioned, that  when  the  blood  of  one  animal  was  injected  by  Majendie 
into  the  veins  of  another  having  discs  of  very  different  size  and  form, 
the  original  Red  corpuscles  soon  disappeared,  and  were  replaced  by 
those  characteristic  of  the  species,  in  whose  veins  the  fluid  was  cir- 
culating. 

530.  The  use  of  the  Saline  matter  is  evidently  in  part  to  prevent 
decomposition  in  the  circulating  Blood  ;  but  also  to  supply  the  mineral 
materials,  requisite  for  the  generation  of  the  tissues,  and  entering  into 
the  composition  of  the  secretions.  It  is  by  the  saline  and  albuminous 
matters  in  conjunction,  that  the  specific  gravity  of  the  Liquor  Sangui- 
nis is  kept  up  to  the  point,  at  which  it  is  equivalent  to  that  of  the 
contents  of  the  Red  Corpuscles ;  and  it  is  only  in  this  condition,  that 
the  formation  of  the  latter  can  duly  take  place. — The  Fatty  matters 
of  the  Blood  are  evidently  derived  from  the  food,  either  directly,  or 
by  a  transformation  of  its  farinaceous  ingredients  (§  430) ;  and  they 
are  chiefly  appropriated  to  the  maintenance  of  the  combustive  process. 
That  which  may  be  superfluous  is  either  deposited  in  the  cells  of  Adi- 
pose Tissue,  or  it  is  eliminated  by  the  Liver,  the  Sebaceous  follicles 
of  the  Skin,  and,  in  the  female  when  nursing,  by  the  Mammary  glands. 
The  blood  appears  to  contain,  ready  formed,  the  peculiar  azotized  and 
phosphorized  fat  of  Nervous  matter;  but  how  this  is  generated, — 
whether  by  the  combination  of  azotized  and  phosphorized  ingredients 
with  ordinary  fat,  or  by  the  metamorphosis  of  albuminous  matter, — 
cannot  be  said  to  be  yet  determined. 

531.  The  proportion  of  these  components  of  the  Blood  is  liable  to 
undergo  changes  in  disease,  which  extend  far  beyond  the  widest  limits 
which  have  been  mentioned  as  consistent  with  health.  Thus,  the 
quantity  of  Fibrin  exhibits  a  remarkable  increase  in  Inflammation ; 
the  amount  then  found  in  the  blood  being  from  5  or  6  parts  in  1000 


COMPOSITION  OF  BLOOD  IN  DISEASE.  309 

to  9,  10,  or  even  lOJ,  according  to  the  extent  and  intensity  of  the 
disease.  On  the  other  hand,  it  presents  a  remarkable  diminution  in 
Typhoid  fevers ;  the  quantity  being  sometimes  as  little  as  0-9.  If 
any  decided  Inflammation  should  develop  itself,  however,  in  the 
course  of  the  Fever,  the  proportion  of  Fibrin  rises  accordingly.  A 
deficiency  of  Fibrin  in  the  blood  predisposes  to  Hemorrhages,  Con- 
gestions, &c.,  either  into  the  substance  of  the  tissues,  or  on  the  surface 
of  membranes  ;  and  these  conditions  are  well  known  to  be  of  frequent 
occurrence  as  complications  of  febrile  disorders.  An  excess  of  Fibrin 
is  not  much  affected  by  copious  bleeding,  even  if  this  be  frequently 
repeated ;  but  there  is  reason  to  think,  that  the  administration  of 
Mercury  has  a  tendency  to  restrain  its  production. 

532.  It  is  difficult  to  say  what  amount  of  Red  Corpuscles  should  be 
regarded  as  excessive ;  since,  as  we  have  seen,  they  may  augment  to 
a  great  degree,  without  disturbing  the  health.  When  they  are  present 
in  an  amount  much  above  the  average,  they  seem  concerned  in  pro- 
ducing the  condition  termed  Plethora  ;  which  marks  a  ''  high  condi- 
tion" of  the  system,  and  which  borders  upon  various  diseases,  espe- 
cially those  of  Congestion,  and  Hemorrhages.  To  these  a  peculiar 
liability  then  exists  ;  because,  although  the  proportion  of  Fibrin  in 
the  blood  is  not  absolutely  low,  it  is  low  in  reference  to  that  of  the 
Red  Corpuscles.  Plethoric  persons  do  not  seem  more  liable  to  In- 
flammation, than  are  those  of  weakly  constitution.  The  quantity  of  the 
Red  Corpuscles  is  rapidly  diminished  by  frequent  bleeding  ;  and  hence 
it  is  lowered  by  repeated  Hemorrhages.  On  the  other  hand,  it  is 
speedily  restored  to  its  usual  standard  under  the  influence  of  nutritious 
diet,  if  the  digestive  powers  have  not  been  too  much  weakened  to 
make  use  of  this. — The  proportion  of  Red  Corpuscles  undergoes  a 
marked  diminution  in  various  forms  of  Ansemia ;  and  particularly  in 
Chlorosis.  In  severe  cases  of  this  latter  disease,  it  has  been  found  as 
low  as  27  in  1000  ;  and  it  not  unfrequently  sinks  to  40  or  50.  The 
marked  influence  of  the  administration  of  Iron,  in  favouring  the  repro- 
duction of  Red  Corpuscles,  has  been  already  noticed  (§  219). 

533.  The  proportion  of  Albumen  in  the  Blood  seems  less  liable  to 
change,  except  in  the  condition  termed  Albuminuria,  in  which  a  large 
quantity  of  Albumen  appears  in  the  Urine.  When  this  condition  is 
permanently  established,  it  is  indicative  of  the  existence  of  serious 
organic  disease  of  the  kidney  ;  but  it  may  occur  for  a  short  time  under 
the  influence  of  simple  congestion  of  that  organ,  w^hich  causes  an 
escape  of  the  albuminous  part  of  the  blood,  together  with  the  water 
which  is  filtered-off  (as  it  were)  in  this  gland  (§  728).  Now  when 
Albuminuria  is  fully  established,  there  is  a  marked  diminution  in  the 
quantity  of  Albumen  in  the  serum  of  the  blood ;  and  this  diminution 
is  constantly  proportional  to  the  amount  of  Albumen  present  in  the 
Urine.  The  proportion  of  Saline  matter  appears  to  undergo  less  altera- 
tion in  disease  than  that  of  the  other  constituents  of  the  Blood ;  and 
has  not  been  found  to  have  a  regular  correspondence,  either  in  the 
way  of  excess  or  diminution,  with  any  particular  morbid  state. 


310  COAGULATION  OF  BLOOD. 

534.  The  condition  of  the  Blood  may  be  affected,  not  merely  by 
alteration  in  the  proportions  of  its  normal  ingredients,  but  by  the  pre- 
sence of  other  substances ; — either  such  as  are  generated  in  it,  and 
are  constantly  being  eliminated  from  it  in  health,  but  have  accumu- 
lated to  an  abnormal  degree  ; — or  such  as  have  found  their  way  into 
it  from  without.  Thus,  Carbonic  Acid,  Urea  and  Lithic  Acid,  Cho- 
lesterine  and  other  elements  of  Bile,  and  other  matters  which  it  is  the 
office  of  the  Excreting  organs  to  remove,  may  accumulate  in  the  blood, 
and  may  become  fertile  sources  of  disease,  by  their  injurious  influence. 
The  introduction  of  various  Mineral  substances,  by  absorption  from 
without,  changes  the  composition  of  the  normal  elements  of  the  Blood, 
and  thus  affects  their  vital  properties;  thus  strong  saline  solutions 
diminish  or  destroy  the  coagulating  power  of  the  Fibrin.  But  the 
most  remarkable  cases  of  depravation  of  the  Blood,  by  the  introduc- 
tion of  matters  from  without,  are  those  which  result  from  the  action  of 

ferments^ — exciting  such  Chemical  changes  in  the  constitution  of  the 
fluid,  that  its  whole  character  is  speedily  changed,  and  its  vital  pro- 
perties are  altogether  destroyed.  Of  such  an  occurrence  we  have  a 
marked  example  in  the  various  forms  of  malignant  fevers  ;  in  which 
the  introduction  of  a  very  minute  quantity  of  noxious  matter  into  the 
blood,  either  through  the  lungs  or  through  the  skin,  produces  a  speedy 
alteration  in  the  characters  of  the  whole  mass  of  the  blood,  the  func- 
tion of  every  organ  in  the  body  is  disordered,  and  decomposition  of 
the  solids  and  fluids  takes  place  to  a  considerable  extent,  even  before 
circulation  ceases,  and  whilst  consciousness  yet  remains.  The  train 
of  symptoms  produced  by  the  bite  of  venomous  Serpents,  and  of  rabid 
animals,  appears  referable  to  the  same  cause, — the  alteration  in  the 
condition  of  the  whole  current  of  blood,  by  the  introduction  of  a  minute 
quantity  of  a  substance  that  acts  as  a  ferment. 

535.  The  Coagulation  of  the  Blood,  as  already  explained,  depends 
upon  the  passage  of  its  Fibrin  from  the  fluid  state  to  the  solid  (§  184} ; 
consequently,  if  the  fibrin  be  separated  from  the  other  elements,  no 
coagulation  takes  place.  On  the  other  hand,  if  the  amount  of  Fibrin 
be  larger  than  ordinary,  the  coagulum  possesses  an  unusual  degree 
of  firmness.  The  length  of  time  which  elapses  before  coagulation, 
and  the  degree  in  which  the  Clot  solidifies,  vary  considerably;  in 
general  they  are  in  the  inverse  proportion  to  each  other.  Thus,  if  a 
large  quantity  of  blood  be  withdrawn  from  the  vessels  of  an  animal 
at  the  same  time,  or  within  short  intervals,  the  portions  that  last  flow 
coagulate  much  more  rapidly,  but  much  less  firmly,  than  those  first 
obtained,  in  consequence  of  the  diminished  proportion  of  fibrin.  On 
the  other  hand,  when  the  fibrin  is  in  excess,  its  coagulation  is  un- 
usually delayed.  From  this  delay  an  important  change  results,  in 
the  mode  in  which  the  coagulation  takes  place;  for  the  red  corpus- 
cles, instead  of  being  uniformly  diffused  through  the  coagulum,  have 
time  to  sink  to  the  bottom,  in  virtue  of  their  greater  specific  gravity; 
and  the  upper  part  of  the  clot  is  consequently  made  up  of  Fibrin, 
almost  exclusively,  whilst  the  lower  is  chiefly  formed  by  the  aggre- 


BUFFY  COAT. 


311 


gation  of  the  red  corpuscles.  Hence  the  upper  layer  is  almost  desti- 
tute of  colour,  (whence  it  has  received  the  name  of  huffy  coatj)  and 
is  remarkably  tenacious  in  its  character;  whilst  the  lower  is  very 
deep  in  hue,  and  very  friable  in  consistence.  When  the  fibrillated 
network  forming  the  buffy  coat  undergoes  the  slow  contraction,  which 
is  characteristic  of  highly-elaborated  fibrin  subsequently  to  its  coagu- 
lation, it  draws  in  the  edges  of  the  upper  surface  of  the  clot,  giving 
it  a  cupped  appearance. 

536.  The  BufTy  Coat  may  present  itself  under  a  great  variety  of 
conditions ;  and  it  can  no  longer,  therefore,  be  regarded  as  it  formerly 
was,  a  sign  of  the  Inflammatory  state.  It  is  most  fully  developed 
when  acute  Inflammation  exists  ;  because  in  that  condition  all  the  cir- 
cumstances which  favour  it  are  present.  That  it  may  be  produced 
by  any  cause,  which  occasions  delay  in  the  coagulation  of  the  blood, 
is  evident  from  the  fact,  that  healthy  blood  may  be  made  to  exhibit 
it,  by  adding  a  solution  of  a  neutral  salt,  which  retards,  but  does  not 
prevent  its  coagulation.  But  the  blood  may  coagulate  with  its  ordi- 
nary rapidity,  or  even  more  speedily  than  usual ;  and  may  yet  exhibit 
the  Bufiy  Coat.  And,  moreover,  the  separation  of  the  Fibrin  and 
the  Red  Corpuscles  may  take  place  in  films  of  blood  so  thin,  as  not 
to  admit  of  a  stratum  of  one  being  laid  over  the  other;  the  two 
elements  separating  from  each  other  laterally,  and  the  films  acquiring 
a  speckled  or  mottled  appearance,  equally  characteristic  of  the  In- 
flammatory condition  with  the  BuflTy  coat  itself.  Hence  the  separa- 
tion must  be  due  in  such  cases  to  other  causes  than  gravity,  and 
recent  observations  have  ac- 
counted for  it,  by  showing  that 
the  Red  Corpuscles  have  an  un- 
usual attraction  for  one  another 
in  the  Inflammatory  state,  causing 
their  coalescence  in  piles  and 
masses;  whilst  the  particles  of 
Fibrin  have  also  a  peculiarly 
strong  attraction  for  each  other. 
Thus  there  is  a  powerful  tend- 
ency, that  draws  together  the 
components  of  each  kind,  and 
consequently  tends  to  separate 
them  from  the  others ;  and  when 
this  separation  takes  place,  the 
difference  in  the  specific  gravity 
of  the  two  elements  decides 
their  respective  situations. — The 
peculiar  tendency  of  the  Red 
corpuscles  to  unite,  in  the  In- 
flammatory state,  serves  to  dis- 
tinguish this  condition,  even  in  a  single  drop  of  blood ;  and  it  is 
then  that  the  White  corpuscles  may  be  most  easily  distinguished,  as 


Fig.  S2. 


The  microscopic  appearance  of  a  drop  of  blood 
in  the  inflammatory  condition.  The  red  corpus- 
cles lose  their  circular  form,  and  adhere  together; 
the  white  corpuscles  remain  apart,  and  are  more 
abundant  than  usual. 


312  CIRCULATION  OP  BLOOD. 

they  are  seen  apart  from  the  rest  of  the  mass,  having  no  tendency  to 
unite  with  it.  In  fact,  the  white  corpuscles  are  not  found  in  com- 
pany with  the  red,  in  the  ordinary  coagulum,  but  rather  with  the 
fibrinous  portion ;  and  when  they  are  peculiarly  abundant,  as  they 
usually  are  in  Inflammatory  blood,  they  may  form  a  considerable  pro- 
portion of  the  buflfy  coat. 

537.  The  BufTy  Coat  may  present  itself,  without  the  least  increase 
in  the  normal  quantity  of  Fibrin,  and  without  any  approach  to  the 
Inflammatory  state ;  simply  because  the  Fibrin  is  present  in  exces- 
sive amount,  in  relation  to  the  amount  of  Red  corpuscles,  the  latter 
being  much  below  their  usual  proportion.  Thus  in  severe  Chlorosis, 
the  huffy  coat  is  almost  as  strongly  marked  as  in  the  severest  Inflam- 
mation ;  but  the  two  conditions  are  at  once  distinguished  by  the  rela- 
tive proportions  of  solid  matter  in  the  blood,  as  indicated  by  the  size 
of  the  Coagulum.  For  in  Chlorosis  the  coagulum  is  very  small,  in 
consequence  of  the  reduced  proportion  of  Corpuscles,  and  is  almost 
invariably  found  floating  in  the  serum ;  whilst  in  the  ordinary  Inflam- 
matory condition,  it  is  of  full  size,  frequently  adhering  to  the  side  of 
the  vessel. 


CHAPTER  VI. 

OF  THE  CIRCULATION  OF  THE  BLOOD. 

1.  JVature  and  Objects  of  the  Circulation  of  JSTutrient  Fluid. 

538.  The  nutritive  fluid, — the  elements  of  which  are  thus  chiefly 
taken  up  by  the  Absorbent  system,  and  are  there  prepared,  as  by 
glandular  apparatus  diffused  through  the  whole  body,  to  be  mingled 
with  the  general  mass  of  the  previously-formed  Blood, — is  carried  into 
the  various  parts  of  the  system,  by  the  act  of  Circulation.  This  move- 
ment answers  various  purposes.  It  furnishes  all  the  tissues,  which  are 
to  derive  nutriment  from  the  Blood,  with  a  constantly  renewed  supply 
of  the  materials  which  they  severally  require  ;  and  in  this  manner  it 
is  subservient  to  the  growth,  not  only  of  those  tissues  which  form 
part  of  the  solid  structure  of  the  body,  but  also  of  those  various  cells, 
covering  its  free  surfaces,  which  are  being  continually  cast  off*  and 
renewed,  and  which,  in  the  course  of  their  development,  separate  from 
the  blood  the  products  that  are  to  perform  ulterior  purposes  in  the 
economy,  or  are  to  be  cast  oflf  as  altogether  effete.  Thus  the  Circu- 
lation is  subservient  to  the  functions  of  Nutrition  and  Secretion.  In 
the  exercise  of  these  functions,  different  materials  are  drawn  from  the 
blood  by  the  several  tissues  it  supplies.  Thus  the  nutrition  of  the 
muscle  requires  fibrin  ;  that  of  the  nerve  requires  fatty-matter;  that  of 


CIRCULATION  OF  BLOOD.  313 

the  bone  draws  off  gelatin  and  earthy  salts ;  that  of  the  hepatic  cells 
removes  the  fatty  matter  and  other  elements  of  bile  ;  that  of  the  milk- 
cells  (during  lactation)  separates  albuminous,  fatty,  and  saccharine 
substances  ; — and  so  on.  Thus  various  portions  of  the  blood,  when 
returning  from  the  several  organs  through  which  they  have  been  trans- 
mitted, have  undergone  very  different  changes  by  the  nutritive  and 
secreting  processes,  according  to  the  function  of  the  organs  which  they 
have  supplied  ;  and  if  the  same  portion  of  the  circulating  fluid  were 
constantly  being  transmitted  to  each  organ,  and  returned  from  it,  its 
composition  would  speedily  undergo  a  change  that  would  render  it  no 
longer  fit  for  its  purposes.  By  the  union  of  the  different  local  circu- 
lations, however,  into  one  general  circulation,  this  change  is  pre- 
vented, and  the  whole  mass  of  the  blood  is  maintained  in  its  normal 
or  regular  condition ;  for  as  its  composition  is  such,  as  to  supply  all 
parts  of  the  body,  in  a  state  of  health,  with  the  proportions  of  nutri- 
tive material  which  they  respectively  need,  and  as  the  returning  cur- 
rents are  all  mingled  together  in  the  vessels,  before  being  again  dis- 
tributed to  the  system,  each  part  supplies  what  the  other  has  been 
deprived  of,  and  thus  the  normal  proportion  of  ingredients  in  the 
whole  mass  of  the  blood  is  constantly  kept  up,  whilst  in  each  of  its 
separate  streams  it  is  undergoing  an  alteration  of  a  different  kind. 

539.  But  these  processes  alone  might  be  carried  on  by  the  aid  of 
a  much  less  rapid  Circulation,  than  that  which  exists  in  Man  and  the 
higher  animals.  We  do,  in  fact,  occasionally  meet  with  examples,  in 
which  they  continue  for  some  time,  under  an  almost  total  stagnation 
of  the  current.  There  are  others,  however,  which  require  a  much 
more  rapid  and  uninterrupted  movement  of  the  circulating  fluid.  We 
have  already  seen  that,  for  the  action  of  the  Nervous  and  Muscular 
tissues,  oxygen  is  necessary ;  and  the  amount  of  that  gas  contained  in 
the  blood  circulating  through  these  tissues  would  be  very  speedily 
exhausted,  if  it  were  not  continually  renewed  ;  whilst  the  carbonic 
acid,  which  is  formed  at  the  expense  of  that  oxygen,  would  speedily 
accumulate  to  an  injurious  degree,  if  it  were  not  carried  off  as  fast  as 
it  is  produced.  Hence  we  find  that  in  all  Animals,  the  maintenance 
of  the  Respiration,  by  carrying  Oxygen  from  the  respiratory  surface 
into  the  different  parts  of  the  system,  and  by  conveying  back  Carbonic 
acid  to  be  thrown  ofl'  at  the  Respiratory  surface,  is  one  of  the  great 
purposes  of  the  Circulation  of  the  blood  ;  and  its  extreme  importance 
is  shown  by  the  very  speedy  check,  which  the  interruption  of  this 
function  produces  in  the  movement  of  the  blood,  in  warm-blooded 
animals.  Thus  in  a  Bird  or  Mammal,  completely  cut  off  from 
Oxygen,  the  circulation  in  the  lungs  will  come  to  a  stop,  which  stop- 
page will  necessarily  extend  itself  over  the  whole  body,  in  little  more 
than  three  minutes.'  We  find,  then,  that  the  rate  of  the  Circulation 
in  different  animals,  bears  a  relation  to  the  energy  of  their  Respiration  ; 
and  this  energy  is  closely  connected  with  the  general  activity  of  their 
functions,  but  particularly  with  that  of  the  Nervous  and  Muscular 
systems,  which  are  most  dependent  for  the  exercise  of  their  powers, 


314  ASCENT  OF  SAP  IN  PLANTS. 

upon  a  continually  fresh  supply  of  oxygen,  and  upon  the  unceasing 
removal  of  the  carbonic  acid  which  is  generated  in  their  substance. 

2.  Different  forms  of  the  Circulating  Apparatus. 

540.  It  is  desirable  that  the  Circulating  apparatus  should  be  first 
studied  in  its  very  simplest  form, — that  which  it  possesses  in  Plants 
and  in  the  lowest  tribes  of  Animals ;  as  in  this  way  alone  can  the 
forces,  which  are  concerned  in  the  movement  of  the  fluid,  be  rightly 
appreciated.  There  are,  in  all  the  higher  Plants,  two  distinct  cur- 
rents, that  of  the  ascending^  and  that  of  the  descending  sap.  The 
former  of  these  fluids  should  be  compared  rather  with  the  chyle  than 
with  the  blood  of  Animals  ;  for  it  is  a  crude  fluid,  not  yet  prepared  to 
take  part  in  the  nutrition  and  extension  of  the  structure.  But  there 
are  some  circumstances  attending  its  movement,  which  throw  light 
upon  other  more  complicated  phenomena.  The  ascending  sap  con- 
sists principally  of  water ;  which  is  imbibed,  together  with  various 
substances  which  it  holds  in  solution,  by  the  delicate  tissue  at  the  soft 
extremities  of  the  root-fibres,  or  spongioles.  The  power  of  forcing 
upwards  a  column  of  sap,  which  exists  in  these  bodies,  and  which 
seems  due  to  Endosmose  (§  491),  is  shown  by  very  simple  experi- 
ments. If  the  stem  of  a  Vine,  or  of  any  tree  in  which  the  sap  rises 
rapidly,  be  cut  across  when  in  full  leaf,  the  sap  continues  to  flow  from 
the  lower  extremity  ;  and  this  with  such  force,  as  to  distend  with  vio- 
lence, or  even  to  burst,  a  bladder  tied  firmly  over  the  cut  surface.  If 
instead  of  a  bladder,  a  bent  tube  be  attached  to  this,  and  mercury  be 
poured  into  it  so  as  to  indicate  the  pressure  exerted,  it  is  found  that 
the  rise  of  the  sap  takes  place  with  a  force  equal  to  the  pressure  of 
from  one  to  three  atmospheres  (from  15  to  45  lbs.  upon  the  square 
inch) — or  even  more.  Thus  the  ascent  of  the  sap  is  partly  due  to  a 
powerful  vis  a  tergo,  or  impelling  influence,  derived  from  the  point 
where  the  absorption  takes  place. 

541.  But,  on  the  other  hand,  if  the  upper  extremity  be  placed  with 
the  cut  surface  of  the  stem  in  water,  a  continued  absorption  of  that 
fluid  will  take  place,  as  is  evidenced  by  the  withdrawal  of  the  water 
from  the  vessel ;  the  fluid  which  is  thus  taken  up,  however,  is  not 
retained  w^ithin  the  stem  and  branches,  but  is  carried  into  the  leaves, 
and  is  thence  dissipated  by  exhalation.  It  is  obvious,  then,  that  the 
vis  a  tergo  is  not  the  sole  cause  of  the  ascent  of  the  sap ;  but  that  a 
vis  afronte  also  exists,  by  which  the  fluid  is  drawn  towards  the  paVts 
in  which  it  is  to  be  employed.  This  is  further  made  apparent  by  a 
few  simple  experiments.  If  a  branch,  when  thus  actively  absorbing 
fluid,  be  carried  into  a  dark  room,  the  absorption  and  ascent  of  fluid 
immediately  cease  almost  completely ;  and  are  renewed  again,  so  soon 
as  the  leaves  are  again  exposed  to  light.  Now  w^e  know,  from  other 
experiments,  that  light  stimulates  the  exhaling  process  (§  87),  whilst 
darkness  checks  it;  and  the  cessation  of  the  demand  in  the  leaves 
thus  produces  a  cessation  in  the  absorption  at  the  lower  extremity  of 


ASCENT  AND  DESCENT  OF  SAP  IN  PLANTS.         315 

the  stem.  And  this  is  the  case  also,  in  the  natural  condition  of  the 
plant;  as  is  easily  shown  by  immersing  the  roots  in  water,  and  ob- 
serving the  respective  quantities  which  are  removed  by  absorption 
during  sunshine,  shade,  and  darkness.  On  the  other  hand,  the  move- 
ment of  the  sap  may  be  excited,  when  it  would  not  otherwise  take 
place,  by  the  production  of  a  demand  at  the  extremities  of  the 
branches;  thus  if  a  branch  of  a  vine  growing  in  the  open  air,  be 
introduced  into  a  hot-house,  and  be  subjected  to  artificial  heat  during 
winter,  its  buds  will  be  developed,  its  leaves  will  expand,  and  these 
will  draw  fluid  to  themselves  through  the  roots  and  stem,  which  are 
still  inactive  as  regards  the  remainder  of  the  tree.  And  the  natural 
commencement  of  the  movement  of  the  ascending  sap,  which  takes 
place  with  the  returning  warmth  of  spring,  has  been  experimentally 
shown  to  occur,  in  the  first  instance,  not  in  the  neighbourhood  of  the 
roots,  but  nearest  the  extremities  of  the  branches ;  the  exhalation  of 
fluid  from  the  expanding  buds  being  the  first  process,  and  a  demand 
for  fluid  being  thus  created,  which  is  supplied  by  the  flow  that  is  thus 
excited  in  the  lower  part  of  the  stem, — this,  again,  being  supplied 
from  the  roots,  which  are  thus  caused  to  recommence  their  absorbent 
function. 

542.  Thus  we  see  that,  in  the  ascending  sap,  the  movement  is  en- 
tirely regulated  by  the  demand  for  fluid,  occasioned  by  the  actions  of 
the  leaves ;  even  though  it  is  in  great  part  dependent  on  the  vis  a  tergo, 
which  has  its  seat  in  the  spongioles.  Not  even  this  force,  however, 
— powerful  as  it  has  been  shown  to  be, — can  produce  the  continu- 
ance of  the  upward  flow,  when  the  exhalation  from  the  leaves  is 
checked  by  darkness,  and  when  the  demand  occasioned  by  the  action 
of  these  organs  is  consequently  suspended. 

543.  The  movement  of  the  descending  sap  offers  numerous  points, 
which  deserve  to  be  carefully  considered.  This  fluid  is  strictly  com- 
parable to  the  blood  of  animals;  having  undergone  a  preparation  or 
elaboration  in  the  leaves,  which  adapts  it  to  the  nutrition  and  exten- 
sion of  the  structure,  and  to  the  formation  of  the  various  secretions 
of  the  plant.  A  great  part  of  the  fluid  of  the  ascending  sap  has  been 
lost  by  exhalation  ;  and  the  remainder,  thus  concentrated,  receives  a 
large  additional  supply  of  solid  matter  through  the  agency  of  the  green 
cells  of  the  leafy  parts,  which  take  in  carbon  from  the  atmosphere 
(§  83) ;  so  that  it  now  includes  a  considerable  amount  of  gummy 
matter,  in  the  state  prepared  for  being  converted  into  solid  tissue ;  as 
well  as  numerous  other  compounds.  Now  this  elaborated  sap  is  then 
conveyed  into  the  various  parts  of  the  system,  through  the  agency  of 
a  network  of  vessels,  which  takes  its  origin  in  the  leaves,  and  extends 
along  the  branches  to  the  stem  and  roots,  chiefly  in  the  bark  of  those 
parts.  These  vessels  are  strictly  analogous  to  the  capillaries  or  small- 
est blood-vessels  of  Animals ;  but  they  differ  from  them  in  this, — 
that  the  capillary  network  of  Animals  communicates  on  either  side 
with  larger  trunks,  being  formed,  in  fact,  by  the  interlacement  or 
anastomosis  of  their  minutest  branches, — whilst  the  network  of  nutri- 


316  CIRCULATION  OF  ELABORATED  SAP. 

live  vessels  in  Plants  is  everywhere  continuous  with  itself,  not  having 
any  communication  with  large  vessels,  so  that  the  fluid  prepared  in 
the  leaves  commences  a  circulation  there,  which  is  continued  on  the 
same  plan,  until  it  has  found  its  way  to  its  remote  destination  in  the 
roots. 

544.  The  natural  movement  of  the  elaborated  sap  through  these 
vessels  may  be  studied,  under  favourable  circumstances,  with  the 
assistance  of  the  microscope  ;  the  requisite  conditions  being,  that  the 
part  should  be  sufficiently  transparent  for  the  vessels  to  be  distinctly 
seen,  that  the  sap  shall  contain  globules  in  sufficient  number  to  allow 
its  movement  to  be  distinguished  by  their  means,  and  that  the  circu- 
lation should  be  observed  without  the  separation  of  the  organ  exam- 
ined from  the  rest  of  the  Plant,  which  would  produce  irregular  move- 
ments, by  the  escape  of  the  sap  from  the  wounded  part.  These 
conditions  may  be  attained  in  many  Plants; — most  conveniently, 
perhaps,  in  the  stipules  of  the  Ficus  elastica,  one  of  the  trees  which 
affi^rds  the  largest  supplies  of  Caoutchouc  ;  and  it  is  then  found  that 
the  movement  takes  place  in  the  following  manner.  Distinct  currents 
are  seen,  passing  along  the  straightest  and  most  continuous  vessels, 
and  crossing  by  the  lateral  connecting  branches  of  the  network. 
These  currents  follow  no  determinate  direction;  some  proceeding  up, 
and  others  down ;  some  to  the  left,  and  others  to  the  right :  not  un- 
frequently  a  complete  stoppage  is  seen  in  one  or  more  of  the  channels, 
without  any  obvious  obstruction  ;  and  the  movement  then  recom- 
mences, perhaps,  in  the  opposite  direction.  The  influence  of  a  force, 
developed  by  the  act  of  circulation,  which  determines  the  direction  of 
the  movement,  appears  from  this ;  that  if  a  tube  be  cut  off',  so  as  to 
give  its  contents  an  equally  free  exit  at  both  ends,  the  sap  only  flows 
out  at  one  extremity.  The  movement  is  retarded  by  lowering  the 
temperature  of  the  surrounding  air,  and  it  is  completely  checked  by 
extreme  cold  ;  it  is  capable  of  being  renewed  by  moderate  warmth  ; 
and  a  further  addition  of  heat  increases  its  rapidity.  By  a  strong 
electric  shock,  the  force  by  which  the  latex  is  propelled  seems  to  be 
altogether  destroyed  ;  for  the  movement  then  ceases  entirely. 

545.  Now  it  is  quite  certain  that  this  circulation  cannot  be  due  to 
any  m5  a  tergo ;  both  because  it  is  not  constant  in  its  direction  in 
particular  vessels ;  and  because  there  is  no  organ  in  which  any  pro- 
pelling force,  that  could  extend  itself  through  such  a  complex  system 
of  vessels,  may  be  developed.  Nor  can  it  be  in  any  way  due  to 
the  force  of  gravity ;  for  although  this  may  assist  the  descent  of  the 
fluid  through  the  stem,  it  is  totally  opposed  to  its  ascent  from  the  ends 
of  its  branches  towards  their  origin,  when,  as  often  happens,  the 
latter  are  at  the  higher  level.  Moreover,  it  may  be  noticed  that  this 
circulation  takes  place  most  readily,  in  parts  that  are  undergoing  a 
rapid  development;  and  that  its  energy  corresponds  with  the  vitality 
of  the  part.  Further,  it  may  be  observed  to  continue  for  some  time 
in  parts  that  have  been  completely  detached  from  the  rest;  and  on 
which  neither  vis  a  tergo,  nor  vis  a  fronte,  can  have  any  influence. 


CIRCULATION  OF  ELABORATED  SAP.  317 

It  is  evident,  then,  that  the  force, — whatever  be  its  nature, — by  which 
this  continued  movement  is  kept  up,  must  be  developed  by  the  pro- 
cesses to  which  that  movement  is  subservient ;  in  other  words,  that 
the  changes  involved  in  the  acts  of  nutrition  and  secretion  are  the 
real  source  of  the  motor  power.  The  manner  in  which  they  become 
so,  is  the  next  object  of  our  inquiry ;  and  on  this  subject,  some  new 
views  have  recently  been  put  forth  by  Prof.  Draper,  which  seem  to 
account  well  for  the  phenomena. 

546.  It  is  capable  of  being  shown,  by  experiments  on  inorganic 
bodies,  that,  if  two  liquids  communicate  with  each  other  through  a 
capillary  tube,  for  the  walls  of  which  they  both  have  an  affinity,  but 
this  affinity  is  stronger  in  the  one  liquid  than  in  the  other,  a  move- 
ment will  ensue  ;  the  liquid  which  has  the  greatest  affinity  being 
absorbed  most  energetically  into  the  tube,  and  driving  the  other 
before  it.  The  same  result  occurs  when  the  fluid  is  drawn,  not  into 
a  single  tube,  but  into  a  network  of  tubes,  permeating  a  solid  struc- 
ture ;  for  if  this  porous  structure  be  previously  saturated  with  the 
fluid,  for  which  it  has  the  less  degree  of  attraction,  this  will  be  driven 
out  and  replaced  by  that  for  which  it  has  the  greater  affinity,  when  it 
is  permitted  to  absorb  this.  Now  if,  in  its  passage  through  the  porous 
solid,  the  liquid  undergoes  such  a  change,  that  its  affinity  be  dimin- 
ished, it  is  obvious  that,  according  to  the  principle  just  explained,  it 
must  be  driven  out  by  a  fresh  supply  of  the  original  liquid,  and  that 
thus  a  continual  movement  in  the  same  direction  would  be  produced. 

547.  Now  this  is  precisely  that  which  seems  to  take  place  in  the 
organized  tissue,  permeated  by  nutritious  fluid.  The  particles  of  this 
fluid,  and  the  solid  matter  through  which  it  is  distributed,  have  a  cer- 
tain affinity  for  each  other  ;  which  is  exercised  in  the  nutritive  changes, 
to  which  the  fluid  becomes  subservient  during  the  course  of  its  circu- 
lation. Certain  matters  are  drawn  from  it,  in  one  part,  for  the  sup- 
port and  increase  of  the  woody  tissue ;  in  another  part,  the  secreting 
cells  demand  the  materials  which  are  requisite  for  their  growth, — as 
starch,  oil,  resin,  &c.;  and  thus  in  every  part  that  is  traversed  by  the 
vessels,  there  are  certain  affinities  between  the  solids  and  the  fluids, 
which  are  continually  being  newly  developed  by  acts  of  growth,  as 
fast  as  those  which  previously  existed  are  satisfied  or  neutralized  by 
the  changes  that  have  already  occurred.  Thus  in  the  circulation  of 
the  elaborated  sap,  there  is  a  constant  attraction  of  its  particles 
towards  the  walls  of  the  vessels,  and  a  continual  series  of  changes 
produced  in  the  fluid,  as  the  result  of  that  attraction.  .The  fluid, 
which  has  given  up  to  a  certain  tissue  some  of  its  materials,  no 
longer  has  the  same  attraction  for  that  tissue  ;  and  it  is  consequently 
driven  from  it  by  the  superior  attraction,  then  possessed  by  the  tissue 
for  another  portion  of  the  fluid,  which  is  ready  to  undergo  the  same 
changes,  to  be  in  its  turn  rejected  for  a  fresh  supply.  Thus  in  a 
growing  part,  there  is  a  constantly  renewed  attraction  for  the  nutritive 
fluid,  which  has  not  yet  traversed  it ;  whilst,  on  the  other  hand,  there 
is  a  diminished  attraction  for  the  fluid,  which  has  yielded  up  the  nu- 


318  CIRCULATION  IN  PLANTS  AND  LOWER  ANIMALS. 

tritive  materials  required  by  the  particular  tissues  of  the  part;  and  thus 
the  former  is  continually  driving  the  latter  before  it. 

548.  But  the  fluid  which  is  thus  repelled  from  one  part,  may  still 
be  attracted  towards  another ;  because  that  portion  of  its  contents, 
which  the  latter  requires,  may  not  yet  have  been  removed  from  it. 
And  in  this  manner,  it  w^ould  seem,  the  flow  of  sap  is  maintained, 
through  the  whole  capillary  network,  until  it  is  altogether  exhausted 
of  its  nutritive  matter.  The  source  of  the  movement  is  thus  entirely 
to  be  looked  for  in  the  changes,  which  take  place  in  the  act  of  growth  ; 
and  the  influence  of  heat,  cold,  and  other  agents,  upon  the  movement, 
is  exercised  through  their  power  of  accelerating  or  retarding  those 
changes. — The  fluid  which  thus  descends  through  the  stem  and  roots, 
seems  to  be  at  last  almost  entirely  exhausted  ;  a  portion  of  it  appears 
to  find  its  way  into  the  ascending  current,  and  to  be  mingled  with 
the  ascending  current;  but  all  the  rest  seems  to  have  been  entirely 
appropriated  by  the  different  tissues,  through  which  it  has  circulated. 
Thus  there  is  no  need  of  any  general  receptacle,  into  which  it  may  be 
collected,  and  from  which  it  may  take  a  fresh  departure  ;  such  as  is 
afforded  by  the  heart  of  Animals.  And  as  the  purpose  of  this  circu- 
lation is  only  to  supply  the  nutritive  materials,  and  not  to  convey 
oxygen, — this  element  being  but  little  required  in  the  vegetative  pro- 
cesses, and  being  supplied  by  other  means, — the  same  energy  and 
rapidity  are  not  required  in  it,  as  need  to  be  provided  for  in  the  higher 
Animals. 

549.  A  condition  of  the  Circulating  system  very  similar  to  this, 
exists  in  several  of  the  lower  Animals,  as  well  as  in  the  embryo-state 
of  the  higher.  In  the  very  lowest,  no  blood-vessels  are  required,  for 
the  same  reason  that  no  sap- vessels  exist  in  the  lowest  Plants ; — 
namely,  because  every  part  absorbs  and  assimilates  nutritious  fluid  for 
itself,  so  that  it  does  not  require  a  supply  from  vessels.  As,  in  the 
Sea-Weeds,  the  whole  substance  is  nourished  by  direct  absorption 
from  the  fluid  in  contact  with  the  external  surface,  every  part  of  which 
seems  endowed  with  the  same  absorbent  power,  so  in  the  Polypes  do 
we  find,  that  the  whole  substance  is  nourished  by  direct  absorption 
from  the  internal  surface,  w^hich  forms  the  lining  of  the  digestive 
cavity.  In  the  same  manner,  the  Aeration  of  the  animal  fluids, — or 
the  exposure  of  them  to  the  air  contained  in  water,  by  which  they  may 
part  with  carbonic  acid  and  imbibe  oxygen, — is  provided  for,  not  by 
any  special  respiratory  organs,  but  by  the  contact  of  water  with  every 
part  of  the  soft  external  and  internal  surfaces.  Further,  as  the  sub- 
stance of  their  body  is  nearly  of  the  same  kind  in  every  part,  they  do 
not  require  the  continual  interchange  of  the  fluid  distributed  to  its 
several  portions.  Thus  no  circulation  is  necessary,  in  these  simple 
animals,  either  for  the  nutrition  of  their  tissues,  or  for  the  aeration  of 
the  fluids.  The  same  is  the  case  with  others  of  the  lower  tribes  ;  as 
well  as  with  the  embryo  of  the  higher  Animals,  at  the  earliest  periods 
of  their  development.  Thus  the  lower  Entozoa,  or  parasitic  worms, 
have  a  digestive  cavity  channeled  out,  as  it  were,  in  their  soft  gela- 


CIRCULATION  IN  LOWER  ANIMALS,  AND  IN  EMBRYO. 


319 


tinous  tissues;  and  from  the  walls  of  this,  the  nourishment  is  drawn 
by  the  several  component  parts  of  those  tissues,  without  the  mediation 
of  vessels.  And  the  embryo  even  of  Man,  in  its  early  condition, 
consists  of  an  aggregation  of  cells,  each  of  which  absorbs  for  itself 
from  the  nutritious  fluid  with  which  it  is  surrounded,  and  goes  through 
all  its  functions  independently  of  the  rest. 

550.  Proceeding  a  little  higher,  we  find  the  first  appearance  of 
proper  vessels  in  the  higher  Entozoa,  and  in  the  Mcalephce  or  Jelly- 
fish. These  vessels  take  up  the  nutritive  fluid  from  the  walls  of  the 
digestive  cavity,  on  which  they  are  spread  out,  just  as  the  roots  of 
Plants  do  from  the  soil.  They  then  unite  into  trunks,  by  which  the 
fluid  is  conveyed  to  the  more  distant  parts  of  the  structure,  in  the 
same  manner  as  the  ascending  sap  is  conveyed  to  the  leaves  by  the 
vessels  of  the  stem  and  branches ;  and  these  trunks  again  subdivide, 
and  form  a  network  of  capillary  vessels,  which  are  dispersed  through 
the  several  parts  of  the  fabric ;  some  of  them  being  very  abundantly 
distributed  upon  a  portion  of  the  surface,  which  "is  particularly  destined 
to  perform  the  respiratory  function.  Through  these  capillary  vessels, 
the  fluid  seems  to  move  in  very  much  the  same  manner,  as  through 
the  system  of  anastomosing  vessels  in  Plants ; — that  is,  its  motion  is 
due,  rather  to  forces  which  are  developed  during  its  circulation,  than 
to  any  vis  a  tergo  derived  from  the  contractile  power  of  a  propelling 
organ.  But  there  is  this  diflference ;  that,  after  having  traversed  the 
minute  vessels,  and  yielded  up  to  the  tissues  a  part  of  the  solid  matter 
which  it  contains,  the  fluid  is  collected  again  by  other  trunks,  which 
convey  it  back  to  the  point  from 
which  it  started ;  there  it  is  min- 
gled with  the  fluid  that  has  been 
newly  absorbed,  and  with  that 
which  has  undergone  aeration  ; 
and  it  is  then  distributed,  as  be- 
fore, through  the  general  capil- 
lary network  of  the  body. 

551.  Now  this  is  very  much 
the  condition  of  the  human  em- 
bryo, at  the  time  when  vessels 
are  first  developed  in  its  sub- 
stance. These  vessels  are  form- 
ed by  the  coalescence  of  cells; 
and  from  the  contents  of  these 
cells,  which  have  been  imbibed 
from  the  yelk,  the  first  blood 
seems  to  be  derived.  The  first 
formation  of  blood-vessels  takes 
place,  not  in  that  part  of  the  em- 
bryonic structure  which  is  to  be 
developed  into  the  perfect  animal,  but  in  a  membranous  expansion 
from  it,  which  surrounds  the  yelk,  and  which  answers  the  purpose  of 


Vascular  Area  of  Fowl's  egg,  at  the  beginning  of 
the  third  day  of  incubation ;— a,  a,  yelk;  b,  b,  b,  b, 
venous  sinus  bounding  the  area:  c,  aorta;  d,  punc- 
tum  saliens,  or  incipient  heart;  e,  e,  area  pellucida; 
/,/,  arteries  of  the  vascular  area;  g-jg,  veins;  A,  eye. 


320  CIRCULATION  IN  LOWER  ANIMALS. 

a  temporary  stomach.  A  capillary  network  is  formed  in  a  limited 
portion  of  this  membrane,  termed  the  vascular  area  (Fig.  83)  ;  and 
this  not  by  the  branching  of  larger  trunks,  these  trunks  being  subse- 
quently formed  by  the  reunion  of  the  capillaries.  The  first  movement 
of  the  blood  is  towards  the  central  spot,  in  which  the  organs  of  the 
permanent  structure  are  being  evolved ;  and  it  takes  place  before  the 
incipient  heart  has  acquired  any  muscularity,  so  that  it  must  be  quite 
independent  of  any  contractile  force  exerted  by  that  organ.  Here 
too,  then,  we  perceive  that  the  circulation  is  essentially  capillary ;  and 
that  it  is  sustained  by  forces  very  different  from  those,  of  which  the 
action  is  most  evident  to  us  in  the  higher  animals. 

552.  As  we  ascend  the  animal  scale,  however,  we  find  that  pro- 
vision is  made  for  a  more  regular  and  vigorous  Circulation  of  the 
Blood,  than  that  which  exists  in  the  lowest  classes.  Thus  in  the 
class  of  Echinodermata  (including  the  Star-fish  and  Sea-Urchin),  a 
portion  of  the  principal  vessel  is  peculiarly  endowed  with  contractile 
power;  and  this  may  be  seen  in  constant  pulsation,  like  the  heart  of 
the  higher  animals, — alternately  contracting,  to  propel  the  fluid  it 
contains,  through  the  vessels  that  issue  from  it, — and  then  dilating, 
to  receive  a  fresh  supply  from  the  vessels  that  pour  their  contents 
into  it.  A  similar  provision  is  observable  in  the  lower  tribes  of 
Worms,  in  which  this  contractile  vessel  lies  along  the  back ;  pro- 
pelling the  blood  forwards,  by  a  sort  of  peristaltic  movement,  through 
trunks  which  pass  out  at  its  anterior  termination ;  and  receiving  it 
again,  after  it  has  circulated  through  the  system,  by  vessels  which 
enter  at  its  posterior  extremity.  In  the  higher  orders  of  Worms,  in 
the  Myriapoda  or  Centipede  tribe,  and  in  Insects,  we  find  this  dorsal 
vessel  divided  by  transverse  partitions  containing  valves,  into  separate 
cavities  which  answer  to  the  different  segments  of  the  body.  Each 
of  these  is,  to  a  certain  extent,  the  heart  of  its  own  segment,  receiving 
and  propelling  blood  by  trunks  which  open  into  it ;  but  they  all  par- 
ticipate in  the  more  general  circulation  just  described,  a  large  portion 
of  the  blood  being  poured  into  the  hindermost  segment,  transmitted 
forwards  from  cavity  to  cavity  through  the  valves  which  separate 
them,  and  at  last  propelled  through  trunks  that  issue  from  the  most 
anterior  segment.  In  some  instances  we  find  that  two  or  three  of 
these  trunks,  on  either  side,  pass  round  the  oesophagus,  and  reunite 
below  it,  so  as  to  enclose  it  in  a  sort  of  collar ;  and  they  form  a  main 
trunk  by  this  union,  which  runs  backwards  along  the  under  surface  of 
the  body,  and  which  distributes  the  blood  to  its  different  organs  by 
lateral  branches.  These  subdivide  into  a  capillary  network  ;  and  the 
returning  vessels,  w^hich  originate  in  this  network,  pour  the  blood 
which  has  circulated  through  it  into  the  posterior  cavity  of  the  dorsal 
vessel. — Still  it  is  very  evident,  from  the  observation  of  the  circulation 
in  those  transparent  species,  in  which  the  whole  process  can  be  dis- 
tinctly watched  under  the  Microscope,  that  the  contractile  power  of 
the  dorsal  vessel  is  far  from  sufficient  of  itself  to  sustain  the  Circula- 
tion ;  and  that  the  movement  of  the  blood  through  the  capillary  net- 


CIRCULATION  IN  ARTICULATED  CLASSES.  321 

work  is  in  part  due  to  forces  developed  during  its  progress, — being 
often  retarded  or  accelerated  in  particular  spots,  without  any  visible 
change  in  the  propelling  force  of  the  central  organ. 

553.  In  most  of  these  animals,  there  are  distinct  organs  of  Respi- 
ration, confined  to  some  one  part  of  the  body ;  and  we  often  find  that 
the  vessels  which  convey  blood  to  them,  are  furnished  with  distinct 
contractile  portions,  like  so  many  supplementary  hearts,  for  the  pur- 
pose of  propelling  the  blood  through  thera  more  energetically.  In 
proportion  as  we  ascend  the  series  of  Articulated  animals,  do  we  find, 
for  the  most  part,  a  more  vigorous  and  regular  circulation,  both  for 
the  nutrition  of  the  system,  and  for  the  transmission  of  the  blood 
through  the  respiratory  organs ;  but  there  is  an  exception  in  the  case 
of  Insects,  which  deserves  special  notice.  In  this  class,  the  circula- 
tion is  much  less  vigorous  than  it  is  in  other  Articulated  animals  of 
similar  complexity  of  structure ;  though  it  might  have  been  antici- 
pated, that  the  extraordinary  activity  of  their  movements  would  ne- 
cessitate a  corresponding  rapidity  in  the  circulating  current,  espe- 
cially for  the  purpose  of  conveying  an  extraordinary  supply  of  oxygen 
to  the  nervous  and  muscular  systems.  But  this  is  provided  for  in 
another  way ;  the  air  being  conveyed  to  these  tissues,  not  through 
the  blood,  but  by  direct  transmission  through  the  minute  ramifications 
of  the  air-tubes  or  tracheae,  which  penetrate  the  very  smallest  organs  of 
the  body. 

554.  The  condition  of  the  Circulating  apparatus  in  the  Embryo  of 
higher  animals,  at  a  period  a  little  advanced  beyond  that  just  alluded 
to,  presents  a  striking  analogy  with  that  last  described  ;  for  the  heart, 
at  the  time  of  its  first  formation,  seems  like  a  mere  dilatation  of  the 
principal  vascular  trunk,  having  thickened  walls,  in  which,  after  a 
time,  muscular  fibre  begins  to  be  developed,  and  the  contractile  power 
manifests  itself.  The  pulsation  of  this  heart,  how^ever,  does  not 
seem  to  extend  its  influence  immediately  through  the  vascular  area-;, 
the  capillary  circulation  in  which,  remains  for  some  time  in  great 
degree  independent  of  it.  There  is  no  resemblance  in  form^  how- 
ever, between  the  dorsal  vessel  of  Insects,  and  the  incipient  heart  of 
the  higher  animals ;  since  the  latter  is  never  much  prolonged,  and 
speedily  becomes  doubled  (as  it  were)  upon  itself;  and  its  first  division 
into  distinct  cavities  is  merely  for  the  purpose  of  separating  its  receive 
ing  portion,  or  auricle,  from  its  propelling  portion,  or  ventricle.  But  the 
general  condition  of  the  Circulating  system  is  much  the  same  in  the 
two  cases ;  and  it  is  further  alike  in  this, — that  it  is  not  always  easy 
to  show  that  the  vessels  have  distinct  walls,  as  they  frequently  seem- 
like  mere  channels  excavated  in  the  tissues. 

555.  We  may  next  turn  our  attention  briefly  to  the  condition  of 
the  Circulating  apparatus  in  the  Molluscous  classes,  which  has  lately 
been  found  to  present  some  very  peculiar  characters.  In  these  it 
would  seem  as  if  the  moving  power  were  more  concentrated  in  the 
heart,  than  in  the  preceding;  for  this  organ  seems  no  longer  like  a 
mere  dilatation  of  the  vascular  trunk,  but  is  a  distinct  sac  with  musr 

21 


822  CIRCULATION  IN  MOLLUSKS. 

cular  walls,  usually  having  at  least  two  cavities,  an  auricle  and  a  ven- 
tricle. The  usual  course  of  the  circulation  is  the  following.  The 
blood,  expelled  from  the  ventricle  of  the  heart,  passes  along  the  main 
systemic  artery,  or  aorta  ;  which  distributes  it  to  the  body  at  large. 
It  is  then  collected  again,  and  transmitted  to  the  respiratory  organs ; 
in  which  it  is  exposed,  either  to  the  air  contained  in  the  surrounding 
water,  or  (in  the  terrestrial  Mollusks)  more  directly  to  the  atmosphere ; 
and  from  these  it  is  returned  to  the  heart,  to  be  again  transmitted  to 
the  system.  Thus  we  see  that  the  heart  of  these  animals  receives 
and  impels  aerated  blood  ;  and  that  its  office  is  to  send  that  blood  to 
the  capillaries  of  the  general  system.  Hence  it  may  be  called  a  5^5- 
temic  heart. 

556.  The  blood,  in  the  first  part  of  its  course,  passes  through  dis- 
tinct vessels  :  it  has  been  lately  shown,  however,  that  in  the  Mollusks 
in  general,  the  blood  which  has  passed  through  the  systemic  capilla- 
ries, and  is  on  its  way  to  the  respiratory  organs,  is  no  longer  thus 
confined,  but  that  it  meanders  through  passages  or  sinuses,  which  are 
channeled  out  in  the  tissues,  and  which  even  communicate  freely  with 
the  abdominal  cavity  in  which  the  viscera  lie  ;  so  that  their  whole 
exterior  is  bathed  by  the  circulating  fluid.  It  is  perhaps  in  this  part 
of  its  course,  that  it  most  readily  takes  up  the  fresh  nutrient  mate- 
rials, which  have  been  prepared  by  the  digestive  process,  and  which 
would,  under  such  circumstances,  find  their  way  with  comparative 
facility  from  the  inner  surface  of  their  walls  to  the  outer. — After  being 
thus  diffused,  in  its  venous  or  carbonized  state,  through  the  substance 
of  the  tissues  and  through  the  visceral  cavity,  it  is  again  collected 
into  distinct  trunks ;  and  these  convey  it  to  the  respiratory  organs. — 
Now  although  it  cannot  be  doubted,  that  the  impelling  power  of  the 
iheart  is  the  chief  cause  of  the  movement  of  the  blood  through  the  sys- 
temic vessels,  yet  it  would  seem  impossible  to  suppose,  that  this 
power  can  be  exerted  over  the  unrestrained  currents,  in  which  it  is 
diflfused  through  the  body,  after  passing  through  the  systemic  capil- 
laries ;  and  it  can  scarcely  be  doubted,  that  its  passage  through  the 
capillaries  of  the  respiratory  organs  is  due  to  the  power  which  is 
'developed  in  themselves,  under  the  conditions  already  alluded  to. 

557.  There  is  a  very  curious  phenomenon  to  be  observed  in  the 
•circulation  of  some  of  the  lowest  Mollusks;  namely,  the  continual 
.reversal  of  the  course  of  the  current.  The  heart,  in  these  animals,  is 
«nuch  less  perfectly  formed,  than  in  the  higher  tribes;  and  seems 
anore  like  the  mere  contractile  dilatation  of  the  principal  trunk,  which 
is  the  sole  representative  of  that  organ  in  the  Echinodermata.  The 
circulating  fluid  is  sometimes  transmitted  first  to  the  system  ;  and, 
after  being  distributed  to  its  different  parts  by  the  ramifications  of  the 
main  artery,  it  meanders  through  the  channels  excavated  in  its  tis- 
sues ;  and  then  flows  towards  the  respiratory  surface,  after  passing 
over  which,  it  returns  to  the  heart.  But  after  a  certain  duration  of 
its  flow  in  this  direction,  the  current  stops,  and  then  recommences  in 
the  contrary  direction, — proceeding  first  to  the  respiratory  organs,  and 


CIRCULATION  IN  FISHES. 


323 


Fig.  84. 


then  to  the  system  in  general.  It  would  seem  as  if  in  this,  one  of  the 
lowest  forms  of  animals  possessing  a  distinct  Circulation,  the  central 
power  were  not  yet  sufficiently  strong,  to  determine  the  course  which 
the  fluid  is  to  take  ;  so  that  it  undergoes  continual  vacillations.  In  a 
group  of  Compound  Polypes,  to  which  this  class  of  Mollusks  has 
many  points  of  affinity,  there  is  a  movement  of  fluid  through  the  stem 
and  branches,  which  in  like  manner  continually  changes  its  direction. 
This  movement,  however,  can  scarcely  be  regarded  in  the  light  of  a 
proper  Circulation  ;  since  the  tubes  in  which  it  occurs  are  in  direct 
communication  with  the  digestive  cavities  of  the  Polypes.  But  the 
flow  seems  altogether  independent  of  any  mechanical  propulsion  ; 
and  takes  place  most  energetically  and  regularly  towards  parts  in 
which  new  growth  is  going  on. 

558.  We  have  now  to  consider  the  chief  forms  in  which  the  Cir- 
culating apparatus  presents  itself  in  the  Vertebrated  classes  ;  and  first 
in  that  of  Fishes.  We  have  here,  as  in  Mollusks,  a  heart  with  two 
cavities,  an  auricle  and  a  ventricle  ;  this  heart,  however,  is  not  placed 
at  the  commencement  of  the  systemic  circulation,  but  at  the  origin  of 
the  respiratory  vessels.  The  blood  which  it  receives  and  propels,  is 
venous  or  carbonized  ;  this  is  transmitted  along  a  main  trunk,  which 
speedily  subdivides  into  lateral  branches  or 
arches ;  and  these  distribute  it  to  the  fringes 
of  gills,  that  hang  on  the  sides  of  the  neck. 
By  the  action  of  the  water  on  the  gills,  the 
blood  is  aerated  in  its  passage  through  them  ; 
and  it  is  then  collected  by  a  series  of  converg- 
ing vessels,  which  reunite  to  form  the  great 
systemic  artery,  or  aorta.  By  the  ramifica- 
tions of  this  artery,  the  blood,  now  aerated,  is 
distributed  through  the  system,  and  affords  the 
requisite  nourishment  and  stimulation  to  its 
tissues.  Returning  from  the  systemic  capil- 
laries in  a  venous  state,  the  blood  of  the  head 
and  anterior  portion  of  the  body  finds  its  way 
at  once  into  the  great  systemic  vein,  or  vena 
cava,  by  which  it  is  conveyed  back  to  the  au- 
ricle of  the  heart ;  but  that  which  has  traversed 
the  capillaries  of  the  posterior  part  of  the  body, 
and  of  the  abdominal  viscera,  is  conveyed  by 
a  distinct  system  of  veins  to  the  liver  and  the 
kidneys.  In  these  organs,  the  veins  again 
subdivide  into  a  network  of  capillaries,  which 
is  distributed  through  the  secreting  structure, 
and  which  serves  to  afford  to  the  secreting 
cells  the  materials.of  their  development.  This 
is  termed  the  portal  system  of  vessels.  From 
the  capillaries  of  the  liver  and  kidneys,  the  blood  is  finally  collected 
by  the  hepatic  and  renal  veins,  which  convey  it  into  the  vena  cava; 


Diagram  of  ihe  Circulating 
Apparatus  of  Fishes;— a,  the 
auricle;  &,  the  ventricle;  c, 
the  trunk  supplying  the  bran- 
chial arteries,  d,  the  aerated 
blood  returning  from  the  gills 
is  conveyed  by  e,  e,  the  bran- 
chial veins,  to  /,  the  aorta, 
which  distributes  it  to  the  sys- 
tem; thence  it  is  collected, 
and  returned  to  the  auricle, 
by  the  veins  which  unite  iu 
the  vena  cava,  g. 


324  CIRCULATION  IN  FISHES.— LANCELOT. 

where  it  is  mingled  with  the  blood  that  has  not  passed  through  those 
organs,  and  is  thus  conveyed  to  the  heart. 

559.  The  heart  of  Fishes,  then,  belongs  to  the  respiratory  circula- 
tion. It  propels  venous  blood  to  the  capillaries  of  the  gills,  in  which 
it  is  aerated ;  returning  from  these,  the  aerated  blood  is  transmitted 
through  a  second  set  of  capillaries,  those  of  the  system,  in  which  it 
again  becomes  venous  ;  whilst  a  portion  of  this  blood  is  made  to  tra- 
verse a  third  set  of  capillaries,  those  of  the  liver  and  kidneys,  before 
it  is  again  subjected  to  the  propelling  power  of  the  heart.  Now  as 
the  heart,  instead  of  being  stronger  than  it  is  in  animals  with  the  com- 
plete double  circulation  presently  to  be  described, — in  which  the 
greater  part  of  the  blood  propelled  by  it  only  traverses  one  set  of 
capillaries,  and  never  more  than  two, — is  much  weaker  in  proportion, 
it  is  evident  that  here,  too,  a  supplementary  power  must  exist,  by 
which  the  flow  of  blood  through  the  capillaries  is  aided,  and  on  which, 
indeed,  the  portal  circulation  must  greatly  depend. 

560.  It  is  requisite  that,  in  the  class  of  Fishes,  the  whole  of  the 
venous  blood  returned  from  the  system  should  pass  through  the  respi- 
ratory organs  before  being  again  transmitted  to  the  body ;  since  the 
aerating  action  of  the  small  quantity  of  air  diffused  through  the  water, 
w^ould  otherwise  be  insufficient  for  its  renovation.  But  in  Reptiles, 
all  of  which  breathe  air  during  their  adult  condition,  the  case  is  very 
different ;  for  if  the  whole  current  of  their  blood  were  exposed  to  the 
atmosphere,  before  being  again  sent  to  the  body,  the  quantity  of  oxy- 
gen conveyed  into  the  tissues  w^ould  be  too  great,  and  would  have 
an  over-stimulating  effect.  The  plan  of  the  Circulation  is,  therefore, 
differently  arranged  in  Reptiles.  We  find  the  heart  to  consist  of  three 
cavities  ;  two  auricles  and  one  ventricle.  From  the  ventricle  issues 
a  single  trunk,  which  speedily  subdivides;  some  of  its  branches  pro- 
ceeding to  the  lungs,  and  others  to  the  body.  The  blood  which  is 
transmitted  through  this  trunk,  is  of  a  mixed  character,  as  we  shall 
presently  see  ;  being  neither  fully  aerated,  nor  yet  highly  carbonized. 
It  contains  sufficient  oxygen,  to  stimulate  the  nervous  and  muscular 
systems  of  these  comparatively  inert  animals ;  whilst  it  also  contains 
enough  of  carbonic  acid,  to  require  being  exposed  to  the  atmosphere 
through  the  medium  of  the  lungs.  The  blood  which  has  passed 
through  the  systemic  capillaries,  and  which  has  been  thereby  ren- 
dered completely  venous,  is  returned  to  one  of  the  auricles — the 
systemic — by  the  vena  cava.  On  the  other  hand,  the  blood  which 
has  passed  through  the  capillaries  of  the  lungs,  and  which  has 
been  thereby  rendered  completely  arterial,  is  returned  through  the 
pulmonary  vein  to  the  other  auricle, — the  pulmonary.  Thus  one 
of  the  auricles  exclusively  receives  aerated,  and  the  other  carbonated 
blood  ;  and  as  both  pour  their  contents  into  the  common  ventricle, 
the  blood  which  that  cavity  contains  and  propels  ;s  of  a  mixed  cha- 
racter. 

561.  An  extremely  interesting  aspect  of  the  circulating  apparatus 
is  presented  by  the  Amphioxus  or  Lancelot ;  an  animal  which  presents 


I 


CIRCULATION  IN  REPTILES.  325 

the  general  form  of  a  Fish,  and  which  can  scarcely  be  referred  to  any- 
other  group  ;  but  in  which  the  characters  of  the  Vertebrated  series  are 
degraded  (as  it  were)  to  the  level  of  the  lowest  Molluscous  and  Ver- 
miform classes.  The  blood,  which  is  white,  moves  through  distinct 
vessels,  but  there  is  no  proper  heart ;  and  the  vascular  trunks  present 
several  dilatations,  in  different  parts,  which  have  muscular  walls, 
and  show  contractile  power.  Thus  the  circulation  is  carried  on,  not 
through  the  agency  of  a  central  impelling  organ,  as  in  Fishes ;  but 
by  power  which  is  scattered  or  diffused  through  various  parts  of  the 
system  of  blood-vessels,  as  in  the  lower  Invertebrata. — The  respira- 
tory apparatus,  also,  is  formed  upon  a  type  much  lower  than  that  of 
Fishes ;  for  it  consists  simply  of  a  dilatation  of  the  first  part  of  the 
alimentary  canal,  or  pharynx,  upon  the  walls  of  which  the  blood  is 
distributed  in  divided  streams,  its  cavity  being  filled  with  water, 
which  serves  to  aerate  the  blood.  This  is  precisely  the  type,  on 
which  the  respiration  is  eflfected,  in  those  lowest  Mollusks,  of  which 
mention  has  just  been  made,  as  exhibiting  alternations  in  the  direction 
of  the  circulating  current  (§  557).  In  other  respects,  however,  the 
arrangement  of  the  vascular  system  in  this  extraordinary  animal,  cor- 
responds with  that  which  obtains  in  Fishes. 

562.  Various  modifications  of  this  form  of  Circulating  apparatus 
exist  in  the  different  groups  of  Reptiles.  In  the  lowest  among  them, 
which  breathe  permanently  by  gills  like  Fishes,  besides  possessing 
imperfectly  developed  lungs,  the  apparatus  exhibits  a  blending  of 
both  plans;  for  a  small  portion  of  the  blood,  which  is  propelled  by 
each  contraction  of  the  ventricle,  passes  directly  to  the  lungs;  the 
principal  part  of  it  being  at  once  distributed  to  the  gills  as  in  Fishes. 
After  passing  through  these,  it  is  transmitted  to  the  general  system ; 
and  on  returning  thence,  in  a  completely  venous  state,  it  is  mingled 
with  the  blood  which  has  been  arterialized  in  the  lungs.  This  latter, 
however,  bears  so  small  a  proportion  to  the  rest,  that,  if  the  aeration 
were  not  partly  effected  by  the  gills,  it  would  be  insufficient  for  the 
wants  of  the  animal. — The  tadpoles  of  the  common  Frog  and  Water 
Newt,  as  well  as  of  other  species  which,  like  them,  begin  life  in  the 
general  condition  of  Fish,  present  a  similar  condition  at  one  period 
of  their  change.  At  first,  the  whole  aeration  is  effected  by  means  of 
gills,  the  lungs  being  in  a  rudimentary  or  undeveloped  state ;  and  the 
entire  circulation  is  carried  on  as  in  Fishes,  the  pulmonary  vessels 
being  scarcely  traceable.  As  the  lungs  begin  to  be  developed,  how- 
ever, a  portion  of  the  blood  is  sent  to  them ;  and  at  the  same  time, 
communicating  passages  which  previously  existed,  between  the  ves- 
sels that  convey  blood  to  the  gills,  and  those  that  return  it  from  them, 
are  increased  in  size ;  so  that  a  certain  proportion  of  the  blood  is  trans- 
mitted to  the  system,  without  having  passed  through  the  gills  at  all. 
By  a  further  increase  in  the  diameter  of  these,  the  whole  current  of 
blood  takes  this  direction,  the  gills  being  no  longer  serviceable ;  and 
as,  at  the  same  time,  the  lungs  are  attaining  their  full  development, 
the  aeration  which  they  effect  in  the  blood  transmitted  to  them  be- 


326 


CIRCULATION  IN  MAMMALS. 


Fig.  85. 


comes  sufficient,  and  the  whole  circulation  is  thus  permanently  estab- 
lished on  the  Reptile  type. 

563.  On  the  other  hand,  among  the 
higher  Reptiles,  we  find  the  circulating  ap- 
paratus presenting  approaches  to  the  form 
it  possesses  in  Birds  and  Mammals.  For 
the  ventricle  is  divided,  more  or  less  com- 
pletely, into  two  cavities,  one  of  which 
propels  aerated  blood  to  the  system,  whilst 
the  other  transmits  venous  blood  to  the 
lungs.  A  certain  amount  of  mixture  of 
arterial  and  venous  blood  always  takes 
place,  however,  either  in  the  heart  itself, 
or  in  the  vessels  ;  so  that  the  blood  which 
the  body  receives  is  never  purely  arterial. 
But  this  mixture  is  sometimes  effected  in 
such  a  manner,  that  pure  arterial  blood  is 
sent  to  the  head  and  anterior  extremities ; 
though  the  remainder  of  the  body  receives 
a  half-aerated  fluid.  This  is  accomplished 
in  the  Crocodile,  by  a  provision  very  simi- 
lar to  that  which  exists  in  the  foetus  of 
warm-blooded  animals  (Chap.  XI).  The 
portal  circulation  in  Reptiles  is  carried  on 
nearly  upon  the  same  plan  as  in  Fishes.  It 
receives  the  blood  from  the  posterior  ex- 
tremities and  from  the  tail,  as  well  as  from  the  abdominal  viscera ; 
and  this  blood  is  distributed  by  the  portal  capillaries,  not  only  through 
the  liver,  but  also  through  the  kidneys,  although  the  latter  also  receive 
arterial  branches  from  the  aorta.  The  fact  that  the  kidneys  are  sup- 
plied from  the  general  portal  circulation,  in  Fishes  and  Reptiles,  has 
an  important  bearing  on  the  difference  in  the  arrangement  of  their 
own  vessels,  which  will  be  hereafter  shown  to  exist,  between  the  kid- 
neys of  these  animals,  and  those  of  Birds  and  Mammals  (§  727). 

564.  In  the  warm-blooded  division  of  the  Vertebrated  series,  which 
includes  the  classes  of  Birds  and  Mammals,  we  find  the  whole  circu- 
lation possessed  of  a  greatly  increased  energy ;  but  the  distinguishing 
peculiarity  of  the  apparatus  in  these  animals,  is  that  conformation  of 
the  heart  and  vessels,  which  secures  a  complete  double  circulation  of 
the  blood ;— that  is,  which  provides  for  the  aeration  of  every  particle 
of  the  venous  blood  which  has  returned  from  the  system,  before  it  is 
again  sent  into  the  tissues.  The  heart  may  be  regarded  as  consisting 
of  two  distinct  parts, — a  systemic  heart,  like  that  of  the  MoUusks, 
forming  its  left  side, — and  a  respiratory  heart,  like  that  of  Fishes, 
constituting  its  right.  Each  of  these  parts  has  a  receiving  cavity  or 
auricle,  and  an  impelling  cavity  or  ventricle.  The  cavities  of  the 
two  sides  are  completely  separated  from  one  another,  in  the  adult 
state  at  least ;  though  their  walls  are  united,  for  economy  of  material. 


Diagram  of  the  Circulation  in 
Reptiles : — a,  single  ventricle,  re- 
ceiving the  aerated  blood  from  6, 
the  pulmonary  auricle,  and  venous 
blood  from  c,  the  systemic  auricle; 
and  propelling  part  of  this  mixed 
fluid  to  the  pulmonary  capillaries 
d,  and  part  to  the  systemic  capil- 
laries, e. 


CIRCULATION  IN  MAMMALS. 


327 


Fig.  86. 


It  is  obvious  that  much  is  saved  in  this  manner  ;  since,  as  the  con 
tractions  of  the  auricles  and  of  the  ven- 
tricles on  the  two  sides  occur  simultane- 
ously, the  pressure  of  blood  in  the  one  is 
partly  antagonized  by  that  on  the  other, 
wherever  it  acts  on  the  wall  that  is  com- 
mon to  both.  This  antagonism  is  not 
complete,  however  ;  since  the  systemic 
ventricle  contracts  with  far  greater  force 
than  the  pulmonary ;  and  the  wall  be- 
tween them  must  be  capable  of  resisting 
the  difference  of  pressure  on  its  two 
sides  thus  occasioned. — The  blood  which 
is  returned  from  the  system,  in  a  venous 
state,  through  the  vena  cava  to  the  right 
auricle,  and  which  is  poured  by  it  into 
the  right  ventricle,  is  impelled  by  the 
latter  through  the  capillaries  of  the  lungs, 
where  it  undergoes  aeration.  Returning 
thence,  in  an  arterialized  state,  it  is  con- 
veyed into  the  left  auricle,  and  thence 
flows  into  the  left  ventricle  ;  by  which  it 
is  propelled  through  the  great  systemic 
artery  or  aorta,  and  through  its  ramifica- 
tions to  the  general  system. 

565.  The  greater  part  of  the  blood, 
which  has  been  rendered  venous  by  pas- 
sing through  the  systemic  capillaries,is  col- 
lected bythe  systemic  veins,  and  is  returned  directly  to  the  heart  through 
the  vena  cava.  But  a  portion  is  still  employed  for  the  distinct  circula- 
tion, which  is  destined  to  supply  the  materials  for  the  secreting  action 
of  the  liver.  The  blood  that  has  traversed  the  capillaries  of  the  walls 
of  the  alimentary  canal,  and  of  the  other  viscera  concerned  in  diges- 
tion, is  collected  again  by  the  converging  veins  into  a  large  venous 
trunk,  the  vena  portee,  by  which  it  is  distributed  through  the  liver. 
This  vessel,  although  formed  by  the  convergence  of  veins,  and  con- 
veying venous  blood,  has  really  the  character  of  an  artery  in  an  equal 
degree ;  for  it  subdivides  and  ramifies  after  its  entrance  into  the  liver, 
so  as  to  form  a  network  of  capillaries,  from  which  the  blood  is  again 
collected,  and  thence  transmitted  by  the  hepatic  vein  to  the  vena  cava. 
— Thus  that  portion  of  blood,  which  supplies  the  liver  with  the  mate- 
rials of  its  secreting  action,  passes  through  two  sets  of  capillaries, 
between  the  time  of  its  leaving  the  heart  and  its  return  to  it.  The 
portal  circulation  in  Birds,  as  in  Reptiles  and  Fishes,  receives  the 
blood  from  the  posterior  part  of  the  body,  and  from  the  extremities ; 
but  the  portal  blood  is  only  conveyed  to  the  liver;  the  kidneys  being 
supplied  by  the  renal  arterv. 


Diagram  of  the  Circulating  Ap- 
paratus in  Mammals  and  Birds  : — a, 
the  heart  containing  four  cavities ;  b, 
vena  cava,  delivering  venous  blooa 
into  c,  the  right  auricle ;  d,  the  right 
ventricle,  propelling  venous  blood 
through  e,  the  pulmonary  artery,  to/, 
the  capillaries  of  the  lungs ;  g,  the 
left  auricle,  receiving  the  agrated 
blood  from  the  pulmonary  vein,  and 
delivering  it  to  the  left  ventricle,  h, 
which  propels  it  through  the  aorta  i,  to 
the  systemic  capillaries,  j,  whence 
It  is  collected  by  the  veins,  and  car- 
ried back  to  the  heart  through  the 
vena  cava,  b. 


328 


CIRCULATION  IN  MAMMALS.  ^ 

Fig.  87. 


Anatomy  of  the  human  heart  and  lungs.  1.  The  right  ventricle ;  the  vessels  to  the  right  of  the 
figure  are  the  middle  coronary  artery  and  veins  ;  and  those  to  its  left,  the  anterior  coronary  artery  and 
veins.  2.  The  left  ventricle.  3.  The  right  auricle.  4.  The  left  auricle.  5.  The  pulmonary  artery. 
6.  The  right  pulmonary  artery.  7.  The  left  pulmonary  artery.  8.  The  remains  of  the  ductus  arte- 
riosus 9.  The  arch  of  the  aorta.  10.  The  superior  vena  cava.  11.  The  right  arteria  innominata, 
and  in  front  of  it  the  vena  innominata.  12.  The  right  subclavian  vein,  and  behind  it  its  corresponding 
artery.  13.  The  right  common  carotid  artery  and  vein.  14  The  left  vena  innominata.  1.5.  The  left 
carotid  artery  and  vein.  16  The  left  subclavian  vein  and  artery.  17.  The  trachea.  15.  The  right 
bronchus.  19.  The  left  bronchus.  20,20.  The  pulmonary  veins;  18,20,  form  the  root  of  the  right 
lung;  and,  7, 19.  20,  the  root  of  the  left.  21.  The  superior  lobe  of  the  right  lung.  22.  Its  middle  lobe. 
23.  Its  inferior  lobe.    24.  The  superior  lobe  of  the  left  lung.    25.  Its  inferior  lobe. 

566.  This  perfect  form  of  the  Circulating  apparatus  is  only  attained, 
in  the  warm-blood  animal,  after  a  series  of  transformations,  which 
strongly  remind  us  of  the  permanent  forms  presented  by  the  vascular 
system  in  Fishes  and  Reptiles.  Thus  in  the  embryo  of  the  Chick  at 
about  the  60th  hour,  and  in  that  of  the  Dog  at  about  the  21st  day, 
the  curved  and  dilated  tube,  of  which  the  heart  previously  consisted, 
(§  554,)  is  found  to  be  distinctly  divided  into  an  auricle  and  a  ven- 
tricle. From  the  latter  originates  the  main  arterial  trunk,  which 
divides  into  four  pairs  of  lateral  branches;  and  these  pass  round  the 
pharynx  precisely  in  the  position  and  direction  of  the  arteries  of  the 
gills  of  Fishes.  They  do  not,  however,  distribute  the  blood  to  gill- 
tufts;  for  none  such  are  developed  in  the  embryo  of  the  warm-blooded 
ainimal;  but  they  meet  again  below  the  pharynx,  to  form  a  trunk, 
•which  supplies  the  general  circulation. — Within  a  short  period,  how- 
ever, the  whole  plan  of  the  circulation  undergoes  a  change.  The 
auricle  and  the  ventricle  are  each  divided  by  a  partition,  that  is  de- 
veloped in  the  middle  of  the  heart ;  and  thus  the  two  auricles  and  the 
two  ventricles  are  formed.  Whilst  this  is  going  on,  a  change  takes 
place  also  in  the  vessels  that  arise  from  the  heart;  for  the  arterial 
trunk,  that  was  previously  single,  undergoes  a  division  into  two  dis- 
tinct tubes;  one  of  which  is  connected  with  the  left  ventricle,  and 


MOVING  POWERS  OF  THE  CIRCULATION.  329 

becomes  the  aorta,  whilst  the  other  originates  in  the  right  ventricle, 
and  becomes  the  pulmonary  artery.  Of  the  four  pairs  of  branchial 
arches,  some  are  subsequently  obliterated  ;  whilst  others  undergo 
changes  that  end  in  their  becoming  the  arch  of  the  aorta,  the  right 
and  left  pulmonary  arteries,  and  the  right  and  left  subclavians. 

567.  The  muscular  power  of  the  heart  is  much  greater  in  the  warm- 
blooded than  in  the  cold-blooded  Vertebrata,  in  proportion  to  the 
extent  of  the  circulation  which  it  is  concerned  in  maintaining ;  and 
it  is  evidently  destined  to  take  a  much  larger  share  in  the  propulsion 
of  the  fluid,  than  it  is  in  the  lower  tribes.  Many  Physiologists,  indeed, 
are  of  opinion  that  the  movement  of  the  blood  is  entirely  due  to  the 
action  of  the  heart;  and  this  view  appears  to  be  supported  by  the 
results  of  numerous  experiments  upon  the  circulation.  But  it  is  very 
difficult,  if  not  impossible,  to  make  experiments  that  shall  be  really 
satisfactory  upon  this  point ;  and  it  appears  safer  to  trust  to  the  "  expe- 
riments ready  prepared  for  us  by  Nature,"  as  Cuvier  termed  them, — 
namely,  those  lower  forms  of  animated  being,  in  which  various  diver- 
sities of  structure  present  themselves,  and  in  which  we  can  study  the 
regular  and  undisturbed  effects  of  these. — Thus  we  have  seen  that, 
in  Plants  and  the  lowest  Animals,  which  have  no  central  impelling 
cavity,  the  movement  of  the  nutritive  fluid  is  entirely  dependent  upon 
the  power  that  is  diffused  through  the  network  of  vessels  in  which  it 
circulates.  As  we  ascend  the  series,  we  find  an  organ  of  impulsion 
developed  upon  a  certain  part  of  the  vascular  system,  whose  object 
it  is  to  give  increased  energy  and  regularity  to  the  movement.  And 
ascending  still  higher,  we  find  the  moving  power  gradually  con- 
centrated, as  it  were,  in  this  organ ;  yet  it  is  not  altogether  with- 
drawn from  the  capillary  network,  as  we  shall  see  from  several  facts 
to  be  presently  adduced.  The  particular  actions  of  the  Heart,  the 
Arteries,  the  Capillaries,  and  the  Veins,  will  now  be  considered  in 
more  detail. 

3.  Action  of  the  Heart, 

568.  The  Heart  is  a  hollow  muscle,  endowed  in  an  eminent  degree 
with  the  property  of  irritability  ;  by  which  is  meant,  the  capability  of 
being  easily  excited  to  movements  of  contraction  alternating  with  re- 
laxation (§  347).  At  first  sight,  its  actions  seem  different  from  that 
of  the  muscles,  which  are  called  into  action  by  the  impulse  of  the  will ; 
for  in  these  there  is  apparently  no  such  alternation,  the  state  of  con- 
traction being  kept  up  as  long  as  the  will  operates.  But  it  has  been 
already  explained  that,  even  in  these,  the  individual  fibres  are  proba- 
bly in  a  state  of  continual  alternation  of  contraction  and  relaxation, 
during  their  active  condition, — one  set  taking  up  the  action,  whilst 
another  is  returning  to  the  state  of  relaxation.  Hence  the  chief  pecu- 
liarity in  the  Heart's  action  consists  in  this, — that  the  whole  mass  of 
fibres  of  each  division  of  the  organ  contract  and  relax  together.  The 
contraction  of  the  two  ventricles  is  perfectly  synchronous,  as  is  that  of 


330  MOVEMENTS  OF  THE  HEART. 

the  two  auricles ;  but  the  contraction  of  the  auricles  is  synchronous 
•with  the  dilatation  of  the  ventricles,  and  vice  versa.  The  regularity 
of  this  alternation,  however,  is  somewhat  disturbed,  when  the  irrita- 
bility of  the  heart  is  becoming  exhausted  ;  and  both  sets  of  movements 
will  continue,  when  the  auricle  and  ventricle  have  been  separated 
from  one  another.  Their  regular  succession,  in  the  natural  state,  is 
doubtless  in  part  due  to  the  fact,  that  the  transmission  of  blood  from 
the  auricle  into  the  ventricle,  by  the  contraction  of  the  former,  is  the 
stimulus  which  most  effectually  excites  the  latter  to  contraction  ;  whilst 
the  ventricle  is  contracting,  the  auricle,  now  free  to  dilate,  is  distended 
by  the  flow  of  blood  from  the  veins  that  open  into  it ;  and  this  flow 
stimulates  it  to  renewed  contraction,  just  at  the  time  when  the  con- 
traction of  the  ventricle  has  been  completed,  and  its  state  of  relaxa- 
tion enables  it  to  receive  the  blood  poured  in  through  the  orifice  lead- 
ing from  the  auricles. 

569.  In  the  living  animal,  the  auricular  and  ventricular  movements 
succeed  one  another  with  great  regularity ;  and  when  the  circulation 
is  proceeding  with  vigour,  scarcely  any  appreciable  pause  can  be  dis- 
covered between  the  different  acts.  The  contraction  or  systole  of  the 
Auricle  takes  place  precisely  at  the  same  moment  w^th  the  dilatation 
or  diastole  of  the  Ventricles;  and,  as  soon  as  the  latter  are  full,  and 
the  former  are  empty,  the  diastole  of  the  Auricles,  and  the  systole  of 
the  Ventricles,  immediately  succeed.  The  systole  of  the  Ventricles 
occasions  the  propulsion  of  blood  into  the  arterial  system ;  and  this 
action  produces  the  pulse,  as  will  be  explained  hereafter.  And  it  also 
corresponds  with  the  impulse  or  stroke  of  the  heart  against  the  parietes 
of  the  chest.  This  impulse  is  not  produced,  as  some  have  supposed, 
by  the  swinging  of  the  entire  heart  forwards ;  but  by  the  peculiar 
mode  in  which  the  Ventricular  systole  takes  place.  In  the  contraction 
of  its  walls,  every  dimension  is  lessened  ;  but  shortening  is  the  most 
perceptible  change,  the  vertical  diameter  of  the  Ventricle  being  the 
greatest.  Owing  to  the  peculiar  spiral  disposition  of  the  fibres  of  the 
heart,  its  apex  is  not  simply  drawn  upwards  by  their  contraction,  but 
it  is  made  to  describe  a  spiral  movement,  from  right  to  left,  and  from 
behind  forwards ;  and  it  is  in  this  manner,  that  it  is  caused  to  strike 
against  the  side  of  the  chest. 

570.  The  systole  of  the  Ventricles  is  immediately  followed  by  their 
diastole  ;  but  the  commencement  of  this  has  been  observed  to  occur 
at  a  small  interval  previous  to  the  contraction  of  the  Auricles ;  and 
sometimes  a  brief  interval  of  repose  may  be  noticed,  separating  the 

Jirst  stage  of  the  Ventricular  diastole,  which  may  be  partily  due  to  the 
simple  elasticity  of  the  walls  of  the  Ventricles,  from  the  second,  which 
is  accompanied  by  the  systole  of  the  Auricles,  and  in  which  the  blood 
of  the  latter  is  forcibly  propelled  into  them.  When  the  circulation  is 
being  carried  on  regularly,  the  blood  is  propelled  into  the  Ventricles 
with  sufficient  force  to  dilate  them  strongly ;  so  that  the  hand  closed 
upon  the  heart  is  opened  with  violence.  Even  the  auricles  dilate 
with  more  force  than  it  seems  easy  to  account  for  by  the  vis  a  tergo 


MOVEMENTS  AND  SOUNDS  OF  THE  HEART.  331 

of  the  blood  in  the  venous  system ;  which  is  small  compared  with 
that  which  the  fluid  possesses  in  the  arteries. 

571.  The  natural  movements  of  the  Heart  are  accompanied  by  cer- 
tain sounds,  which  are  heard  when  the  ear  is  applied  over  the  cardiac 
region ;  and  an  acquaintance  with  these  sounds  and  with  their  causes 
is  of  much  importance,  since  the  alterations  which  they  undergo  in 
disease,  afford  us  some  of  our  most  accurate  information  in  regard  to 
the  nature  of  the  morbid  affection.  Concurrently  with  the  impulse  of 
the  heart  against  the  chest,  a  dull  and  prolonged  sound  is  heard  ;  this, 
which  is  termed  the  Jirst  sound,  marks  the  ventricular  systole,  and  is 
synchronous  with  the  pulsation  in  the  arteries.  The  second  sound, 
which  is  short  and  sharp,  follows  immediately  upon  the  conclusion  of 
the  first;  and  it  must  therefore  be  produced  during  the  first  stage  of 
the  Ventricular  diastole,  before  the  systole  of  the  Auricles  has  com- 
menced. It  is  followed  by  a  brief  interval  of  repose,  which  occurs 
during  the  remainder  of  the  Ventricular  diastole  and  the  Auricular 
systole ;  and  this  is  succeeded  by  a  recurrence  of  the  first  sound.  If 
the  whole  period  between  two  successive  pulsations  be  divided  into 
four  parts,  it  is  estimated  that  the  first  sound  usually  occupies  two  of 
these ;  and  the  second  sound,  and  the  interval,  one  part  each. 

572.  Now  in  order  to  understand  the  causes  of  these  sounds,  it  is 
necessary  to  study  the  course  of  the  blood  through  the  heart  a  little 
more  in  detail.  When  the  Ventricles,  distended  with  blood,  are  con- 
tracting upon  their  contents,  they  eject  them  forcibly  through  the  nar- 
row orifices  of  the  aorta  and  pulmonary  artery;  and  the  semilunar 
valves,  which  guard  these  orifices,  are  thrown  back  against  the  walls 
of  the  arteries.  The  regurgitation  of  the  blood  into  the  auricles  is 
prevented  by  the  action  of  the  mitral  and  tricuspid  valves ;  but  the 
flaps  of  these  do  not  suddenly  fall  against  each  other,  when  the  blood 
first  begins  to  press  them  together ;  being  restrained  by  the  chorda 
tendinece.  The  connection  of  these  with  the  carnecu  columncB,  which 
form  part  of  the  ventricular  walls,  and  contract  simultaneously  with 
them,  appears  to  have  this  use  : — that  the  flaps  of  the  valves,  which 
are  completely  thrown  back  during  the  preceding  rush  of  blood  from 
the  auricles  to  the  ventricles,  may  be  drawn  into  a  favourable  posi- 
tion, for  the  blood  to  get  behind  them  and  bring  them  together,  so  as 
completely  to  close  the  orifice.  As  soon  as  the  ventricular  diastole 
begins  to  take  place  (even  before  the  contraction  of  the  auricles  has 
commenced)  there  will  be  a  tendency  of  the  blood,  that  has  just  been 
propelled  into  the  aorta  and  pulmonary  artery,  to  flow  back  to  the 
heart ;  but  this  regurgitation  is  completely  prevented  by  the  semilu- 
nar valves  of  these  orifices,  which  are  immediately  filled  out  by  this 
backward  tendency  of  the  blood,  and  which  meet  in  such  a  manner 
as  completely  to  close  the  orifices.  This  closure  is  much  more  sudden 
than  that  of  the  mitral  and  tricuspid  valves,  being  altogether  unre- 
strained. 

573.  The^rs^  sound  is  certainly  in  part  due  to  the  impulse  of  the 
heart  against  the  thoracic  parietes ;  as  is  proved  by  the  fact,  that  when 


332  SOUNDS  OF  THE  HEART. 

the  impulse  is  prevented,  the  sound  is  much  diminished  in  intensity ; 
and  also  by  the  circumstance,  that,  when  the  ventricles  contract  with 
vigour,  the  greatest  intensity  of  the  sound  is  over  the  point  of  percus- 
sion. But  that  it  is  not  entirely  due  to  this  cause,  is  also  sufficiently 
evident  from  two  circumstances ; — its  prolonged  character,  which 
could  scarcely  be  given  by  a  momentary  impulse  ; — and  its  continu- 
ance, though  with  diminished  intensity,  when  the  parietes  of  the 
chest  are  wanting,  and  even  after  the  complete  removal  of  the  heart 
from  the  body.  Moreover,  the  duration  of  the  first  sound  is  much 
increased  by  any  morbid  state  of  the  orifices  of  the  ventricles,  which 
obstructs  the  exit  of  the  blood.  Much  discussion  has  taken  place  as 
to  the  cause  of  that  part  of  it,  which  is  not  due  to  the  impulse ;  some 
having  attributed  it  to  the  muscular  contraction  of  the  walls  of  the 
ventricles,  others  to  the  flow  of  blood  over  the  irregular  surfaces  of 
their  interior,  and  others  to  the  rush  of  the  fluid  through  the  narrow 
orifices  leading  to  the  aorta  and  pulmonary  artery.  There  can  be  little 
doubt,  that  the  first  and  last  of  these  causes  are  both  concerned  in 
producing  the  sound.  For  as  a  sound  may  be  distinctly  heard  by 
means  of  the  stethoscope,  when  the  heart  is  contracting  vigorously 
out  of  the  body,  and  when  no  blood  is  propelled  by  it,  nothing  else 
than  muscular  contraction  can  be  then  regarded  as  its  source ;  and 
there  is  other  evidence  that  sound  may  be  produced  by  this  cause, 
since  the  vigorous  contraction  of  any  other  large  muscle  gives  rise  to 
a  continued  tingling,  which  may  be  heard  through  the  stethoscope. 
But  when  the  heart  is  contracting  in  its  natural  position,  and  is  pro- 
pelling the  blood  with  its  ordinary  vigour,  the  sound  is  heard  in  its 
greatest  intensity  at  the  base  of  the  heart,  i.e.,  at  the  origin  of  the 
great  arteries ;  and  since  any  obstruction  to  the  exit  of  the  blood 
through  them  increases  the  intensity,  as  well  as  the  length  of  the 
sound,  it  can  scarcely  be  doubted  that  it  is  partly  due  to  the  rush  of 
the  blood  through  the  contracted  entrances  of  these  vessels.  A  very 
similar  sound,  known  as  the  "  bruit  de  soufflet,"  or  bellows-sound, 
may  be  heard  through  the  stethoscope,  over  any  large  artery,  when  it 
is  compressed,  so  as  to  permit  the  passage  of  blood  less  readily  than 
usual.  Thus  the  ordinary  first  sound  may  be  regarded  as  composite 
in  its  nature  ;  being  made  up  of  the  sound  produced  by  the  impulse 
of  the  heart  against  the  parietes  of  the  chest,  of  the  muscular  sound 
occasioned  by  the  forcible  contraction  of  the  thick  walls  of  the  ven- 
tricles, and  of  the  sound  generated  by  the  friction  of  the  particles  of 
blood  against  each  other,  and  against  the  boundaries  of  the  narrowing 
orifices  which  lead  into  the  vessels. 

574.  The  cause  of  the  second  sound  is  simpler,  and  more  easily 
understood.  It  is  due  to  the  sudden  filling-out  of  the  semilunar  valves 
with  blood,  ^t  the  moment  when  the  ventricular  systole  has  ceased, 
and  when  the  commencing  diastole  produces  a  tendency  to  the  regur- 
gitation of  blood  from  the  aorta  and  pulmonary  artery.  The  sudden 
passage  of  the  valves,  from  a  state  of  complete  relaxation  to  one  of 
complete  tension,  occasions  a  sort  of  c/icA:;  which  is  the  second  sound 


SOUNDS  OF  THE  HEART— THICKNESS  OF  ITS  WALLS.  333 

of  the  heart.  That  this  is  the  real  cause,  has  now  been  fully  demon- 
strated. If  one  of  the  valves  be  hooked  back  against  the  side  of  the 
artery,  by  the  introduction  of  a  curved  needle,  so  that  a  reflux  of 
blood  is  permitted,  the  sound  is  entirely  suppressed.  And  if  the 
complete  closure  of  the  valves  be  prevented  by  disease,  so  that  their 
tension  is  diminished,  and  a  certain  amount  of  regurgitation  takes 
place,  the  second  sound  is  no  longer  heard  in  its  proper  intensity; 
whilst,  on  the  other  hand,  a  sound  analogous  to  the  first,  and  some- 
times prolonged  over  the  whole  interval  of  repose,  indicates  the  reflux 
of  the  blood  into  the  ventricles.  When  the  semilunar  valves  are 
thickened  by  morbid  deposit,  their  surface  roughened,  and  their  open- 
ing narrowed,  the  first  sound  becomes  harsher  and  sharper;  and  the 
second  sound  acquires  the  same  character, — the  backward  as  well  as 
the  forward  flow  of  the  blood  being  affected  by  this  cause. 

575.  The  natural  movements  of  the  mitral  and  tricuspid  valves  ap- 
pear to  be  accomplished  with  perfect  freedom  from  sound  ;  for  the  size 
of  the  orifices  which  they  guard  prevents  any  considerable  friction  of 
the  blood,  in  its  flow  from  one  cavity  to  the  other;  and  their  closure, 
when  the  ventricular  systole  begins,  does  not  take  place  with  the 
rapidity  and  suddenness  of  that  of  the  semilunar  valves.  But  w^hen 
their  structure  is  changed  by  disease,  their  action  is  not  so  noiseless; 
and  they  give  rise  to  various  morbid  sounds,  which  are  heard  in  addi- 
tion to  the  ordinary  sounds,  and  which  may  even  obscure  them  alto- 
gether— In  the  same  manner  the  ordinary  movements  of  the  heart  do 
not  produce  any  audible  friction  sound,  between  the  two  surfaces  of 
the  pericardium,  that  which  covers  the  heart  and  that  which  lines  the 
pericardial  sac.  These  surfaces  are  kept  moist,  in  health,  by  the  serous 
fluid  constantly  exhaling  from  them ;  and  they  are  extremely  smooth ; 
so  that  they  glide  over  one  another  noiselessly.  But  if  they  become 
dry,  as  in  the  first  stage  of  inflammation,  a  slight  creaking  is  heard, 
accompanying  both  the  ordinary  sounds  of  the  heart,  and  somewhat 
resembling  the  rustling  of  paper.  And  if  they  are  roughened  by  the 
deposit  of  inflammatory  exudations,  this  **  to  and  fro"  sound  becomes 
of  a  harsher  character. 

576.  The  walls  of  the  left  Ventricle  are  considerably  thicker  than 
those  of  the  right ;  and  the  contractile  power  is  greater.  This  diflfer- 
ence  is  obviously  required,  by  the  diflference  in  length  between  the 
systemic  and  the  pulmonary  vessels;  the  amount  of  force  necessary  to 
drive  the  blood  through  the  latter  being  far  inferior  to  that  which  is 
requisite  to  propel  it  through  the  former.  The  average  thickness  of  the 
walls  of  the  left  Ventricle  is  about  A\  lines;  being  somewhat  greater 
than  this  at  the  middle  of  the  heart,  and  less  at  its  apex.  The  average 
thickness  of  the  walls  of  the  right  ventricle  is  not  more  than  1 J  line ; 
being  a  little  greater  than  this  at  the  base,  and  less  at  the  apex  of  the 
heart.  The  left  auricle  is  somewhat  thicker  than  the  right. — The  ca- 
pacities of  all  the  four  cavities  are  nearly  equal;  each  of  them,  in  the 
full-sized  heart,  holding  about  two  ounces  of  fluid.  The  Ventricles 
are,  perhaps,  a  little  larger  than  their  respective  Auricles;  but  there 


334  RATE  OF  CIRCULATION. 

is  no  very  positive  difference  in  capacity,  between  the  Ventricles  and 
Auricles  of  the  two  sides. 

577.  The  quantity  of  blood  which  is  propelled  at  each  Ventricular 
systole,  cannot,  therefore,  exceed  two  ounces;  and  it  is  probably 
somewhat  less,  as  the  ventricles  do  not  seem  to  empty  themselves 
completely  at  each  contraction.  Now  the  whole  quantity  of  the  blood 
seems  to  be  about  one-fifth  of  the  entire  weight  of  the  body ;  so  that 
it  will  amount  to  about  28  lbs.  in  an  individual  of  140  lbs.  weight. 
Allowing  75  pulsations  to  a  minute,  150  ozs.  (or  91bs.  6  ozs.)  of 
blood  would  pass  through  each  ventricle  of  the  heart  in  that  time ; 
consequently  nearly  three  minutes  would  be  required  for  the  passage 
of  the  entire  mass  of  the  blood  through  the  whole  circle  of  its  move- 
ment, if  its  rate  be  entirely  determined  by  the  impulses  it  receives 
from  this  central  organ. — But  it  appears,  from  various  experiments, 
that  the  rate  of  circulation  is  much  more  rapid  than  this.  For  if  a 
solution  of  any  salt  easily  detectible  in  the  blood,  be  injected  into 
one  of  the  large  veins  near  the  heart,  it  may  be  traced  in  the  arterial 
circulation  in  from  15  to  20  seconds  afterwards;  during  which  inter- 
val it  must  have  traversed  the  whole  pulmonary  system  of  vessels 
and  passed  through  both  sides  of  the  heart.  And  if  the  salt  be  one 
which  acts  powerfully  on  the  heart  itself, — as  is  the  case  with  Nitrate 
of  Baryta  or  Nitrate  of  Potass, — this  action  is  manifested  almost  at 
the  same  moment  with  the  appearance  of  the  salt  in  the  arteries  of 
other  parts ;  thus  showing  that  it  has  been  conveyed  by  the  coronary 
arteries  into  the  capillaries  of  the  heart  itself.  The  period  required 
for  the  transmission  of  a  saline  substance  from  the  veins  of  the  upper 
part  of  the  body  to  those  of  the  lower, — which  can  scarcely  be  accom- 
plished through  any  more  direct  channel  than  the  current  that  returns 
to  the  heart,  then  passes  through  the  lungs  back  to  the  heart  again,  and 
then  flows  through  the  systemic  arteries  and  capillaries  to  the  veins, — is 
accomplished  in  little  more  than  20  seconds,  even  in  an  animal  so  large 
as  a  Horse.  It  appears,  then,  that  even  the  vigorous  and  constant 
action  of  the  Heart  is  not  alone  sufficient  to  maintain  the  circulation 
at  its  ordinary  rate  ;  and  we  are  not  justified,  therefore,  in  excluding 
those  sources  of  movement  in  the  higher  animals,  which  evidently 
exert  so  important  an  influence  in  the  lower. 

578.  The  force  with  which  the  heart  propels  the  blood  is  such,  that 
if  a  vertical  pipe  be  inserted  into  the  Carotid  artery  of  a  horse,  the  blood 
will  sometimes  rise  in  it  to  a  height  of  10  feet.  From  comparative 
experiments  upon  other  animals,  it  has  been  estimated  that  the- vigor- 
ous action  of  the  heart  in  Man  would  sustain  a  column  of  blood  in 
his  aorta  about  7^  feet  high ;  or,  in  other  words,  that  the  force  with 
which  the  heart  ordinarily  propels  the  blood  through  the  aorta,  is 
equal  to  that  which  would  be  generated  by  the  weight  of  a  column  of 
blood  of  the  same. size,  and  7 J  feet  high;  which  weight  would  be 
about  4J  lbs.  But  the  force  which  must  be  exerted  by  the  heart  to 
sustain  such  a  column,  may  be  shown,  upon  physical  principles,  to 
be  as  much  greater  than  this  as  the  area  of  a  plane  passing  through 


CIRCUMSTANCES  AFFECTING  RATE  OF  PULSE.  335 

the  base  and  apex  of  the  left  ventricle  is  greater  than  that  of  the  trans- 
verse section  of  the  aorta ;  and  as  the  proportion  of  these  arese  is  about 
3-1,  the  real  force  of  the  heart  may  be  stated  at  about  13  lbs. 

579.  The  number  of  contractions  of  the  heart,  in  a  given  time,  is 
liable  to  great  variations  within  the  limits  of  health,  from  several 
causes  ;  the  chief  of  which  are  diversities  of  Age  and  Sex,  amount  of 
Muscular  exertion,  the  condition  of  the  Mind,  the  state  of  the  Diges- 
tive system,  and  the  period  of  the  Day. — The  following  are  the  points 
of  greatest  importance,  in  regard  to  the  action  of  these  several  influ- 
ences : 

^ge. — The  pulse  of  the  newly-born  infant  averages  from  130  to  140 
per  minute ;  and  this  rate  gradually  diminishes,  until,  in  adult  age,  the 
pulse  averages  from  70  to  80 ;  and  in  the  decline  of  life  from  50  to  65. 

Sex, — The  pulse  of  the  adult  female  exceeds  that  of  the  adult  male 
in  frequency,  by  about  10  or  12  beats  in  a  minute ;  and  it  is  also 
more  liable  to  disturbance  from  other  causes. 

Muscular  exertion. — The  effect  of  this  in  accelerating  the  pulse  is 
well  known ;  but  as  the  amount  of  change  depends  upon  the  degree 
of  exertion,  no  general  statement  can  be  made  on  the  subject.  The 
continued  influence  of  a  moderate  degree  of  muscular  exertion,  is 
shown  by  the  effect  of  posture  upon  the  pulse.  Thus  the  pulse  is  on 
the  average  from  7  to  10  beats  faster  (per  minute)  in  the  standing 
than  in  the  sitting  posture  ;  and  4  or  5  beats  faster  in  the  sitting  than 
in  the  recumbent  posture.  This  amount  of  variation  is  temporarily 
increased  by  the  muscular  effort  required  for  the  change  of  posture ; 
but  this  soon  subsides  into  the  continued  rate,  which  the  permanent 
maintenance  of  the  new  posture  involves.  There  are  certain  states 
of  the  system,  in  which  the  heart's  action  is  increased  to  a  most  vio- 
lent degree,  by  a  simple  change  of  posture;  and  in  which,  therefore, 
it  is  necessary  that  even  this  slight  movement  should  be  made  with 
gentleness  and  caution. 

Mental  Condition.  The  action  of  the  heart  is  peculiarly  influenced, 
as  every  one  is  aware,  by  the  excitement  of  the  emotions.  This  is  a 
fact  to  which,  however  familiar,  the  medical  practitioner  should  con- 
stantly direct  his  attention.  The  trifling  agitation  occasioned  by  the 
entrance  of  the  medical  man  will  produce,  in  many  patients,  such  an 
acceleration  of  the  pulse,  as  would  be  very  alarming,  if  its  true  cause 
were  not  known.  And  the  real  rate  of  the  pulse  cannot  be  ascertained, 
until  time  has  been  permitted  for  the  agitation  to  subside ;  which  is 
favoured,  also,  by  the  influence  of  a  gentle  manner  and  tranquilizing 
conversation.  The  operation  of  the  intellectual  powers  does  not  seem 
to  affect  the  rate  of  the  heart's  movement  in  any  other  way,  than  by 
inducing  a  general  state  of  feverishness,  if  it  be  too  long  or  too  ener- 
getically kept  up. 

State  of  the  Digestive  System. — The  pulse  is  quickened  during  the 
digestion  of  a  meal ;  but  no  exact  numerical  statement  can  be  made 
on  this  subject. 

Period  of  the  Bay. — The  frequency  of  the  pulse  appears  to  be  some- 


336  INFLUENCE  OF  NERVES  UPON  HEART'S  ACTION. 

what  greater  in  the  morning  than  it  is  in  the  evening  ;  and  the  tem- 
porary action  of  any  of  the  preceding  causes  more  quickly  subsides 
in  the  evening  than  in  the  morning. 

580.  The  movements  of  the  heart  have  been  supposed  to  depend 
upon  a  constant  supply  of  nervous  influence,  generated  by  the  cerebro- 
spinal system,  and  transmitted  through  the  sympathetic  nerve,  the 
branches  of  which  are  copiously  distributed  to  it.  And  this  idea 
seemed  to  derive  support  from  the  fact,  that,  when  the  brain  and 
spinal  cord  are  removed,  or  when  large  portions  of  the^m  are  suddenly 
destroyed,  by  crushing  or  by  the  breaking  up  of  their  substance  in  any 
other  mode,  the  movements  of  the  heart  are  arrested.  But  it  has 
been  shown  that  the  brain  and  spinal  cord  may  h^  gradually  removed, 
without  any  such  consequence  ;  and  the  occasional  production  of  foe- 
tuses destitute  of  those  centres,  but  possessing  a  regularly-pulsating 
heart,  is  another  proof  that  the  movements  of  this  organ  do  not  depend 
upon  a  supply  of  nervous  influence  derived  from  them.  Still  they  are 
capable  of  being  influenced  by  impressions  transmitted  through  the 
nerves.  It  has  been  ascertained  by  Valentin,  that,  after  the  heart  has 
ceased  to  beat,  its  contractions  may  be  re-excited  by  stimulating  the 
roots  of  the  Spinal  Accessory  nerve,  or  of  the  first  four  Cervical 
nerves;  the  influence  of  that  stimulation  being  conveyed  to  the  heart 
by  the  Sympathetic  system,  the  cardiac  portion  of  which  communicates 
with  these  nerves.  Irritation  of  the  Par  Vagum,  also,  has  a  tendency 
to  accelerate  the  heart's  action,  or  to  re-excite  it  when  it  has  ceased  ; 
but  the  complete  severance  of  both  its  trunks  produces  little  disturb- 
ance in  the  regularity  of  the  movement.  The  action  of  the  heart  may 
be  also  affected  more  directly  through  the  sympathetic  system  ;  thus 
it  is  excited  by  irritation  of  the  cervical  ganglia,  especially  the  first ; 
whilst  continued  pressure  upon  the  cardiac  nerve,  by  an  enlarged 
bronchial  gland,  has  appeared  to  be  the  cause  of  its  occasional  sus- 
pension. It  is  without  doubt  through  its  nervous  connections,  and 
probably  though  the  sympathetic  system,  that  the  heart  receives  the 
influence  of  mental  emotions. 

581.  The  movements  of  the  heart  maybe  suspended,  or  altogether 
checked,  by  sudden  and  violent  impressions  on  the  nervous  centres, 
even  though  these  do  not  occasion  any  perceptible  breach  of  substance. 
Thus  in  concussion  of  the  brain,  there  is  not  merely  insensibility,  but 
also  a  complete  suspension  of  the  circulation,  occasioned  by  a  failure 
of  the  heart's  power.  This  suspension  may  be  permanent,  so  that 
animation  cannot  be  restored  ;  or  it  may  be  temporary,  as  in  ordinary 
fainting.  The  well-known  influence  of  blows  upon  the  epigastrium, 
in  producing  sudden  death,  is  probably  to  be  attributed  to  a  similar 
cause, — namely,  the  shock  thus  communicated  to  the  extensive  plexus 
of  ganglionic  nerves,  radiating  from  the  semilunar  ganglia,  and  pro- 
ceeding to  the  abdominal  viscera.  Violent  impressions  upon  other 
nervous  expansions  may  produce  a  dangerous  weakening  of  the 
heart's  contractile  power ;  this  is  the  case,  for  example,  with  exten- 
sive burns,  which  may  produce  faintness,  and  even  death,  especially 


EQUALIZATION  OF  FLOW  IN  THE  ARTERIES.  337 

in  children,  by  the  depression  which  they  induce.  Many  other  causes 
of  sudden  suspension  of  the  heart's  action  might  be  enumerated  ;  but 
they  may  be  generally  traced  to  a  strong  impression  upon  the  nervous 
system  ;  though  of  the  mode  in  which  this  operates  we  know  nothing. 

4.  Movement  of  the  Blood  in  the  Arteries. 

582.  The  Blood,  thus  propelled  from  the  Heart  into  the  Arteries 
by  a  series  of  interrupted  jets,  would  continue  to  flow  in  the  same 
manner,  if  it  were  not  for  the  equalization  of  its  movement,  effected 
by  the  properties  of  the  arterial  walls.  This  influence  is  exerted  by 
the  middle  or  fibrous  coat,  which  consists  in  part  of  yellow  elastic 
tissue  (§  189),  and  in  part  of  non-striated  muscular  fibre  (§  337). 
The  proportion  of  these  two  components  varies  in  arteries  of  different 
calibre ;  the  muscular  tissue  being  thicker  in  the  smaller  branches, 
and  the  elastic  tissue  being  found  in  larger  amount  in  the  main 
trunks. 

583.  It  is  chiefly  to  the  simple  physical  property  of  Elasticity,  thus 
possessed  by  the  Arterial  tubes,  that  we  owe  the  equalization  of  the 
flow  of  blood;  and  we  may  hence  understand  the  reason,  why  the 
trunks  that  are  in  nearest  connection  with  the  heart,  should  be  those 
most  endowed  with  it.  If  a  forcing- pump  were  to  inject  water,  by 
successive  strokes,  into  a  system  of  tubes  with  perfectly  unyielding 
walls,  the  flow  of  fluid  at  the  farther  extremities  of  these  tubes  would 
be  as  much  interrupted,  as  its  entrance  into  them.  But  if  the  pump 
be  connected  with  an  air-vessel  (as  in  the  common  fire-engine),  so 
that  a  part  of  the  force  of  each  stroke  is  expended  in  compressing  the 
air,  the  expansion  of  this,  during  the  interval  between  the  successive 
strokes,  produces  a  continuous  flow  of  water  along  the  tubes.  Or  if 
the  tubes  themselves  were  endowed  wuth  a  certain  degree  of  elasticity, 
which  should  allow  them  to  dilate  near  their  commencement,  so  as  to 
receive  the  new  charge  of  fluid,  and  which  should  occasion  a  con- 
tinued pressure  upon  the  fluid  during  the  intervals  of  the  stroke,  the 
same  equalizing  effect  would  be  produced.  This  is  precisely  the 
case  with  the  Arterial  system;  the  intermittent  jets,  by  which  the 
blood  is  propelled  from  the  heart,  are  speedily  converted  into  a  con- 
tinued stream  ;  so  that,  at  even  a  moderate  distance  from  the  heart, 
the  only  indication  of  its  interrupted  action  is  presented  by  the  greater 
or  less  rapidity  of  the  flow;  and  this  gives  rise,  when  an  artery  is 
divided,  to  an  alternate  rise  and  fall  of  the  jet  of  blood,  and,  in  the 
ordinary  circulation,  to  the  phenomenon  called  the  pulse.  This  is  due 
to  an  increase  in  the  dimensions  of  the  arterial  tube,  both  in  length 
and  breadth,  with  each  additional  ingress  of  blood  ;  the  increase  in 
length  is  the  more  considerable  of  the  two  effects,  and  causes  the 
artery  to  be  somewhat  lifted  from  its  seat.  During  the  intervals,  a 
quantity  of  blood  corresponding  to  that  which  had  entered,  escapes 
by  the  further  extremity  of  the  tube;  and  thus  the  artery  is  enabled 
to  contract  to  its  previous  dimensions,  and  to  return  to  its  bed.     We 

22 


338       •  EFFECTS  OF  MUSCULARITY  OF  ARTERIES. 

may  compare  the  pulse,  therefore,  to  a  wave,  which  commences  in 
the  heart,  and  travels  onwards  through  the  arterial  system. 

584.  In  the  large  arteries  near  the  heart,  the  pulsation  is  always 
precisely  synchronous  with  the  ventricular  systole ;  but  it  takes  place 
somewhat  later  in  the  arteries  at  a  distance  from  the  heart;  the  time 
•required  for  the  transmission  of  the  wave  being  proportioned  to  the 
degree  in  which  the  walls  of  the  arteries  yield  to  it.  If  they  were 
quite  rigid,  the  egress  at  one  extremity  must  take  place  at  the  precise 
moment  that  the  fluid  is  forced  into  the  other.  On  the  other  hand,  if 
the  walls  be  too  easily  distensible,  they  yield  to  the  propelling  force 
in  such  a  degree  that  it  is  entirely  expended  upon  them ;  and  the  fluid 
is  not  moved  onwards  at  all,  or  but  very  slowly.  In  the  healthy  state 
of  the  arterial  walls,  they  should  contract  upon  their  contents,  with 
sufficient  force  to  equalize  the  flow  of  blood,  and  to  prevent  the  pulse- 
wave  from  occupying  more  than  one-sixth  or  one-seventh  of  a  second, 
in  its  propagation  to  the  remotest  arteries  of  the  system ;  and  the  pulse 
should  be  full,  producing  a  prolonged  but  gentle  elevation  beneath 
the  finger,  and  capable  of  resisting  moderate  pressure.  This  condition 
is  dependent  in  great  part  upon  the  due  tonicity  of  the  muscular  coat 
of  the  arteries  (§  365).  When  this  tonicity  is  in  excess,  the  walls  of 
the  arteries  are  too  rigid  ;  the  pulse  at  the  wrist  is  felt  to  occur  exactly 
at  the  same  time  with  the  ventricular  systole;  and  its  character  is  that 
of  strength,  incompressibility,  and  sustained  power,  though  it  may  be 
even  slower  than  usual.  This  is  the  case  in  what  is  commonly  termed 
*'high  condition"  of  the  system;  which  predisposes  to  inflammatory 
disorders,  but  which  renders  it  less  susceptible  than  usual  to  the  influ- 
ence of  malaria,  contagious  miasmata,  or  other  causes  of  a  depressing 
character.  On  the  other  hand,  when  the  tonicity  of  the  arteries  is 
less  than  it  should  be,  their  walls  yield  too  much  to  the  pulse-wave ; 
so  that  the  pulse  at  the  wrist  is  often  felt  even  after  the  second  sound 
is  heard ;  and  the  pulse  itself  is  jerking,  unsteady,  and  too  easily 
compressible.  This  loose  relaxed  state  of  the  vessels  is  the  most 
unfavourable  that  can  be  to  regularity  and  vigour  of  the  circulation  ; 
and  it  manifests  its  ill  effects  in  the  general  condition  of  the  system, 
which  is  then  peculiarly  prone  to  suffer  from  the  agency  of  malaria, 
infectious  miasmata,  or  any  other  depressing  causes. 

585.  Although  many  Physiologists  have  denied  that  the  Arteries 
possess  real  Muscular  Contractility  in  any  degree,  yet  there  can  be  no 
longer  any  doubt  on  the  subject;  since  numerous  experimenters  have 
succeeded  in  producing  distinct  contraction  in  their  walls,  by  the 
application  of  those  stimuli  which  act  upon  muscular  fibre  in  general. 
Moreover  it  has  been  ascertained,  that  when  an  artery  is  dilated  by 
the  blood  injected  into  it  from  the  heart,  it  reacts  with  a  force  superior 
to  the  impulse  to  which  it  yielded ;  and  that,  if  a  portion  of  an  artery 
from  an  animal  recently  dead,  in  which  the  vital  properties  are  still 
preserved,  and  a  similar  portion  from  an  animal  that  has  been  dead 
some  days,  in  which  nothing  but  the  elasticity  remains,  be  distended 
with  equal  force,  the  former  contracts  to  a  much  greater  degree  than 


EFFECTS  OF  MUSCULARITY  OF  ARTERIES.  339 

the  latter,  after  the  distending  force  is  withdrawn. — One  use  of  this 
contractile  power  may  very  probably  be,  to  assist  the  Heart  in  main- 
taining the  flow  of  blood  ;  for  if  the  Arterial  walls  yield  readily  to  the 
ingress  of  blood,  and  then  contract  upon  their  contents  with  a  force 
greater  than  that  which  distended  them,  the  current  must  necessarily 
be  propelled  onwards  with  greater  force.  This  supplementary  pro- 
pelling force,  on  the  part  of  the  arteries,  may  serve  as  a  compensation 
to  that  diminution  of  the  heart's  power,  which  must  result  from  the 
increased  friction  of  the  blood  against  the  walls  of  the  vessels  occa- 
sioned by  their  subdivision  ;  and  we  thus  observe,  even  in  the  highest 
animals,  some  traces  of  that  diffused  agency,  on  which  the  Circulation 
is  so  much  more  dependent  in  the  lower  tribes. 

586.  It  seems  probable,  however,  that  one  chief  use  of  the  Mus- 
cularity of  the  Arterial  walls  consists  in  its  regulation  of  the  diameter 
of  the  tubes,  in  accordance  with  the  quantity  of  blood  to  be  con- 
ducted through  them  to  any  part ;  the  proper  amount  being  deter- 
mined by  circumstances  at  the  time.  Such  local  changes  may  form 
a  part  of  ihe  regular  series  of  actions  of  the  human  body,  as  when 
the  Uterine  and  Mammary  arteries  undergo  enlargement,  at  the 
periods  of  pregnancy  and  parturition ;  and  they  occur  still  more  fre- 
quently in  diseases,  which  are  attended  by  increased  action  of  par- 
ticular organs.  In  such  cases,  it  cannot  be  vis  a  tergo  of  the  Heart, 
that  occasions  the  enlargement  of  certain  arterial  trunks,  and  of  no 
others;  since  any  increase  in  its  propulsive  power  would  affect  all 
alike.  It  must  be,  therefore,  through  a  power  inherent  in  themselves, 
that  the  dilatation  takes  place ;  and  there  seems  much  reason  for 
attributing  to  the  Sympathetic  system  of  nerves  a  control  over  this 
power,  and  consequently  the  office  of  regulating  the  local  distribution 
of  blood,  in  accordance  with  the  wants  of  the  different  parts.  It  is 
well  known  that  the  nerves  of  this  system  are  copiously  distributed 
upon  the  arterial  walls  ;  and  it  has  been  experimentally  shown,  that 
they  have  the  power  of  producing  contractions  in  the  larger  arteries. 
Moreover,  there  is  every  reason  to  believe,  that  the  diameter  of  the 
Capillary  blood-vessels,  and  the  rate  of  the  movement  of  blood 
through  them,  are  much  influenced  by  these  nerves  (§  603);  and  it 
seems  highly  probable,  therefore,  that  they  should  have  a  correspond- 
ing influence  upon  the  size  of  the  trunks,  from  w^hich  these  capilla- 
ries are  derived. 

587.  The  Arterial  system  possesses  nearly  the  same  relative  capa- 
city in  every  part:  that  is,  if  a  section  could  be  made  through  all 
the  systemic  arteries  at  a  certain  distance  from  the  heart,  the  united 
areas  would  be  found  equal  to  that  of  the  aorta ;  and  those  of  the 
branches  of  the  pulmonary  arteries  would  equal  those  of  their  trunk. 
This  results  from  the  fact,  that,  at  every  subdivision,  the  united  areas 
of  the  branches  are  almost  precisely  equal  to  that  of  the  trunk  from 
which  they  proceeded ;  although  the  united  diameters  of  the  former 
far  exceed  that  of  the  latter.  According  to  a  well-known  mathemati- 
cal law,  the  areas  of  circles  are  as  the  squares  of  the  diameters;  con- 


340  RAMIFICATION  AND  ANASTOMOSIS  OF  ARTERIES. 

sequently,  in  making  such  comparisons,  it  is  necessary  to  square  the 
diameters  of  the  trunk  and  those  of  the  branches,  and  to  contrast  the 
former  with  the  sum  of  the  latter.  Thus  a  trunk  whose  diameter  is 
7,  may  subdivide  into  two  branches,  each  having  a  diameter  of  nearly 
5;  for  the  square  of  7  is  49,  and  twice  the  square  of  5  is  50.  Or  a 
trunk  whose  diameter  is  17  may  subdivide  into  three  branches,  whose 
diameters  are  10,  10,  and  9J  (making  29J  as  the  sum  of  the  diame- 
ters) ;  for  the  square  of  the  diameter  of  the  trunk  is  289,  whilst  the 
sum  of  the  squares  of  those  of  the  branches, is  290:^.  It  appears 
from  Mr.  Paget's  recent  admeasurements,  that  there  is  seldom  an 
exact  equality  between  the  area  of  the  trunk  and  that  of  its  branches ; 
the  area  sometimes  increasing,  and  sometimes  diminishing.  The 
former  seems  the  general  rule  in  the  upper  extremities;  the  latter  in 
the  lower.  Thus  the  area  of  the  trunk  of  the  external  carotid  is  to  that 
of  its  branches,  as  100  to  119  ;  whilst  the  area  of  the  abdominal  aorta, 
just  before  its  final  division,  is  to  that  of  its  branches  as  100  to  89. 

588.  In  almost  every  part  of  their  course,  the  ramifications  of  the 
arteries  communicate  freely  with  each  other,  by  anastomosis ;  and  this 
communication  is  most  important,  as  affording  the  means  by  which 
the  circulation  is  sustained,  when  the  current  through  the  main  trunk 
is  obstructed.  There  is  scarcely  an  artery  in  the  body,  except  the 
aorta,  which  may  not  be  tied,  with  the  certainty  that  the  blood  will 
still  be  conducted  to  its  destination,  by  the  collateral  circulation.  At 
first,  the  quantity  which  thus  passes  is  very  insignificant,  and  is  by 
no  means  sufldcient  to  supply  what  is  needed  ;  thus,  when  the  femoral 
artery  has  been  tied  for  popliteal  aneurism,  the  limb  becomes  cold, 
and  the  sensibility  of  its  surface  and  its  muscular  powder  are  alike 
diminished.  In  a  few  hours,  however,  its  warmth  returns,  and  its 
sensibility  and  muscular  power  are  restored ;  indicating  that  its 
circulation  has  been  already  re-established  through  the  collateral 
branches.  And  where  an  opportunity  presents  itself  at  a  subsequent 
period  for  examining  the  state  of  the  vessels  in  such  a  limb,  it  is 
found  that  an  extraordinary  enlargement  has  taken  place  in  arteries 
that  were  previously  of  insignificant  size,  which  form  a  communica- 
tion between  the  branches  that  issued  above  and  below  the  inter- 
ruption. Moreover,  it  is  commonly  found,  that  the  main  trunk  has 
become  completely  impervious  above  the  part  where  it  was  oblite- 
rated by  the  ligature,  up  to  the  point  at  which  the  nearest  lateral 
branch  is  given  off. — Even  the  abdominal  aorta  has  been  tied  in 
dogs,  without  fatal  results;  the  circulation  in  the  posterior  part  of 
the  body,  and  in  the  hinder  extremities,  being  then  maintained 
chiefly  by  the  inosculation  of  the  external  mammary  artery  with  the 
epigastric,  upon  the  parietes  of  the  abdomen. 

T>.  Movement  of  Blood  in  the  Capillaries. 

589.  The  ultimate  ramifications  of  the  Arteries  pass  so  insensibly 
ifito  those  of  the  Veins,  that  no  definite  line  of  demarkation  between 


ARRANGEMENT  OF  CAPILLARY  VESSELS,  341 

them  can  be  drawn ;  and  although  we  are  in  the  habit  of  speaking  of 
the  "Capillaries"  as  a  distinct  system  of  vessels,  yet  it  ought  to  be 
strictly  borne  in  mind,  that  they  differ  only  in  size  from  the  vessels, 
from  which  they  receive  their  blood  on  the  one  side,  and  into  which 
they  pour  it  on  the  other.  It  was  at  one  time  supposed  that  they  are 
merely  channels  or  passages,  excavated  in  the  tissues,  having  no 
definite  walls  of  their  own.  This  is  probably  true  of  them  in  the 
lower  tribes  of  Animals ;  and  it  may  also  be  the  case  at  an  early 
stage  of  their  development  in  the  higher.  But  when  their  formation 
is  complete,  they  undoubtedly  possess  w^alls  of  a  fibrous  texture,  as 
distinct  as  those  of  the  arteries  and  veins,  though  of  extreme  thin- 
ness. From  the  occasional  appearance  of  bodies  resembling  cell- 
nuclei,  in  the  substance  of  the  walls  of  the  capillaries,  it  has  been 
thought  that  their  tubes  are  formed,  in  the  first  instance,  by  the 
coalescence  of  cells  arranged  in  a  linear  direction;  and  this  idea 
receives  confirmation  from  the  fact,  that  the  ducts  of  Plants  are 
undoubtedly  formed  in  this  manner,  and  not  by  the  mere  retirement 
of  the  tissues  on  either  side  leaving  an  intervening  channel.  The 
closely-reticulated  structure  usually  formed  by  the  capillaries,  has 
commonly  been  regarded  as  distinguishing  them  both  from  the  arte- 
ries and  the  veins;  and  it  is  not  uncommon  to  speak  of  the  arteries 
as  delivering  the  blood  into  the  "capillary  network,"  and  the  veins 
as  receiving  the  fluid  that  has  traverseid  this.  Such  expressions  are 
not  incorrect  as  implying  the  simple  fact,  that  between  the  arteries 
and  the  veins  is  a  network  of  minute  vessels,  through  which  the  blood 
has  to  travel  when  proceeding  from  one  to  the  other  ;  but  these  vessels 
must  not  be  regarded  as  belonging  to  a  distinct  class,  being  nothing 
else  than  the  minutest  subdivisions  of  the  veins  and  arteries,  which 
commonly  inosculate  freely  with  each  other. 

590.  The  degree  of  this  inosculation,  and  the  consequent  form  of 
the  capillary  network,  are  subject,  however,  to  very  great  variations; 
and  these  may  be  generally  shown  to 
have  a  relation  to  the  form  of  the  ulti-  ^'s  ^^■ 

mate  elements  of  the  tissues,  which  are 
traversed  by  the  capillaries.  Thus  we 
see  in  the  capillaries  of  Muscle,  that  the 
major  part  run  parallel  to  the  course  of 
the  fibres,  lying  in  the  minute  interspaces 
between  them  (Fig.  88) ;  a  few^  trans- 
verse branches  serving  to  connect  them 

with  each  other.       A  similar  distribution  Capillary  network  of  Muscle. 

prevails  in  the  capillaries  of  the  Nervous 
trunks ;  but  those  of  the  Nervous  centres  are  arranged  in  the  form  of 
a  minute  network,  so  as  completely  to  traverse  every  part  of  the  struc- 
ture (Fig.  89).  Again,  we  observe  that  the  capillaries  of  Glands  form 
a  minute  network  around  the  secreting  follicles  (Fig.  90) ;  and  a  simi- 
lar arrangement  prevails  in  the  capillaries  of  the  air-cells  of  the  lungs, 
which  are  set  so  closely  together,  that  it  would  seem  as  if  the  purpose 


342 


DISTRIBUTION  OF  THE  CAPILLARIES. 


were  to  cover  the  surface  with  blood  as  completely  as  possible,  con- 
sistently with  its  being  retained  within  vessels,  and  not  spread  out 


Fig.  69. 


Fig.  90. 


Capillary  Network  of  Nervous  Centres. 


Capillary  Network  around  the  follicles  of 
Parotid  Gland. 


into  a  continuous  film  (Fig.  102).  A  network  of  very  much  the  same 
character  is  found  in  the  villi  of  the  mucous  membrane  (Fig.  77),  on 
the  ordinary  surface  of  simple  mucous  membrane  (Fig.  91),  and  on 


Fig.  91. 


Fig.  92. 


Capillary  Network  in  simple  mu- 
cous membrane  of  palpebral  con- 
junctiva. 


Capillary  Network  in  choroid  coat 
of  the  eye. 


that  of  the  choroid  coat  of  the  eye  (Fig.  92).  Where  the  surface  of 
the  mucous  membrane  is  depressed  into  follicles,  the  arrangement  of 
the  capillaries  has  an  evident  reference  to  these  (Fig.  93) ;  whilst,  on 


Fig.  93. 


Fig.  94. 


Distribution  of  Capillaries  around 
follicles  of  Mucous  Membrane. 


Distribution  of  Capillaries  at  the  sur- 
face of  the  skin  of  the  finger. 


VARYING  SIZE  OF  THE  CAPILLARIES.  343 

the  other  hand,  where  the  surface  of  the  skin  is  raised  up  into  sensory 
papillse,  the  capillary  network  sends  looped  prolongations  into  these, 
which  are  found  accompanying  their  nerves  (Figs.  94  and  95.) 

591.  It  cannot  be  supposed  that  the  ar- 
rangement of  the  vessels  has  any  further  ^'^•^^• 
influence  upon  the  function  of  the  part  they 
supply,  than  that  w^hich  it  derives  from  the 
regulation  of  the  supply  of  blood  afforded 
to  each  individual  portion  of  the  structure. 
The  form  of  the  capillary  network  is  evi- 
dently determined  by  that  of  the  elements 
of  the  tissues  permeated  by  it ;  these  are 
the   real  operative   instruments   in  every 

part;  and  the  distribution  of  the  blood-  papXoTthe tongue.  °  ""S'*'™ 
vessels  is  so  arranged,  as  to  afford  them 

precisely  the  amount  of  nourishment  they  respectively  require.  Thus 
we  have  seen,  that  there  are  many  living  parts,  possessing  most  im- 
portant functions,  in  the  human  body,  which  are  not  in  any  direct 
relation  with  blood-vessels,  and  which  yet  derive  their  whole  nutri- 
ment, and  the  materials  of  their  functional  operations,  from  the  blood. 
This  is  the  case,  for  example,  with  the  whole  of  epithelial  and  epi- 
dermic cells  ;  and  also  with  the  articular  cartilages,  and  the  substance 
of  the  teeth.  Even  in  bone,  the  islets  between  the  Haversian  canals, 
which  are  completely  unpenetrated  by  vessels,  are  of  considerable 
size.  Such  islets  must  everywhere  exist,  between  the  meshes  of  the 
capillary  network;  so  that  the  question  of  the  vascularity  or  non-vas- 
cularity  of  a  tissue  is  one  of  degree  only; — the  ultimate  fibre  of 
muscle  or  nerve,  and  the  cells  and  fibres  of  other  tissues,  being  as 
completely  non-vascular,  as  the  entire  substance  of  a  tooth  or  of  an 
articular  cartilage;  the  latter  being  nourished,  like  the  former,  by 
imbibition  from  the  surrounding  vessels. 

592.  The  term  "  Capillary"  may  be  employed  in  an  extended  or  a 
restricted  sense  ;  in  the  former  it  includes  all  the  minute  vessels, 
which  pass  between  the  arteries  and  the  veins ;  in  the  latter  it  is  ap- 
plied only  to  those,  which  admit  no  more  than  a  single  file  of  blood- 
discs  at  once,  and  excludes  those,  which  admit  two,  three,  or  even 
four  rows,  even  although  they  establish  a  direct  communication  from 
one  side  of  the  network  to  the  other.  The  former  application  of  the 
term  is  the  most  convenient,  although  perhaps  not  the  most  strictly 
accurate  ;  and  it  will  be  therefore  here  employed  in  its  extended 
sense.  And  this  is  rendered  more  correct  by  the  fact,  that  the  size  of 
the  individual  capillaries  is  by  no  means  permanent ;  an  enlargeme;it 
often  taking  place  in  ope,  and  a  contraction  in  others,  at  the  same 
time:  so  that  vessels,  which  were  previously  true  capillaries,  no 
longer  remain  such  ;  and  passages,  which  were  previously  of  far 
greater  calibre,  are  reduced  to  the  average  diameter. 

593.  The  opinion  was  long  entertained,  that  there  are  vessels 
adapted  to  the  supply  of  the  white  or  colourless  tissues ;  carrying 


344  VARYING  SIZE  OF  THE  CAPILLARIES. 

from  the  arteries  only  the  fluid  portion  of  the  blood,  or  liquor  sangui- 
nis^ and  leaving  the  rest  behind.  No  other  such  vessels  have  been 
really  observed,  however,  than  capillaries  in  a  state  of  unusual  con- 
traction, as  just  now  mentioned.  And  it  may  be  safely  affirmed,  that 
the  supposition  of  their  existence  is  not  required.  For  any  one  who 
observes  the  smallest  capillary  vessels  under  the  microscope,  may 
perceiv^e,  that  the  current  of  blood  which  passes  through  them  is 
almost  free  from  (folour, — as  the  red  corpuscles  themselves  appear  to 
be,  when  spread  out  in  a  single  layer.  Tissues  which  are  rather 
scantily  permeated  by  such  vessels,  therefore,  may  still  be  white  ;  and 
it  is  only  where  the  network  is  very  close,  and  the  quantity  of  blood 
which  passes  through  it  is  consequently  great,  that  a  perceptible 
colour  will  be  communicated  by  the  red  corpuscles.  And  we  have 
seen,  that  the  idea  that  Nutrition  can  only  be  carried  on  by  direct 
communication  with  vessels,  is  entirely  unfounded ;  the  tisjsues  into 
which  no  blood-vessels  can  be  traced,  being  adapted  to  nourish  them- 
selves, like  cellular  Plants,  by  the  imbibition  of  fluid  at  their  surfaces, 
on  which  vessels  are  (for  the  most  part)  copiously  distributed. 

594.  That  the  blood  can  only  minister  to  the  operations  of  Nutri- 
tion, Secretion,  &c.,  whilst  it  is  circulating  through  the  Capillaries, 
is  evident  from  several  considerations.  The  thickness  of  the  walls  of 
the  larger  vessels  interposes  an  effectual  barrier  to  its  transudation  ; 
and  so  completely  is  the  blood  cut  off,  even  from  penetrating  these, 
that  they  do  not  derive  their  own  nourishment  from  the  blood  which 
flows  in  their  own  tubes,  but  from  a  capillary  network  in  their  own 
substance,  which  is  supplied  by  vessels  from  collateral  branches, — 
these  being  termed  the  vasa  vasorum.  Moreover  it  is  by  the  inoscu- 
lation of  the  capillaries  alone,  that  the  minute  network  is  formed, 
which  serves  to  bring  the  blood  into  proximity  with  the  minute  parts 
of  the  tissues  to  be  nourished  ;  thus  let  it  be  supposed  that  the  minute 
arteries  of  Muscle  were  to  terminate  in  veins,  without  undergoing 
further  subdivision,  the  islets  left  between  their  anastomosing  branches 
would  be  far  too  large,  and  the  nutritive  materials  would  consequently 
not  be  supplied  with  sufficient  readiness,  even  supposing  that  it  could 
freely  permeate  the  walls  of  these  vessels. — The  Capillaries,  then, 
must  not  be  regarded  as  altogether  distinct  in  their  endowments,  from 
the  vessels  with  which  they  are  connected  on  either  side  ;  but  merely 
as  intended,  by  their  minute  subdivision  and  inosculation,  to  bring 
the  blood  into  sufficiently  close  relation  with  the  tissues  they  are  to 
nourish,  and  to  allow  a  greater  degree  of  transudation  of  its  elements 
by  the  comparative  thinness  of  their  walls. 

595.  When  the  flow  of  blood  through  the  capillaries  of  a  transpa- 
rent part,  such  as  the  web  of  a  Frog's  foot,  is  observed  with  the 
microscope,  it  appears  at  first  to  take  place  with  great  evenness  and 
regularity.  The  influence  of  the  contractions  of  the  heart  may  be 
seen  to  extend  itself  into  the  smaller  arteries ;  the  blood  moving  on- 
wards in  them  with  a  somew^hat  jerking  motion.  But  this  influence 
altogether  disappears  in  the  Capillary  network ;  the  flow  of  blood 


VARIATIONS  IN  FLOW  OF  BLOOD  IN  CAPILLARIES.  345 

through  this  being  even  and  continuous,  except  Avhen  the  action  of 
the  heart  is  becoming  weak  and  irregular,  or  when  its  influence  is 
impeded  by  obstruction  in  the  vessels  leading  to  the  part, — the  blood 
being  then  impelled  by  a  succession  of  jerks,  with  intervals  of  com- 
plete repose. — But  on  watching  the  movement  for  some  time,  various 
changes  may  be  observed,  which  cannot  be  attributed  to  the  heart's 
influence,  and  which  show  that  a  certain  regulating  or  distributive 
power  exists  in  the  walls  of  the  capillaries,  or  in  the  tissues  which 
they  traverse.  Not  only  do  we  occasionally  perceive  some  of  the 
tubes  enlarging,  so  as  to  admit  several  files  of  blood-discs  instead  of 
one,  whilst  others  that  previously  received  several,  now  only  admit  one ; 
— but  we  also  see  vessels  coming  into  view,  which  were  not  previously 
noticed,  whilst  other  vessels  seem  to  become  obliterated.  This  appa- 
rently new  formation  and  obliteration  of  vessels,  however,  do  not 
really  take  place ;  for  a  more  close  examination  shows,  that  the  former 
of  these  appearances  is  due  to  the  entrance  of  red  corpuscles  into 
passages,  which  existed  before,  but  which  w^ere  in  such  a  state  of 
contraction  as  enabled  them  only  to  admit  the  fluid  portion  of  the 
blood ;  whilst,  by  a  converse  change  in  certain  capillaries,  from  the 
dilated  to  the  contracted  state,  the  appearance  of  obliteration  is  pro- 
duced, the  red  corpuscles  being  excluded,  and  the  transparent  fluid 
of  the  blood  being  alone  transmitted  by  them. 

596.  But  these  are  by  no  means  all  the  irregularities,  which  may 
be  detected  by  a  close  scrutiny  of  the  Capillary  circulation.  The 
velocity  of  the  current  is  liable  to  great  and  sudden  variations,  which 
cannot  be  accounted  for  by  any  change  in  the  heart's  action,  or  in  the 
supply  of  blood  aflforded  by  the  arteries ;  and  this  change  may  mani- 
fest itself,  either  in  the  w^hole  capillary  network  of  a  part,  or  in  a  por- 
tion of  it, — the  circulation  taking  place  with  diminished  rapidity  in 
one  part,  and  with  increased  energy  in  another,  though  both  are  sup- 
plied by  the  same  trunk.  These  variations  are  sometimes  manifested 
by  the  complete  change  in  the  direction  of  the  movement,  in  certain 
of  the  transverse  or  communicating  branches;  this  movement  taking 
place,  of  course,  from  the  stronger  towards  the  w^eaker  current.  Not 
unfrequently  an  entire  stagnation,  of  longer  or  shorter  duration,  pre- 
cedes the  reversal  of  the  direction.  Irregularities  of  this  kind  are 
most  frequent,  when  the  heart's  action  is  enfeebled  or  partially  inter- 
rupted ;  and  it  would  thus  appear,  that  the  local  influences  by  which 
they  are  produced,  are  overcome  by  the  propelling  power  of  the  cen- 
tral organ,  when  this  is  acting  with  its  full  vigour.  When  the  whole 
current  has  nearly  stagnated,  and  a  fresh  impulse  from  the  heart  re- 
news it,  the  movement  is  seldom  uniform  through  the  entire  plexus 
supplied  by  one  trunk  ;  but  is  much  greater  in  some  of  the  tubes  than 
in  others, — the  variation  being  in  no  degree  connected  with  their  size, 
and  being  very  different  in  its  amount  at  short  intervals. 

597.  AH  these  circumstances  indicate  that  the  movement  of  blood 
through  the  Capillaries  is  very  much  influenced  by  local  forces  ; 
although  these  forces  are  not  sufficiently  powerful,  in  the  higher  ani- 


346 


MOVEMENT  OF  BLOOD  IN  CAPILLARIES. 


mals,  to  maintain  it  alone.  And  from  other  facts  it  appears,  that  the 
conditions  necessary  for  the  energetic  flow  of  blood  through  these 
vessels,  are  nothing  else  than  the  active  performance  of  the  nutritive 
and  other  operations,  to  which  they  are  subservient.  The  examina- 
tion of  a  single  one  of  these  processes,  will  afford  us  the  requisite 
proof.  The  blood  when  circulating  through  the  systemic  capillaries, 
yields  a  portion  of  its  oxygen  to  the  tissues  it  permeates,  and  receives 
from  them  carbonic  acid.  On  the  other  hand,  when  passing  through 
the  pulmonary  capillaries,  it  gives  up  its  carbonic  acid  to  the  atmo- 
sphere, and  imbibes  a  fresh  supply  of  oxygen.  Now  if  either  of 
these  changes  be  prevented  from  taking  place,  a  retardation  and  even 
a  complete  stagnation,  of  the  blood  will  take  place, — the  flow  through 
the  capillaries  being  now  resisted,  instead  of  accelerated,  by  the  rela- 
tion which  the  blood  bears  to  the  tissues.  Thus  it  has  been  shown, 
that  if  an  animal  be  partially  deprived  of  oxygen,  so  that  the  arterial 
blood  is  not  duly  aerated  (rather  resembling  the  ordinary  venous 
blood),  and  cannot  exert  its  proper  action  on  the  tissues,  the  pressure 
upon  the  walls  of  the  systemic  arteries  is  increased,  although  the  supply 
of  blood  propelled  by  the  heart,  and  the  propulsive  power  of  the 
heart  itself,  are  diminished  ;  and  this  plainly  indicates  a  retardation  in 
the  systemic  capillaries,  producing  an  undue  accumulation  in  the 
arteries. — On  the  other  hand,  the  suspension  of  the  supply  of  oxygen 
to  the  lungs,  either  by  an  obstruction  in  the  air-passages,  or  by  caus- 
ing the  animal  to  breathe  some  other  gas,  brings  the  pulmonary  cir- 
culation to  a  stand  in  a  very  short  time,  the  blood  not  being  able  to 
undergo  its  usual  changes  in  the  capillaries  of  those  organs ;  and  by 
this  stagnation,  the  whole  movement  of  blood  is  speedily  checked. 
The  readmission  of  oxygen,  if  the  suspension  of  the  circulation  have 
not  been  too  long  continued,  occasions  the  renewal  of  the  movement 
in  the  capillaries,  and  thence  in  the  whole  circle  of  vessels ;  and  this 
even  after  the  heart  has  ceased  to  propel  blood  towards  the  lungs. 

598.  The  principles  already  noticed  (§  547),  as  put  forth  by  Prof. 
Draper,  seem  fully  adequate  to  explain  these  phenomena.  The  arte- 
rial blood, — containing  oxygen  with  which  it  is  ready  to  part,  and 
being  prepared  to  receive  in  exchange  the  carbonic  acid  which  the 
tissues  set  free, — must  obviously  have  a  greater  affinity  for  the  tissues, 
than  venous  blood,  in  which  both  these  changes  have  already  been 
effected.  Consequently,  upon  mere  physical  principles,  the  arterial 
blood,  which  enters  the  systemic  capillaries  on  one  side,  must  drive 
before  it,  and  expel  on  the  other  side  of  the  network,  the  blood  which 
has  become  venous  whilst  traversing  it.  But  if  the  blood  which 
enters  the  capillaries  have  no  such  affinity,  no  such  motor  power  can 
be  developed.  On  the  other  hand,  in  the  capillaries  of  the  lungs, 
the  opposite  affinities  prevail.  The  venous  blood  and  the  air  in  the 
pulmonary  cells  have  a  mutual  attraction,  which  is  satisfied  by  the 
exchange  of  oxygen  and  carbonic  acid  that  takes  place  through  the 
walls  of  the  capillaries  ;  and  when  the  blood  has  become  arterialized, 
it  no  longer  has  any  attraction  for  the  air.     Upon  the  very  same  prin- 


VARIOUS  CONDITIONS  OF  CAPILLARY  CIRCULATION.  347 

ciple,  therefore,  the  venous  blood  will  drive  the  arterial  before  it,  in 
the  pulmonary  capillaries,  whilst  respiration  is  properly  going  on  :  but 
if  the  supply  of  oxygen  be  interrupted,  so  that  the  blood  is  no  longer 
aerated,  no  change  in  the  affinities  takes  place  whilst  it  traverses  the 
capillary  network  ;  the  blood,  continuing  venous,  still  retains  its  need 
of  a  change  and  its  attraction  for  the  walls  of  the  capillaries  ;  and  its 
egress  into  the  pulmonary  veins  is  thus  resisted,  rather  than  aided,  by 
the  force  generated  in  the  lungs. 

599.  The  change  in  the  condition  of  the  blood,  in  regard  to  the 
relative  proportions  of  its  oxygen  and  carbonic  acid,  is  the  only  one 
to  which  the  Pulmonary  circulation  is  subservient;  but  in  the  Sys- 
temic circulation,  the  changes  are  of  a  much  more  complex  nature, — 
every  distinct  organ  attracting  to  itself  the  peculiar  substances,  which 
it  requires  as  the  materials  of  its  own  nutrition,  and  the  nature  of  the 
affinities  thus  generated  being  consequently  different  in  each  case. 
But  the  same  law  holds  good  in  all  instances.  Thus  the  blood  con- 
veyed to  the  liver  by  the  portal  vein,  contains  the  materials  at  the 
expense  of  which  the  bile-secreting  cells  are  developed  ;  consequently 
the  tissue  of  the  liver,  which  is  principally  made  up  of  these  cells, 
possesses  a  certain  degree  of  affinity  or  attraction  for  blood  contain- 
ing these  materials ;  and  this  is  diminished,  so  soon  as  they  have  been 
drawn  from  it  into  the  cells  around.  Consequently  the  blood  of  the 
portal  vein  will  drive  before  it,  into  the  hepatic  vein,  the  blood  w^hich 
has  traversed  the  capillaries  of  the  portal  system,  and  which  has  given 
up,  in  doing  so,  the  elements  of  bile  to  the  solid  tissues  of  the  liver. 
— The  same  principle  holds  good  in  every  other  case. 

600.  We  are  now  prepared,  therefore,  to  understand  the  general 
principle,  that  the  rapidity  of  the  circulation  of  a  part  will  depend  in 
great  measure  upon  the  activity  of  the  functional  changes  taking  place 
in  it, — the  heart's  action,  and  the  state  of  the  general  circulation,  re- 
maining the  same.  When,  by  the  heightened  vitality,  or  the  unusual 
exercise,  of  a  part,  the  changes  which  the  blood  naturally  undergoes 
in  it  are  increased  in  amount,  the  affinities  which  draw  the  arterial 
blood  into  the  capillaries  are  stronger,  and  are  more  speedily  satisfied, 
and  the  venous  blood  is  therefore  driven  out  with  increased  energy. 
Thus  a  larger  quantity  of  blood  will  pass  through  the  capillaries  of  the 
part  in  a  given  time,  without  any  enlargement  of  their  calibre,  and 
even  though  it  be  somewhat  diminished  ;  but  the  size  of  the  arteries 
by  which  it  is  supplied,  soon  undergoes  an  increase,  which  adapts  it 
to  supply  the  increased  demand.  Any  circumstance,  then,  which  in- 
creases the  functional  energy  of  a  part,  or  stimulates  it  to  increased 
nutrition,  will  occasion  an  increase  in  the  supply  of  blood,  altogether 
irrespectively  of  any  change  in  the  heart's  action.  This  principle  has 
long  been  known,  and  has  been  expressed  in  the  concise  adage  "  Ubi 
stimulus,  ibi  fluxus;"  which  those  Physiologists,  who  maintain  that 
the  Circulation  is  maintained  and  governed  by  the  heart  alone,  cast 
into  unmerited  neglect. 

601.  An  undue  acceleration  of  the  local  circulation,  arising  from  an 


348      CIRCUMSTANCES  INFLUENCING  CAPILLARY  CIRCULATION. 

excess  of  functional  activity  in  the  part,  and  unaccompanied  by  any 
other  change,  constitutes  the  state  known  as  active  congestion,  or  deter- 
mination of  blood.  This  may  be  artificially  produced  by  the  applica- 
tion of  gentle  stimulants;  and  it  is  usually  the  first  change  that  occurs, 
when  their  action  proves  sufhciently  violent  to  produce  inflammation. 
From  that  state,  how^ever,  it  is  distinguished  by  this  important  charac- 
ter,— that  there  is  merely  an  exaltation  of  the  natural  function,  but  no 
change.  Moreover  we  shall  presently  see  that,  in  Inflammation,  there 
is  a  stagnation  of  blood,  not  an  acceleration.  We  frequently  meet 
with  cases,  in  which  this  active  congestion  becomes  very  manifest ; 
especially  in  persons  of  active  minds,  who  exert  their  mental  powers 
too  violently,  and  who  thereby  induce  an  habitually  increased  flow  of 
blood  towards  the  head,  manifested  in  the  increased  pulsation  of  the 
carotids,  the  suflfusion  of  the  face  and  eyes,  and  the  heat  of  the  surface. 
The  balance  of  the  circulation  being  thus  disturbed,  there  is  almost 
invariably  a  diminished  energy  of  the  movement  of  blood  in  other 
organs,  especially  the  extremities;  as  indicated  by  their  habitual  cold- 
ness and  lividity.  In  the  treatment  of  such  a  state  (which  is  often  the 
precursor  of  serious  disease),  it  should  be  our  object  to  restore  the  cir- 
culation in  the  extremities,  by  friction,  exercise,  &c.  ;  and  to  abate 
the  flow  of  blood  towards  the  head,  by  restraining  the  functional 
activity  of  the  brain,  by  the  application  of  cold  to  the  surface,  by 
keeping  the  head  high  during  sleep,  and  other  means  of  similar 
tendency. 

602.  There  is  another  condition  of  the  capillary  circulation,  also 
known  under  the  name  of  Congestion,  which  is  precisely  the  opposite 
of  the  preceding.  In  this  state,  there  is  deficient  functional  energy  in 
the  part  and  the  circulation  through  it  is  consequently  retarded, — as 
in  the  lungs,  when  there  is  a  partial  obstruction  to  the  aeration  of  the 
blood.  The  same  cause  produces  a  deficient  tonicity  of  the  Arteries, 
and  allows  their  walls  to  be  unduly  distended  by  the  vis  a  iergo  of  the 
blood  ;  and  consequently  there  is  a  great  accumulation  of  blood  in  the 
part  with  a  retarded  movement.  This  condition,  like  the  preceding, 
predisposes  to  Inflammation,  although  in  a  different  mode,  as  will  be 
explained  hereafter  (§  631).  It  is  relieved  by  causes  which  promote 
the  action  of  the  part ;  thus  congestion  of  the  lungs,  occasioned  by  the 
effusion  of  fluid  into  the  air-cells,  which  creates  an  obstacle  to  the  aera- 
tion of  the  blood  disappears,  when  that  effiision  is  absorbed.  And 
congestion  of  the  liver,  the  result  of  deficient  secreting  power  in  the 
organ,  is  relieved  by  mercurial  and  other  medicines,  which  promote  the 
flow  of  bile  by  stimulating  the  growth  of  the  hepatic  cells. 

603.  The  Capillaries,  like  the  Arteries,  possess  a  power  of  contrac- 
tion and  dilatation  w^hich  seems  to  be  very  much  under  the  influence 
of  the  Nervous  System,  and  particularly  of  that  part  of  it  which  con- 
veys the  influence  of  the  Emotions.  We  have  a  visible  example  of 
this  influence,  in  the  act  of  Blushing;  which  consists  in  a  sudden 
enlargement  of  the  capillaries  and  small  vessels  of  the  surface  ;  whilst 
the  converse  state  of  pallor^  which  often  alternates  with  it  under  the 


MOVEMENT  OF  BLOOD  IN  CAPILLARIES  AND  VEINS.  349 

influence  of  strong  emotion,  is  evidently  due  to  an  unusual  contraction 
of  the  same  vessels.  But  the  effects  of  this  influence  are  no  less  sen- 
sible in  other  cases;  and  particularly  in  the  regulation  of  the  quantity 
of  certain  secretions,  in  accordance  with  the  mental  state,  or  the  con- 
dition of  the  system  generally.  To  the  mode  in  which  this  regulation 
is  effected,  the  act  of  blushing  seems  to  afford  us  the  key  ;  for  it  indi- 
cates that  the  supply  of  blood  afforded  to  the  glands,  may  be  entirely 
governed  by  the  influence  of  the  nervous  system  upon  the  calibre  of 
the  arteries.  Thus,  the  nursing  mother,  at  the  sight,  or  even  at  the 
thought  of  her  child,  when  the  usual  time  for  suckling  approaches, 
feels  a  rush  of  blood  to  the  breast,  exactly  resembling  that  which  takes 
place  to  the  cheeks  in  blushing,  and  popularly  termed  "  the  draught ;" 
this  rush  occasions  an  almost  immediate  increase  in  the  secretion.  In 
like  manner  we  may  explain  the  influence  of  the  mental  state  upon  the 
amount  of  the  secretions  of  the  lachrymal,  the  salivary  and  many  other 
glands ;  its  influence  upon  their  quality^  must  probably  be  effected 
through  changes  in  the  condition  of  the  blood  itself. 

604.  The  supply  of  Nervous  agency  from  the  Cerebro-spinal  system 
has  been  clearly  proved  to  exert  no  direct  influence  in  maintaining  the 
capillary  circulation;  since  the  latter  continues  as  usual,  after  all  the 
nerves  of  a  part  have  been  divided.  This  is  obviously  due  to  the  fact, 
that  the  operations  of  nutrition,  secretion,  &c.,  are  essentially  inde- 
pendent of  this  agency.  But  as  they^xe  in  some  degree  injluenced  by 
it,  so  will  the  capillary  circulation  be  affected  through  its  connection 
with  them.  In  this  manner  we  are  to  explain  the  effect  of  violent 
impressions  upon  the  nervous  centres  in  bringing  to  a  stand,  not 
merely  the  action  of  the  heart  (§  581),  but  the  Capillary  circulation 
all  over  the  body.  The  general  vitality  of  the  system  appears  to  be 
at  once  destroyed  ;  so  that  the  capillary  circulation,  which  may  usually 
be  seen  to  continue  in  the  web  of  a  frog's  foot  for  some  time  after  the 
interruption  of  the  heart's  action,  is  immediately  suspended  by  crush- 
ing the  brain  with  a  hammer. 

6.   Of  the  movement  of  Blood  in  the  Veins, 

605.  The  Venous  system  is  formed  by  the  reunion  of  the  small 
trunks  which  originate  in  the  Capillary  network;  and  it  carries  back 
to  the  heart  the  blood  which  has  been  transmitted  through  this.  This 
blood  is  dark  or  carbonated  in  the  systemic  veins ;  whilst  it  is  bright  or 
oxygenated  in  the  pulmonary  veins. — The  structure  of  the  veins  is 
essentially  the  same  with  that  of  the  arteries ;  but  the  fibrous  tissue  of 
their  middle  coat  less  decidedly  exhibits  the  characters,  either  of  the 
yellow  elastic  tissue,  or  of  non-striated  muscle.  Still  it  possesses  no 
inconsiderable  amount  of  Elasticity;  and  a  certain  degree  of  mus- 
cular Contractility  also.  The  whole  capacity  of  the  Venous  system  is 
at  least  twice^  and  perhaps  more  nearly  three  times,  that  of  the  Arte- 
rial ;  and  the  rate  of  motion  of  the  blood  in  them  must  be  propor- 
tionably  slower. 


330 


RESPIRATORY  PULSE. 


606.  The  movement  of  the  Blood  through  the  Veins  is,  without 
doubt,  chiefly  effected  by  the  vis  a  tergo,  or  propulsive  force,  which 
results  from  the  contractile  power  of  the  heart  and  arteries,  aided  by 
the  power  generated  in  the  capillary  vessels.  The  intermittent  flow, 
which  is  caused  by  the  interrupted  action  of  the  former  is  usually  so 
far  equalized  during  the  passage  of  the  blood  through  the  capillary 
network,  that  no  pulsation  can  be  shown  to  exist  in  the  veins  ;  but  in- 
stances occasionally  present  themselves,  in  which  a  venous  pulse  may 
be  clearly  perceived. — The  Venous  Circulation  is  affected,  however, 
by  certain  other  causes  which  exert  little  influence  on  the  movement  of 
blood  in  the  Arteries.  One  of  these  is  the  frequently  recurring  action 
of  Muscles,  to  which  the  Veins  are  peculiarly  subject,  on  account  of 
Iheir  position.  In  every  instance  in  which  Muscular  movement  takes 
place,  a  portion  of  the  Veins  of  the  part  will  undergo  compression ; 
;ind  as  the  blood  is  prevented  by  the  valves  in  the  veins,  from  being 
driven  back  into  the  small  vessels,  it  is  necessarily  forced  onwards 
towards  the  heart.  As  each  set  of  muscles  is  relaxed,  the  veins  that 
were  compressed  by  it  fill  out  again,  to  be  again  compressed  on  the 
renewal  of  the  force.  Thus,  we  see  how  the  general  Muscular  move- 
ments of  the  body  have  an  important  influence,  in  maintaining  the 
Venous  Circulation, — how  continued  exercise,  involving  the  alternate 
contraction  and  relaxation  of  several  groups  of  Muscles,  must  send  the 
blood  more  rapidly  towards  the  heart,  and  thus  increase  the  rapidity 
of  its  pulsations, — and  how  the  sudden  and  simultaneous  action  of  a 
large  number  of  muscles  after  repose  (as  when  we  rise  up  from  the 
sitting  or  lying  to  the  standing  posture),  may  drive  the  blood  to  the 
heart  with  so  violent  an  impetus  as  to  produce  even  fatal  results,  if, 
by  any  diseased  condition  of  that  organ,  it  should  be  rendered  unable 
to  dispose  with  sufficient  rapidity,  of  the  quantity  of  blood  thus  driven 
to  it. 

607.  The  Respiratory  movements  exert  a  slight  influence  upon  the 
flow  of  blood  through  the  large  veins  near  the  heart ;  for  as  the  chest 
is  a  closed  cavity,  in  which  a  partial  vacuum  is  produced  by  the  act 
of  Inspiration,  whilst  its  contents  are  compressed  by  the  act  of  Expi- 
ration, the  former  state  will  favour  the  movement  of  blood  from  the 
large  veins  on  the  exterior  of  the  cavity,  towards  the  heart,  whilst  the 
latter  condition  will  retard  it.  This  produces  the  phenomenon  termed 
the  respiratory  pulse;  which  may  be  seen  in  the  veins  of  the  neck  and 
shoulders  in  thin  persons,  and  especially  in  those  who  are  suffering 
from  pulmonary  diseases.  The  influence  of  the  Respiratory  move- 
ments is  made  evident  by  introducing  a  tube  into  the  Jugular  vein, 
the  lower  end  of  which  dips  into  water  ;  for  an  alternate  elevation  and 
depression  of  the  water  in  the  tube  are  then  witnessed,  showing  the 
suction  power  of  the  Inspiratory  movement,  and  the  expellent  force  of 
the  Expiratory  act.  On  the  other  hand,  the  Expiratory  movement, 
while  it  directly  tends  to  cause  accumulation  in  the  veins,  will  assist 
the  heart  in  propelling  the  blood  in  the  Arteries ;  and  by  the  com- 
bined action  of  these  two  causes  are  produced,  among  other  effects, 


I 


VENOUS  CONGESTION.— INFLUENCE  OF  GRAVITY.  351 

the  rising  and  sinking  of  the  Brain,  synchronously  with  expiration 
and  inspiration,  which  are  observed  when  a  portion  of  the  cranium 
is  removed. 

608.  A  pulsatory  movement  may  be  occasioned  in  the  great  vems 
near  the  heart,  by  another  cause  entirely  distinct  from  the  preceding  ; 
— namely,  the  regurgitation  of  blood  from  the  ventricle  into  the  auri- 
cle, and  thence  into  the  vense  cavse,  during  the  ventricular  systole  ; 
and  the  pulsation  thus  occasioned  is  synchronous,  therefore,  with  that 
in  the  arteries  (proceeding  backwards^  however,  from  the  heart),  in- 
stead of  corresponding  with  the  respiratory  movement.  This  regurg- 
itation may  take  place,  not  from  any  disease  in  the  valves  on  the  right 
side  of  the  heart,  but  simply  from  over-distension  of  its  cavities,  re- 
sulting from  any  obstruction  to  the  circulation  of  blood  through  the 
lungs,  for  when  this  occurs,  the  tricuspid  valve  does  not  completely 
close,  and  allows  a  portion  of  the  blood  to  escape  from  the  ventricle 
backwards  into  the  auricle  and  vena  cava.  This  want  of  complete 
closure,  effecting  what  has  been  termed  the  "  safety-valve  function" 
of  the  tricuspid  valve,  has  been  particularly  noticed  in  diving  animals, 
in  which  the  circulation  through  the  lungs  is  liable  to  be  temporarily 
suspended.  The  venous  pulsation  which  is  thus  produced  may  be 
noticed  in  almost  every  case  of  long-standing  dyspnoea ;  especially 
when  this  is  accompanied  (as  it  usually  is)  by  hypertrophy  and  dilata- 
tion of  the  right  ventricle  of  the  heart. 

609.  The  Venous  circulation  is  much  more  liable  than  the  Arterial, 
to  be  influenced  by  the  force  of  Gravity ;  and  this  influence  is  par- 
ticularly noticeable,  when  the  tonicity  of  the  vessels  is  deficient.  The 
following  experiments  performed  by  Dr.  Williams,  to  elucidate  the 
influence  of  deficient  firmness  in  the  walls  of  the  vessels,  and  of 
gravitation,  over  the  movement  of  fluids  through  tubes,  throw  great 
light  on  the  causes  of  Venous  Congestion.  A  tube  with  two  equal 
arms  having  been  fitted  to  a  syringe,  a  brass  tube  two  feet  long,  hav- 
ing several  right  angles  in  its  course,  was  adapted  to  one  of  them, 
whilst  to  the  other  was  tied  a  portion  of  a  rabbit's  intestine  four  feet 
long,  and  of  calibre  double  that  of  the  brass  tube,  this  being  arranged 
in  curves  and  coils,  but  without  angles  and  crossings.  When  the  two 
ends  were  raised  to  the  same  height,  the  small  metal  tube  discharged 
from  two  to  five  times  the  quantity  of  water  discharged  in  a  given  time 
by  the  larger  but  membranous  tube;  the  difference  being  greatest,  when 
the  strokes  of  the  piston  were  most  forcible  and  sudden,  by  which 
the  intestine  was  much  dilated  at  its  syringe  end,  but  conveyed  very 
little  more  water.  When  the  discharj^ino:  ends  were  raised  a  few 
inches  higher,  the  difference  increased  considerably,  the  amount  of 
fluid  discharged  by  the  gut  being  much  diminished  ;  and  when  the 
ends  were  raised  to  the  height  of  eight  or  ten  inches,  the  gut  ceased 
to  discharge,  each  stroke  only  moving  the  column  of  water  in  it,  and 
this  subsiding  again,  without  rising  high  enough  to  overflow.  When 
the  force  of  the  stroke  was  increased,  the  part  of  the  intestine  nearest 
the  syringe  burst. 


352  CIRCULATION  WITHIN  THE  CRANIUM. 

610.  From  these  experiments  it  is  easy  to  understand,  how  any 
deficiency  of  tone  in  the  Venous  system  will  tend  to  prevent  the  ascent 
of  the  blood  from  the  depending  parts  of  the  body,  and  will  conse- 
quently occasion  an  increased  pressure  on  the  walls  of  the  vessels, 
and  an  augmentation  in  the  quantity  of  blood  they  contain.  All  these 
conditions  are  peculiarly  favourable  to  the  escape  of  the  watery  part 
of  the  blood  from  the  small  vessels  ;  and  this  may  either  infiltrate  into 
the  areolar  tissue,  or  it  may  be  poured  into  some  neighbouring  serous 
cavity,  producing  dropsy.  Thus  it  happens,  that  such  eflfusions  may 
often  be  traced  to  that  state  of  deficient  vigour  of  the  system,  which 
peculiarly  manifests  itself  in  want  of  tone  of  the  blood-vessels  ;  and 
that  it  is  relieved  by  remedies  which  tend  to  restore  this.  In  many 
young  females  of  leucophlegmatic  temperament,  for  example,  there 
is  a  tendency  to  swelling  of  the  feet,  by  cedematous  effusion  into  the 
areolar  tissue,  in  consequence  of  the  depending  position  of  the  limbs; 
the  oedema  disappears  during  the  night,  but  returns  during  the  day, 
and  is  at  its  maximum  in  the  evening.  And  the  congestion  which 
frequently  manifests  itself  in  the  posterior  parts  of  the  body,  towards 
the  close  of  exhausting  diseases,  in  which  the  patient  has  lain  much 
upon  his  back,  is  attributable  to  a  similar  cause  ;  of  such  congestion, 
effusions  into  the  various  serous  cavities  are  frequent  results ;  and 
such  effusions  taking  place  during  the  last  hours  of  life,  are  often 
erroneously  regarded  as  the  cause  of  death.  To  the  same  cause  we 
are  to  attribute  the  varicose  state  of  the  veins  of  the  leg,  which  is  so 
common  amongst  persons  of  relaxed  fibre,  and  especially  in  those 
whose  habits  require  them  to  be  much  in  the  erect  posture ;  and  this 
distension  occasionally  proceeds  to  complete  rupture,  the  causes  of 
which  are  fully  elucidated  by  the  experiments  just  cited. 

611.  It  has  been  thought  that  the  circulation  within  the  Cranium 
takes  place  under  different  conditions  from  that  of  other  parts  of  the 
body.  For  as  the  cranium  is  a  closed  cavity, — a  certain  part  of  which 
is  occupied  by  the  cerebral  substance  and  its  membranes,  the  remain- 
der being  filled  up  with  blood, — it  has  been  argued  that  the  amount 
of  blood  in  the  vessels  of  the  brain  must  be  always  the  same;  and 
that  any  disturbance  of  its  circulation  must  be  due  to  a  difference  in 
the  relative  quantity  of  blood  in  the  arteries  and  the  veins.  This 
idea  appeared  to  derive  support  from  the  results  of  experiments ; 
which  showed  that  the  blood  is  retained  in  the  vessels  within  the 
cranium  of  animals  bled  to  death,  unless  an  opening  be  made  in  the 
skull,  so  as  to  allow  the  air  to  exert  the  same  pressure  upon  these 
vessels,  as  upon  those  of  other  parts.  But  such  experiments  do  not 
at  all  sanction  the  assertion,  that  the  quantity  of  blood  within  the 
cranium  is  constant ;  on  the  contrary,  we  have  reason  to  believe  that 
it  undergoes  as  much  change  as  in  other  parts.  For  although  the 
cerebral  substance  be  incompressible,  yet  its  bulk  is  subject  to  con- 
stant variation,  according  to  the  quantity  of  fluid  it  contains;  and  the 
presence  of  the  cerebro-spinal  fluid  in  the  sub-arachnoid  cavity  in  the 
brain  and  spinal  cord,  appears  to  be  peculiarly  destined  to  favour  this 


I 


MATERIALS  OF  THE  NUTRITIVE  PROCESS.  353 

continual  change, — the  proportions  of  it  contained  in  the  spinal  and 
cerebral  cavities,  respectively,  being  governed  by  the  bulk  of  the 
other  contents  of  the  cranium.  Thus  if  the  vessels  of  the  cerebrum 
be  in  their  ordinary  state  of  fullness,  a  certain  amount  of  fluid  is  pre- 
sent in  the  sub-arachnoid  cavity  of  the  brain  ;  this  will  be  pressed  out 
into  the  spinal  portion  of  the  cavity,  if  the  cerebral  vessels  be  unusu- 
ally distended  with  blood  ;  whilst  it  will  be  increased  from  the  latter 
source,  so  as  to  fill  up  the  vacant  space  within  the  cranium,  if  the 
cerebral  vessels  be  unusually  empty. 


CHAPTER  VII. 

OF  NUTRITION. 

1.  Selecting  power  of  the  Individual  Parts. 

612.  The  Blood,  which  is  carried  into  the  different  parts  of  the 
system,  by  the  Circulating  apparatus,  is  the  source  from  which  all  the 
organs  and  tissues  of  the  body  derive  the  materials  of  their  growth 
and  development;  and,  as  we  have  seen,  it  is  distributed  by  the  Ca- 
pillaries of  the  several  tissues,  with  a  degree  of  minuteness,  which 
varies  according  to  the  activity  of  the  nutrient  operations  taking  place 
in  the  individual  parts.  Thus,  in  Nerve  and  Muscle,  Mucous  Mem- 
brane, and  Skin,  a  constant  decay  of  the  old,  and  development  of  new 
tissue,  are  taking  place,  when  these  organs  are  in  a  state  of  functional 
activity  ;  and  a  copious  supply  of  blood  is  carried  through  every  part 
of  their  substance  :  whilst  in  Cartilage  and  Bone,  Tendon  and  Liga- 
ment, the  amount  of  interchange  is  very  small,  and  is  effected  by  a 
much  less  minute  reticulation  of  capillary  blood-vessels. 

613.  The  materials  of  the  nutritive  process  being  prepared  in  the 
blood,  the  process  of  Nutrition  is  the  act  of  each  individual  part ; 
which  grows  and  develops  itself,  in  virtue  of  its  own  inherent 
powers,  as  long  as  the  requisite  conditions  are  supplied.  The  mode 
in  which  this  takes  place,  in  each  individual  tissue,  has  been  already 
explained  in  the  former  part  of  this  Treatise.  We  have  seen  that,  in 
the  great  majority  of  cases,  the  act  of  Nutrition  is,  in  fact,  a  process 
of  cell-growth  ;  and  that  it  takes  place  under  the  same  conditions,  as 
the  production  of  the  simple  isolated  cell,  which  constitutes  the 
whole  of  the  humblest  forms  of  Cryptogamic  Vegetation, — namely, 
that  it  grows  from  a  germ,  which  draws  to  itself  the  materials  of  its 
nutrition,  and  gives  to  some  of  them  a  new  arrangement,  whereby 
they  form  the  cell-wall,  whilst  others  are  introduced  into  the  cell- 
cavity, — and  that,  when  it  has  passed  through  its  regular  series  of 
changes,  it  dies,  and  sets  free  its  contents.     We  have  seen  that,  in 

23 


354  SYMMETRY  OF  THE  NUTRITIVE  PROCESSES. 

some  cases,  the  germs  are  prepared  by  previously  existing  cells  of 
the  same  kind  ;  whilst  in  others  they  are  furnished  by  certain  "  nutri- 
tive centres,"  which  seem  to  be  constantly  engaged  in  the  preparation 
of  them,  deriving  their  materials  from  the  blood.  Frequently  it  would 
seem  as  if  the  original  or  parent-cell  was  able  to  continue  the  pro- 
duction of  secondary  cells  to  an  unlimited  extent,  even  though  it  has 
itself  undergone  a  considerable  change  of  form.  Thus  the  ultimate 
follicles  of  Glands  seem  to  be  at  first  closed  cells,  which  subsequently 
open  at  the  part  nearest  to  the  .duct,  and  establish  a  connection 
with  it ;  and  having  thus  changed  their  condition,  they  go  on  deve- 
loping new  generations  of  secreting-cells  in  their  interior,  from  their 
own  nuclei  or  germinal  centres,  to  an  unlimited  extent.  In  like 
manner,  the  parent-cells  of  Muscular  Fibre,  which  have  coalesced  to 
form  the  tubular  Myolemma,  seem  to  continue  to  develop  new  fibrillse 
from  their  nuclei,  notwithstanding  their  change  of  form. 

614.  The  selecting  power,  which  is  possessed  by  the  germs  of  each 
kind  of  tissue,  and  which  enables  them  to  draw  from  the  blood  the 
materials  which  they  severally  require  for  their  development,  mani- 
fests itself  also  in  the  mode  in  which  substances,  that  are  abnormally 
present  in  the  blood,  affect  the  condition  and  development  of  the 
solid  tissues.  Thus  we  find  that  the  presence  of  a  certain  quantity 
of  Arsenic  in  the  blood,  will  produce  a  state  of  irritation  in  all  the 
Mucous  membranes  of  the  body.  The  continued  introduction  of  Lead 
into  the  circulating  system,  occasions  a  modification  in  the  nutrition 
of  the  extensor  muscles  of  the  fore-arm,  producing  the  form  of  partial 
paralysis  commonly  termed  wrist-drop;  and  the  existence  of  this 
modification  is  shown,  by  the  presence  of  lead  in  the  palsied  muscles. 
Here  we  have  to  remark  the  symmetrical  nature  of  the  affection,  con- 
sequent upon  the  occurrence  of  the  same  disorder  in  the  corresponding 
parts  of  the  two  sides  of  the  body;  for  these  muscles  appear  to  have 
the  same  kind  of  tendency  to  attract  lead  from  the  circulating  current, 
in  a  degree  that  is  equal  on  the  two  sides,  as  they  have  to  draw  from 
the  blood  the  materials  of  their  regular  growth,  and  to  develop  them- 
selves in  an  exactly  similar  manner.  In  like  manner,  the  cutaneous 
eruptions,  which  are  occasionally  produced  by  the  internal  exhibition 
of  iodide  of  potassium,  are  found  to  be  almost  precisely  symmetrical; 
the  presence  of  the  medicine  in  the  blood  being  the  occasion  of  a 
disordered  nutrition  of  certain  parts  of  the  skin ;  and  the  selecting 
power  of  particular  spots  being  evinced,  by  the  exact  correspondence 
of  the  parts  affected  on  the  two  sides. 

615.  The  same  appears  to  be  the  case  with  regard  to  substances, 
w^hose  presence  in  the  blood  is  rather  the  result  of  a  disordered  con- 
dition of  the  digestive  and  assimilating  processes,  than  of  their  direct 
introduction  from  without.  Thus  in  Lepra  and  Psoriasis, — chronic 
diseases  of  the  Skin,  which  seem  to  have  their  origin  in  a  disordered 
state  of  the  blood,  rather  than  in  the  solid  tissues  affected, — we  find  a 
remarkable  tendency  to  the  repetition  of  the  patches,  on  the  two  sides 
of  the  body,  or  on  the  corresponding  parts  of  the  limbs ;  and  this  we 


> 


I 


UNUSUAL  ENERGY  OF  THE  NUTRITIVE  PROCESSES.  355 

must  attribute  to  the  peculiar  attraction,  existing  between  the  solid 
tissues  of  those  parts,  and  the  morbid  matter  circulating  through  them. 
So  in  those  chronic  forms  of  Gout  and  Rheumatism,  which  modify 
the  nutrition  of  the  joints,  producing  a  deposit  of  *^  chalk-stones,"  or 
permanent  distortion  and  stiffening,  we  almost  invariably  find  the 
corresponding  joints  of  the  two  sides  affected.  The  chief  exceptions 
to  the  general  principle,  that  the  presence  of  morbid  or  extraneous 
matters  in  the  blood  affects  corresponding  parts  alike,  are  found  to 
exist  where  there  is  much  febrile  disturbance,  or  where  local  causes 
produce  a  peculiar  tendency  to  disorder  of  a  single  part.  The  nearer 
the  character  of  the  morbid  process  is  to  that  of  the  ordinary  nutritive 
operations,  the  more  nearly  does  it  approach  these,  in  the  symmetry 
with  which  it  develops  itself.* 

2.   Varying  Activity  of  the  JVutritive  Processes. 

616.  The  nutritive  operations  go  on  with  very  great  variations  in 
their  relative  activity,  under  different  circumstances.  As  a  general 
rule  it  may  be  stated  that,  the  greater  the  demand  for  the  functional 
activity  of  the  organ  or  tissue,  the  more  energetic  is  its  nutrition  ;  and 
vice  versa.  Now  this  is  readily  understood,  when  it  is  considered, 
that  the  active  state  of  many  structures  essentially  consists  in  an  act 
of  nutrition ;  thus  the  energy  of  the  secreting  processes  is  really  de- 
pendent, as  we  have  seen,  upon  the  growth  of  the  secreting  cells, 
which  make  up  the  essential  part  of  the  gland  ;  and  the  energy  of  the 
absorbing  and  assimilating  processes  is  dependent  upon  the  develop- 
ment of  the  cells,  which  select  and  elaborate  the  nutrient  matter. 
This  growth  is  regulated  mainly  by  the  supply  of  blood  ;  being 
increased  by  the  afflux  of  blood  towards  the  part,  in  consequence  of 
the  influence  of  the  nerves  upon  the  vessels,  or  through  any  other 
change  in  the  current  of  the  circulation.  Thus  the  secretions  are 
increased  in  amount,  by  emotions  of  the  mind,  that  act  (probably 
through  the  sympathetic  nerve),  in  regulating  the  calibre  of  the  arteries 
supplying  their  respective  glands;  or  the  interruption  of  the  function 
of  one  gland  shall  occasion  an  increased  nutrition,  and  consequently 
an  augmented  secretion,  in  its  fellow, — as  when  one  of  the  kidneys 
is  hypertrophied,  through  a  disease  in  the  other,  that  renders  it  inca- 
pable of  performing  its  office.  Still  it  would  appear,  that  there  may 
be  variations  in  the  activity  of  these  organs,  resulting  fram  causes 
inherent  in  themselves  (of  the  nature  of  which  we  know  little  or 
nothing);  and  that  here,  as  elsewhere,  active  nutritive  operations  will 
promote  the  circulation  of  blood  through  the  parts,  whilst  a  languid 
state  of  the  function  will  retard  it. 

617.  In  certain  other  tissues,  however,  the  functional  activity  would 
seem  to  be  dependent  rather  upon  a  waste  or  decay  of  structures  pre- 
viously developed  ;  this  is  the  case  especially  in  Nerve  and  Muscle, 

•  See  Dr.  W.  Budd's  valuable  paper  on  the  "Symmetry  of  Disease,"  in  vol.  xxv.  of 
the  Medico-Chirurgical  Transactions. 


356  VARIOUS  CAUSES  OF  HYPERTROPHY. 

which  are  found  to  undergo  disintegration,  in  exact  proportion  to  the 
degree  in  which  they  are  exercised;  whilst  the  degree  in  which  this 
waste  is  repaired,  depends  upon  the  supply  of  nutritive  material,  the 
quiescent  state  of  the  part,  and  other  circumstances.  But  even  here 
we  find,  that  functional  activity  occasions  increased  nutrition ;  in  the 
same  manner  as  burning  a  lamp  with  a  high  flame  increases  the 
amount  of  fluid  drawn  up  by  the  wick.  For  neither  the  nerves  nor 
the  muscles  can  act  with  energy,  without  a  large  supply  of  arterial 
blood ;  and  this  is  drawn  to  them  on  the  principles  already  mentioned, 
as  increasing  the  energy  of  the  local  circulation  (§  600).  The  deter- 
mination of  blood  to  the  parts,  thus  established,  favours  their  increased 
nutrition ;  and  thus  we  find  that,  under  favourable  circumstances, 
any  set  of  Muscles,  which  is  habitually  exercised,  undergoes  a  great 
increase  of  development;  whilst,  in  like  manner  the  Nervous  centres, 
if  too  great  a  demand  be  made  upon  their  activity,  are  liable  to 
become  hypertrophied  (especially  in  young  persons),  and  may  thus 
become  subject  to  disorders,  which  temporarily  or  permanently  de- 
stroy their  powers.  In  these  cases,  then,  the  functional  activity 
determines  the  increased  supply  of  blood,  and  occasions  the  aug- 
inented  growth  ;  and  increased  nutrition  will  rarely  take  place  in 
these  tissues,  without  an  especial  stimulus  of  this  kind.  Thus  we  find 
that,  when  a  larger  supply  of  nutritive  matter  is  introduced  into  the 
circulation,  than  is  required  to  repair  the  waste  of  these  tissues,  they 
do  not  undergo  an  increased  development  in  consequence  ;  but  an 
augmented  nutrition  is  produced,  either  in  the  adipose  tissue,  or  in 
the  glandular  structures  by  which  the  superfluous  matter  is  eliminated 
from  the  system. 

618.  Augmented  nutrition,  or  Hypertrophy^  then,  may  result,  in 
certain  organs,  from  an  excessive  supply  of  their  nutrient  materials ; 
as  in  the  case  of  the  kidney  just  mentioned ;  or  as  in  the  enlargement 
which  we  not  unfrequently  meet  with  in  the  livers  of  those  who  have 
resided  long  in  warm  climates,  and  who  have  not  suflSciently  restricted 
their  supply  of  non-azotized  food  to  the  small  amount  required  for 
respiration  at  an  elevated  temperature,  thereby  sending  an  over-sup- 
ply of  that  particular  class  of  bodies,  to  be  separated  from  the  blood 
by  the  liver.  Or,  in  other  cases,  the  increase  of  functional  activity 
may  be  the  immediate  cause  of  the  increased  nutrition  ;  and  this  we 
see,  not  only  in  the  nervous  centres  and  voluntary  muscles,  which 
are  put  in  action  by  the  will,  but  in  parts  over  which  the  mind  has 
no  control.  Thus  the  heart  becomes  hypertrophied,  when  an  obstruc- 
tion exists  in  the  pulmonary  or  systemic  circulation,  to  overcome 
which,  increased  energy  of  contraction  is  required  ;  and  in  the  same 
manner,  the  muscular  coats  of  the  urinary  and  gall-bladders  acquire 
an  extraordinary  increase  of  thickness,  when  long-continued  obstruc- 
tion, by  calculi  or  stricture  in  the  canals  issuing  from  them,  impedes 
the  free  exit  of  their  contents.  Sometimes,  however,  a  local  hyper- 
trophy takes  place,  which  cannot  be  accounted  for  in  either  of  these 
modes ;  as  when  a  single  finger  is  enlarged  out  of  all  proportion  to 


VARIOUS  CAUSES  OF  ATROPHY.  357 

the  rest,  or  the  whole  of  one  hand  increases  to  a  much  greater  size 
than  the  other,  by  the  existence  (as  it  would  seem)  in  the  individual 
part,  of  that  tendency  to  unusual  development,  which,  when  it  affects 
the  whole  body  uniformly,  produces  a  gigantic  stature. 

619.  Now  a  precisely  reversed  series  of  conditions  diminishes  the 
activity  of  the  nutrient  processes,  and  induces  a  state  of  Atrophy.  If 
there  be  a  deficiency  in  the  general  amount  of  nutriment  introduced 
into  the  system  by  absorption,  2, general  atrophy  results;  and  the  waste 
being  more  rapid  than  the  supply,  there  is  a  diminution  in  the  volume 
of  all  the  tissues  excepting  the  nervous,  which  seems  to  have  its  nu- 
trition kept  up  even  to  the  last,  at  the  expense  of  all  the  rest.  Such 
a  condition  results  not  merely  from  the  want  of  food,  but  also  from 
the  want  of  power  to  assimilate  it ;  and  thus  emaciation  may  take  place 
to  an  excessive  degree,  when  food  of  the  most  nutritive  character  is 
copiously  applied,  and  when  the  appetite  for  it  is  vehement;  in  con- 
sequence of  disorder  in  the  mesenteric  glands,  or  in  some  other  part 
of  the  apparatus  particularly  concerned  in  the  elaboration  of  fibrin.  A 
partial  atrophy  may  result,  in  like  manner,  from  a  deficiency  of  the 
materials  required  for  the  formation  of  an  individual  tissue  or  organ  ; 
thus  the  adipose  tissue,  throughout  the  body,  may  be  atrophied,  in 
consequence  of  an  absence  of  those  materials  in  the  food,  which  are 
capable  of  being  converted  into  fatty  matter.  Or  a  particular  organ 
may  be  atrophied,  by  a  diminution  of  the  circulating  current  that 
should  flow  to  it,  either  in  consequence  of  obstruction  in  the  trunk, 
or  by  the  partial  diversion  of  the  stream  of  blood  in  another  direc- 
tion ;  thus  the  liver,  which  is  much  more  developed  in  the  fcetus, 
relatively  to  the  rest  of  the  body,  than  it  is  in  the  adult,  undergoes  a 
partial  atrophy  immediately  after  birth,  in  consequence  of  the  change 
in  the  whole  course  of  the  circulation,  which  takes  place  as  soon  as 
the  lungs  are  expanded. 

620.  But  partial  atrophy  may  also  take  place  from  causes  inherent 
in  a  particular  organ.  Thus  we  occasionally  meet  with  limbs,  which 
are  '^  blighted  ;"  never  attaining  their  due  size  relatively  to  the  re- 
mainder of  the  body;  yet  not  exhibiting  any  defect  of  organization. 
Here  there  would  seem  to  be,  from  some  unknown  cause,  a  deficient 
power  of  growth;  analogous  to  that  which,  w^hen  acting  on  the  body 
in  general,  confines  it  within  dwarfish  dimensions. — One  of  the  most 
frequent  causes  of  partial  atrophy,  however,  is  want  of  functional  ac- 
tivity in  the  organ ;  and  this  is  particularly  the  case  in  regard  to  the 
Muscular  and  Nervous  systems.  Thus,  as  already  remarked  (§  348), 
any  set  of  Muscles  that  is  long  disused,  becomes  partially  atrophied  ; 
which  is  probably  due  to  the  feebleness  and  languor  of  the  circula- 
tion, consequent  upon  the  absence  of  the  demand  for  arterial  blood. 
As  soon  as  the  parts  are  called  into  use  again,  their  nutrition  improves. 
So,  also,  in  regard  to  the  Nerves  ;  the  nutrition  of  both  the  fibrous 
and  vesicular  structures  appears  to  be  entirely  dependent  upon  the 
activity  of  their  function ;  and  as  the  former  are  inert  without  the  lat- 
ter, we  may  say  that  the  due  nutrition  of  the  nervous  system  entirely 


358  VARYING  ACTIVITY  OF  THE  NUTRITIVE  PROCESSES. 

depends  upon  the  functional  activity  of  the  vesicular  matter.  Of  this 
we  have  a  well-marked  illustration  in  the  fact,  that,  when  the  Cornea 
has  been  rendered  so  opaque  by  disease  or  accident,  as  to  prevent 
the  penetration  of  any  light  to  the  interior  of  the  eye,  the  retina  and 
the  optic  nerve  lose  after  a  time  their  characteristic  structure;  so  that 
scarcely  a  trace  of  the  peculiar  globules  of  the  former,  or  of  the  nerve- 
tubes  of  the  latter,  can  be  found  in  them. 

621.  In  the  healthy  condition  of  the  organism,  however,  the  nutri- 
tion of  every  part  of  the  body  goes  on  in  a  degree  sufficient  to  keep 
it  constantly  ready  for  the  performance  of  its  appropriate  function  ;  a 
regular  supply  of  the  requisite  materials  being  furnished  in  the  aliment, 
and  being  prepared  by  the  assimilating  processes ;  and  the  products 
of  the  waste  or  decay  of  the  tissues,  together  with  such  alimentary 
materials  as  maybe  superfluous,  being  carried  off  by  the  excreting 
operations.  When  the  nutrition  and  the  waste  are  equal,  the  weight 
of  the  body  remains  the  same  ;  and  this  is  commonly  the  case  in 
adult  age.  But  during  the  earlier  periods  of  life,  the  powers  of 
growth  are  greater ;  the  demand  for  food  is  very  large,  in  proportion 
to  the  bulk  of  the  body ;  and  though  the  waste  is  rapid  and  the  ex- 
creting processes  very  active  (as  evinced  by  the  large  amount  of  urea 
and  of  carbonic  acid  set  free),  the  growth  predominates  over  the 
decay,  and  the  development  of  the  whole  structure  proceeds  at  a  gra- 
dually decreasing  rate,  until  the  full  stature  and  bulk  are  attained. 
The  energy  of  the  nutritive  process  is  particularly  manifested  in  the 
rapidity  and  completeness  with  which  severe  injuries,  occasioned  by 
disease  or  accident,  are  repaired.  In  advanced  life,  on  the  contrary, 
although  the  waste  is  comparatively  small,  the  renewing  processes  are 
enfeebled  in  a  still  greater  degree ;  and  there  is  a  gradual  diminution 
in  the  stature  and  bulk  of  the  body,  and  in  its  physical  powers.  All 
the  functions  are  performed  with  diminished  energy ;  and  the  compa- 
rative inertness  of  the  nutritive  processes  is  seen  in  the  difficulty 
with  which  the  effects  of  severe  injuries  are  repaired,  in  the  length  of 
time  requisite  for  the  purpose,  and  frequently  in  the  imperfection  of 
the  result. 

622.  During  the  successive  periods  of  life,  there  are  many  remark- 
able changes  in  the  relative  nutrition  of  different  organs ;  which  we 
can  attribute  to  nothing  else  than  to  inherent  differences  in  their  own 
powers  of  development.  Thus,  during  the  early  stages  of  fcetal  exist- 
ence, the  greatest  energy  of  growth  is  seen  in  certain  parts,  which  are 
to  answer  but  a  temporary  purpose,  and  which  are  afterwards  com- 
pletely atrophied.  This  is  the  case,  for  example,  with  the  Corpora 
Wolffiana,  which  seem  to  answer  the  purpose  of  temporary  kidneys, 
and  in  connection  with  which  the  permanent  kidneys  and  the  genital 
organs  are  developed  ;  and  of  these  bodies,  though  of  large  size  in  the 
early  embryo,  and  evidently  of  great  importance,  no  trace  whatever  is 
afterwards  to  be  discovered.  So  in  regard  to  the  Supra-Renal  cap- 
sules, the  Thymus  and  Thyroid  glands,  and  other  organs,  we  find  their 
proportional  size  the  greatest,  and  their  function  evidently  the  most 


VARIATIONS  OF  NUTRITION  WITH  AGE.  359 

active,  during  fetal  existence  and  in  early  infancy ;  after  which  their 
bulk  diminishes  in  proportion  to  the  rest  of  the  body,  and  their  func- 
tional activity  seems  ahnost  at  an  end. 

623.  Even  in  the  relative  development  of  the  organs,  which  form 
essential  parts  of  the  permanent  structure,  we  find  considerable  varia- 
tions at  different  periods  of  life.  Thus  the  evolution  of  the  generative 
system  does  not  usually  take  place,  until  the  rest  of  the  system  is  ap- 
proaching its  maturity ;  but  cases  sometimes  occur,  in  which  this  appa- 
ratus attains  its  full  development,  both  in  the  male  and  the  female, 
at  a  very  early  period  of  childhood,  and  seems  capable  of  performing 
its  functions.  In  the  Human  species,  these  organs,  when  once  evolved, 
remain  always  in  a  state  of  preparation  for  the  performance  of  their 
function,  unless  they  are  atrophied  through  complete  disuse,  or  have 
lost  their  vigour  by  age,  or  through  excessive  demands  upon  their 
activity  ;  but  in  most  of  the  lower  animals,  the  development  of  these 
organs  is  periodical  through  the  whole  of  life,  taking  place  at  a  cer- 
tain season  of  the  year,  and  being  greatly  influenced,  it  would  ap- 
pear, by  the  external  temperature,  and  by  the  supply  of  food.  Thus 
in  the  Sparrow,  the  testes  are  no  larger  than  mustard-seeds,  during 
the  greatest  part  of  the  year;  but  in  the  spring,  they  acquire  the  size 
of  large  peas,  and  it  is  then  only  that  they  possess  any  procreative 
power. 

624.  We  are  not  always  to  judge  of  the  degree  of  development  of 
organs,  however,  by  their  size  alone ;  for  the  completeness  of  their 
structure,  and  their  aptitude  for  the  performance  of  their  functions, 
must  also  be  taken  into  the  account.  Thus  in  the  new-born  infant, 
the  organs  of  digestion  and  assimilation,  though  of  small  size,  are  so 
completely  formed,  as  to  be  able  at  once  to  take  on  the  duty  of  re- 
ceiving and  preparing  the  nutritive  materials,  provided  these  are  sup- 
plied in  a  form  adapted  to  their  powers;  the  circulating  apparatus  is 
fully  adequate  to  transmit  the  products  of  the  action  of  those  organs  to 
the  body  in  general,  and  to  bring  back  the  results  of  its  continual 
decay ;  and  the  respiratory  organs,  together  with  other  parts  of  the 
excretory  apparatus,  are  so  completely  evolved,  as  to  be  able  to  sepa- 
rate the  effete  matter,  and  cast  it  out  of  the  system,  with  an  energy 
equivalent  to  that  of  the  organs,  by  which  new  matter  is  introduced 
and  appropriated.  On  the  other  hand,  the  Brain,  although  of  larger 
comparative  size  at  birth,  than  at  any  subsequent  period  of  life,  is  but 
very  imperfectly  developed ;  for  its  structure  is  not  yet  so  far  com- 
pleted, as  to  prepare  it  for  a  state  of  high  functional  activity.  In  fact, 
it  would  seem  as  if  the  use  of  the  organ,  as  called  forth  by  the  new 
circumstances  in  which  the  infant  is  placed  as  soon  as  it  comes  into 
the  world,  is  essential  to  its  complete  development ;  and  the  same  may 
be  said  of  the  Muscular  system. 

625.  During  the  whole  period  of  infancy  and  childhood,  the  current 
of  nutrition  seems  peculiarly  directed  towards  the  brain  ;  for  though 
its  size  does  not  continue  to  increase  in  proportion  with  that  of  the 
remainder  of  the  body,  its  structure  is  evidently  being  rendered  more 


360  VARIATIONS  OF  NUTRITION  WITH  AGE. 

perfect,  and  its  functional  activity  is  excited  with  remarkable  facility. 
Hence  it  is  peculiarly  liable  to  be  acted  on  by  various  causes,  which 
may  produce  disease  ;  and  the  operation  of  remedies,  which  spe- ' 
cially  affect  that  organ,  is  far  more  powerful  than  at  any  other  period 
of  life.  Thus,  whilst  a  child  will  bear  a  fourth,  or  even  a  third,  of  the 
dose  of  a  purgative  adequate  for  an  adult,  it  is  strongly  affected  by  an 
eighth,  or  even  a  twelfth,  of  the  dose  of  a  narcotic  or  a  stimulant,  that 
would  be  required  to  produce  a  corresponding  effect  in  middle  life. 
This  peculiar  impressibility  of  the  nervous  system,  resulting  from  the 
activity  of  the  nutrient  processes  which  are  taking  place  in  it,  mani- 
fests itself  also  in  other  ways ;  thus  children  are  peculiarly  liable  to 
have  its  powers  depressed  by  any  sudden  shock,  such  as  a  blow,  or  an 
extensive  burn  or  laceration;  whilst,  on  the  other  hand,  if  the  depres- 
sion be  not  fatal,  they  recover  from  its  effects  much  more  speedily  than 
an  adult  would  do  from  a  similar  condition. 

626.  During  the  periods  of  youth  and  adolescence,  the  chief  energy 
of  development  (except  in  regard  to  the  generative  system,  already 
noticed),  appears  to  be  directed  towards  the  Muscular  apparatus; 
which  then  increases  in  vigour,  in  a  degree  which  surpasses  its 
increase  of  size ;  and  the  circulating  and  respiratory  organs,  upon 
whose  energetic  action  there  is  then  a  corresponding  demand,  are 
peculiarly  liable  to  disturbance  of  function,  inducing  disease  in  them- 
selves or  in  other  parts.  The  maladies  of  this  period  are  for  the  most 
part  of  a  sthenic  or  inflammatory  character ;  resulting,  as  we  shall 
presently  see,  from  the  excessive  activity  of  the  assimilating  pro- 
cesses, which  are  disposed  to  produce  more  fibrin  than  the  wants  of 
the  body  require.  Or  if,  on  the  other  hand,  there  be  an  imperfect 
elaboration  of  the  nutrient  materials,  as  happens  in  the  tubercular 
diathesis,  its  effects  are  peculiarly  liable  to  manifest  themselves  at 
this  period,  when  the  demand  for  nutritive  matter  is  greatly  aug- 
mented by  the  activity  of  the  muscular  system. 

627.  In  adult  age,  there  should  be  such  a  balance  of  all  the  func- 
tions, arising  from  the  due  development  and  proper  use  of  each  organ, 
as  may  preserve  the  body  in  the  state  of  health  and  vigour,  without 
any  marked  change  in  the  relative  dimensions  of  its  different  parts, 
through  a  long  series  of  years.  The  digestive,  assimilating,  and 
excreting  organs,  as  they  were  the  first  to  come  to  maturity,  are  com- 
monly the  first  to  fail  in  their  activity;  but  this  is  very  generally  the 
result  of  over-exertion  of  their  powers,  the  amount  of  food  introduced 
into  the  stomach  being  rarely  (among  the  higher  and  middle  classes 
of  society  at  least)  kept  down  to  the  real  wants  of  the  system.  The 
muscular  apparatus  usually  experiences  the  effects  of  this  diminished 
nutrition  sooner  than  the  nervous  system ;  the  vigour  of  the  latter 
being  often  sustained  in  a  remarkable  degree  (as  shown  by  the  energy 
of  the  mental  operations)  through  a  protracted  life,  when  it  has  not 
been  over-tasked  at  an  earlier  period.  The  very  slight  impairment 
of  the  nutrition  of  the  nervous  system,  during  the  general  emaciation 
which  results  from  a  wasting  disease,  or  during  that  more  gradual 


VARIOUS  CAUSES  OF  DEATH.  361 

decline  of  the  bodily  vigour  which  is  consequent  upon  advancing 
age,  is  a  phenomenon  which  strongly  marks  it  out  as  the  part  of  the 
body,  to  the  maintenance  of  whose  integrity  everything  else  is  sub- 
servient; and  this  is  still  more  remarkably  shown  in  the  phenomena 
of  starvation  ;  in  which,  notwithstanding  the  disappearance  of  the 
whole  of  the  fat,  and  the  reduction  of  the  weight  of  the  body  in  general 
by  about  40  per  cent.,  the  nervous  system  appears  to  lose  little  or  none 
of  its  substance  (§  117). 

3.  Of  Death ,  or  Cessation  of  JVutrition. 

628.  The  general  cessation  of  the  Nutritive  operations^  in  Death, 
usually  depends,  as  formerly  explained  (§  65),  upon  the  cessation  of 
the  supply  of  Nutriment,  in  consequence  of  the  stagnation  of  the  Cir- 
culating current ;  and  this  stagnation  may  result  from  the  direct  ope- 
ration of  three  causes ;  namely, — failure  in  the  propulsive  power  of 
the  Heart,  or  Syncope, — obstruction  to  the  flow  of  blood  through  the 
pulmonary  capillaries,  consequent  upon  a  deficient  supply  of  air,  or 
Asphyxia, — and  a  disordered  state  of  the  blood  itself  (§  534),  which 
at  the  same  time  weakens  the  power  of  the  heart,  and  prevents  the 
performance  of  those  changes  in  the  systemic  capillaries,  which  afford 
a  powerful  auxiliary  to  the  circulation ;  a  mode  of  death,  for  which 
the  term  JVecrcemia  has  been  proposed.  Each  of  these  conditions  may 
be  dependent  upon  a  variety  of  remote  causes,  which  need  not  here 
be  particularized.  But  it  is  evident  that,  when  either  one  of  them 
has  been  established,  the  nutritive  processes  must  speedily  cease, 
although  they  may  continue  for  a  short  time  at  the  expense  of  the 
blood  in  the  capillaries  of  the  part.  The  cooling  of  the  body  is 
another  cause  of  their  cessation ;  and  this  is  one  reason  why  molecular 
death  (or  the  death  of  the  individual  organs  and  tissues)  follows  so 
much  more  closely  on  somatic  death  (or  the  cessation  of  the  circula- 
ting and  respiratory  functions),  in  warm-blooded  than  in  cold-blooded 
animals.  In  either  case,  however,  the  solid  tissues  may  preserve  for 
a  time  their  independent  vitality ;  and  changes  may  take  place  in 
them,  which  indicate  the  continuance  of  their  nutritive  actions  to  a 
certain  extent,  even  when  they  have  been  disconnected  from  the  body. 

629.  Although  the  death  of  the  several  parts  composing  the  fabric 
is  thus  due,  in  the  great  majority  of  cases,  to  the  supensions  of  the 
supply  of  the  nutritive  materials,  and  to  the  lowering  of  the  tempera- 
ture of  the  body,  yet  there  are  undoubtedly  cases,  in  which  the  loss 
of  vital  power  is  as  complete  in  the  solids  as  in  the  fluids ;  the  want 
of  ability  to  avail  themselves  of  nutriment,  being  as  decided  in  the 
former,  as  the  deficiency  of  supply  is  in  the  latter.  This  is  seen,  for 
example,  when  death  results  from  a  sudden  and  violent  shock,  which 
destroys  the  vitality  of  the  whole  system  alike  (§  604).  But  it  can 
scarcely  be  doubted,  that  we  are  to  attribute  the  gradual  decay  and 
death,  which  take  place  in  extreme  old  age  without  any  symptom  of 
local  disease,  to  a  similar  cause.     We  have  seen  that  every  individual 


362  NATURAL  DEATH.— INFLAMMATION. 

part  of  the  fabric  has  its  own  allotted  period  of  life  and  activity  ;  each 
cell  passing  through  a  certain  series  of  changes,  which  are  proper  to 
it,  and  then  ceasing  to  exist ;  and  many  organs  having  only  a  limited 
period  of  activity,  and  disappearing  more  or  less  completely,  when 
this  has  been  accomplished.  In  both  cases,  the  usual  duration  of  the 
organ  is  usually  diminished  by  any  previous  excess  of  activity,  and 
increased  by  moderation  in  the  exercise  of  its  vigour.  Thus,  the  life 
of  the  individual  cells  of  the  simple  cellular  plants  (on  which  our 
observations  as  to  some  of  the  conditions  of  cell-growth  may  be  best 
made),  is  shortened  by  such  external  influences  as  are  most  favourable 
to  rapidity  in  their  growth  and  development.  And  in  Man,  we  con- 
stantly notice  that  the  duration  of  the  powers  of  the  Brain  and  the 
Generative  system  is  the  longest,  when  these  organs  have  been  mode- 
rately exercised  ;  and  that  it  is  much  curtailed  by  the  excessive  use  of 
either.  The  duration  of  their  activity,  however,  is  not  increased  by 
partial  or  entire  disuse  of  the  organs ;  for  this  induces  a  state  of 
atrophy,  on  the  principles  already  mentioned.  Now  we  have  every 
reason  to  believe,  that  what  is  true  of  individual  parts  and  organs,  is 
true  also  of  the  whole  structure  ;  and  that  the  existence  of  the  entire 
bodily  fabric  may  thus  come  to  an  end,  without  any  special  disease, 
in  consequence  of  the  limit  originally  set  to  its  powers  of  self-renova- 
tion. It  is  but  rarely,  however,  that  this  occurs ;  the  various  acci- 
dents of  life,  the  neglect  of  ordinary  precautions  for  the  preservation 
of  health,  and  hereditary  tendencies  to  various  kinds  of  morbid  action, 
being  too  frequently  the  means  of  cutting  off'  the  term  of  Human 
existence,  long  before  its  natural  expiration. 

4.  Disordered  Conditions  of  the  JVutritive  Processes. 

630.  Having  thus  passed  in  review  the  general  conditions,  under 
which  the  ordinary  Nutritive  processes  take  place,  it  may  be  well  to 
add  a  few  w^ords  in  relation  to  two  of  their  abnormal  states ;  one  or 
other  of  which  is  concerned  in  a  very  large  proportion  of  the  diseases 
that  afflict  the  human  race.  In  one  of  these,  there  is  a  tendency  to 
the  excessive  production  of  Fibrin  in  the  blood ;  whilst  in  the  other, 
there  is  a  want  of  the  proper  nutritive  power  in  the  tissues,  which  is 
apparently  due  to  an  imperfect  elaboration  of  that  important  material. 
The  one  of  these  conditions  is  termed  Inflammation;  whilst  the  other, 
which  is  less  active,  but  more  insidious,  is  known  as  the  Tubercular 
Diathesis. 

631.  The  extraordinary  tendency  to  the  production  of  Fibrin  in 
the  blood,  which  has  been  already  noticed  (§  531)  as  the  most  import- 
ant character  of  Inflammation,  seems  to  be  always  conjoined  with  a 
depressed  vitality  of  the  tissues  of  some  part  of  the  body,  which  indis- 
poses them  to  the  performance  of  their  regular  nutritive  operations  ; 
and  this  part  may  undergo  a  variety  of  changes,  according  to  the 
degree  in  which  it  is  affected.  The  depressed  condition  of  its  nutri- 
tive operations  involves,  on  the  principles  explained  in  the  preceding 


INFLAMMATION  5    SUPPURATION;    GANGRENE.  363 

chapter,  a  languor  in  the  movement  of  blood  through  it,  together  with 
a  distensible  state  of  the  capillaries,  which  causes  them  to  contain  a 
far  greater  amount  of  that  fluid  than  under  ordinary  circumstances. 
There  appears  to  be,  in  the  vessels  of  an  inflamed  part,  a  peculiar 
attraction  for  the  white  corpuscles  of  the  blood,  by  which  they  are 
drawn  together  from  the  circulating  current ;  and  there  is  also  a  tend- 
ency to  an  increased  production  of  them,  which  is  probably  the  cause 
of  the  increase  in  the  total  amount  of  fibrin.  This  increase  of  fibrin 
in  the  blood,  coupled  with  a  diminished  power  of  appropriating  it  on 
the  part  of  the  tissues,  appears  to  constitute  the  essential  phenomena 
of  the  Inflammatory  condition,  and  to  be  the  cause  of  the  other  changes 
which  are  characteristic  of  it. 

632.  The  simplest  result  of  this  condition,  is  the  effusion  of  fibri- 
nous matter,  or  organizable  lymph,  into  the  substance  of  the  part 
inflamed,  or  upon  the  nearest  free  surface;  and  thus  is  produced  a 
condensation  of  the  tissue,  or  a  new  growth  upon  the  membrane. 
But  when  the  depression  of  vitality  is  more  complete,  the  tissue  at 
that  spot  gradually  dies  and  disintegrates  ;  and  whilst  itself  undergo- 
ing such  changes,  it  gives  origin  to  similar  changes  in  the  eff*used 
fibrin,  which  it  converts  from  ?i  plastic  or  organizable  deposit,  into  an 
aplastic  or  unorganizable  one,  namely,  pus.  Thus  is  produced  the 
Suppurating  process  ;  which  may  either  take  place  in  a  cavity  thus 
excavated  in  the  substance  of  a  tissue  or  organ  ;  or  on  a  free  surface. 
In  either  case,  the  surrounding  tissues,  which  are  less  inflamed,  and 
in  which  the  vitality  is  impaired  but  not  destroyed,  become  consoli- 
dated by  a  deposition  of  organizable  fibrin,  which  prevents  the  infil- 
tration of  pus  through  their  substance.  If  this  should  not  occur, 
through  a  want  of  power  to  generate  well-elaborated  fibrin,  the  sup- 
purating process  extends  itself  rapidly,  with  the  most  calamitous 
results;  the  properties  of  pus  being  such  as  to  produce  a  tendency 
to  decomposition,  both  in  the  blood  and  in  the  solid  tissues  into  the 
substance  of  which  it  may  be  carried. 

633.  The  process  termed  Gangrene^  which  is  the  entire  loss  of  vi- 
tality in  the  part,  with  a  complete  cessation  of  the  circulation  through 
it,  is  commonly  ranked  as  one  of  the  results  of  Inflammation ;  but  it 
can  hardly,  in  strictness,  be  so  regarded.  We  have  a  well-marked 
illustration  of  the  mode  in  which  this  local  death  takes  place,  in  the 
case  of  frost-bites  produced  by  Cold ;  for  this  agent  at  the  same  time 
produces  contraction  of  the  blood-vessels,  and  depression  of  the  vital 
powers  of  the  solid  tissues,  proceeding  to  the  complete  destruction  of 
them;  whilst  in  the  parts  adjoining  those  which  are  actually  killed, 
the  inflammatory  state  is  developed  ;  producing  an  effusion  of  fibrin, 
which  serves  to  plug  up  the  mouths  of  the  vessels,  and  thus  to  prevent 
hemorrhage,  when  the  mortified  part  drops  off*.  Here  we  see,  that 
the  violent  action  of  cold  completely  destroys  the  vitality  of  the  part 
most  exposed  to  it;  and  this  by  its  direct  influence  on  the  properties 
of  the  organized  structure.  No  inflammation  can  take  place  in  the 
part  thus  killed,  because  the  vital  processes  are  altogether  brought  to 


364     GANGRENE;  ULCERATION.— REPARATIVE  PROCESS. 

an  end.  But  inflammation  takes  place  in  the  adjoining  parts,  which 
are  less  seriously  affected  ;  for  the  depression  of  their  vital  powers 
occasions  the  result  already  adverted  to, — namely,  the  production  of 
an  increased  amount  of  Fibrin  in  the  blood,  and  an  infiltration  of 
this  substance  into  their  tissues.  The  same  is  the  case  with  regard 
to  the  operation  of  other  powerful  agents  ;  such  as  those  which  (like 
Caustic  potass,  or  Sulphuric  Acid)  destroy  the  vitality  of  the  parts  to 
which  they  are  applied,  by  the  chemical  decomposition  of  their  tis- 
sues. The  Inflammatory  process  is  set  up,  not  in  the  parts  which  are 
killed  by  the  application ;  but  in  the  surrounding  tissues,  whose 
vitality  has  been  simply  depressed ;  and  thus,  when  the  slough,  or 
dead  part,  is  cast  off*,  there  is  a  preparation  for  the  development  of 
new  tissue  to  supply  its  place,  from  the  superabundant  plastic  mate- 
rials of  the  surrounding  parts. 

634.  If,  then,  we  limit  the  term  Inflammation,  as  there  seems 
reason  to  do,  to  that  state,  in  which  there  is  a  tendency  to  stagnated 
circulation,  with  increased  production  of  Fibrin,  in  the  vessels  of  the 
part,  we  see  that  Gangrene  cannot  be  a  result  of  that  process,  which 
is  one  rather  of  reparation  than  of  destruction.  But  Gangrene  pro- 
ceeds, where  we  can  distinctly  trace  its  causes,  from  the  violent  ope- 
ration of  the  same  agents,  as  those  which,  in  a  less  degree,  produce 
Inflammation.  And  where  this  last  process  is  not  set  up,  at  the  line 
of  demarkation  between  the  living  and  the  dead  parts,  Gangrene,  like 
Suppuration,  has  a  tendency  to  spread  ;  the  influence  of  the  decay, 
which  is  taking  place  in  one  part,  having  a  tendency  to  propagate 
itself  to  the  adjoining  tissues ;  and  a  constantly  extending  destruction 
being  thus  produced. 

635.  In  like  manner,  certain  forms  of  the  Ulcerating  process  may 
spread,  by  the  action  of  a  peculiat  layer  of  cells,  that  is  found  on  the 
surface  of  the  excavation ;  these  cells  appear  to  possess  the  power  of 
drawing  into  themselves  the  materials  of  the  solid  tissues  on  which 
they  lie,  and  thus  of  causing  their  destruction;  and  this  destructive 
action  may  take  place  to  an  unlimited  degree,  if  no  measures  betaken 
to  check  it.  The  application  of  powerful  escharotics  (such  as  nitric 
acid,  lunar  caustic,  or  the  actual  cautery),  which  is  w^ell  known  to  be 
one  of  the  most  efficient  methods  of  treatment  in  this  kind  of  diseased 
action,  has  the  effect  of  destroying  these  peculiar  cells,  together  with 
the  adjacent  tissue  which  has  been  partly  affected  by  them;  and  of 
exciting  an  inflammatory  action  beneath,  by  which  fibrin  may  be 
effused,  and  preparation  made  for  filling  up  the  breach  of  substance. 

636.  Now  when  the  reparation  of  lost  parts  takes  place,  it  may  be 
effected  in  either  of  two  modes ; — by  a  process  of  growth  analogous 
to  the  natural  one ; — or  by  the  formation  of  a  new  kind  of  tissue, 
termed  granulation-structure,  from  the  surface  of  which  a  formation 
of  pus  takes  place,  until  the  cavity  is  completely  filled  up  by  it,  and 
closed  over  by  skin,  after  which  the  granulation-structure  is  absorbed, 
and  a  contracted  cicatrice  is  left.  The  former  mode  of  reparation, 
which  takes  place  in  cold-blooded  animals,  is  the  slowest,  but  it  is 


REPARATIVE  PROCESSES.—TUBERCULAR  DIATHESIS.  365 

the  most  complete  ;  for  as  the  breach  of  substance  is  filled  up  by 
tissue  of  a  permanent  kind,  there  is  no  subsequent  contraction  nor 
cicatrix ;  nor  is  there  that  waste  of  plastic  matter,  nor  that  constitu- 
tional irritation,  which  is  attendant  on  the  suppurating  process.  It 
is,  consequently,  that  which  the  Surgeon  should  aim  to  produce  ;  and 
the  means  of  accomplishing  this  consists  in  keeping  down  the  Inflam- 
matory process,  and  in  preventing  irritation  of  the  exposed  surface. 

637.  In  all  cases  of  injury,  there  is  an  increased  determination  of 
blood  to  the  neighbouring  tissues;  and  an  increased  production  of 
Fibrin,  to  serve  as  the  material  for  repair.  Now  if  this  be  moderate 
in  its  amount  (as  it  usually  is  in  cold-blooded  animals),  it  will  be  all 
consumed  in  the  formation  of  the  new  tissue,  which  is  to  fill  up  the 
vacuity.  But  if  it  be  excessive,  it  forms  an  inflammatory  eflTusion  ; 
part  of  which  undergoes  a  low  degree  of  organization,  and  becomes 
granulation-structure  ;  whilst  another  part  is  poured  forth  from  the 
copious  but  imperfectly-formed  vessels  of  that  structure,  in  an  unor- 
ganizable  state,  forming  Pus.  This  change  in  its  character  is  mainly 
due  to  the  irritating  influence  of  cold  air;  which  also  tends  to  keep 
up  the  excessive  production  of  Fibrin  by  the  Inflammatory  process; 
and  the  more  carefully  the  raw  surface  is  kept  from  contact  with  it, 
the  more  healthy  will  be  its  action.  The  low  temperature  of  cold- 
blooded animals  prevents  the  air  from  having  a  like  injurious  eflfect 
upon  their  wounded  surfaces  ;  no  exclusion  of  it  seems  necessary.  In 
warm-blooded  animals  the  desired  end  may  be  attained,  either  by  the 
application  of  hot  dry  air,  which  causes  a  scab  to  form,  beneath  which 
the  reparative  process  may  take  place  in  complete  seclusion  from 
external  irritation ;  or  by  the  formation  of  an  artificial  covering, 
equally  closely  applied,  by  means  of  a  waxy  or  resinous  ointment, 
spread  in  a  liquid  state  (a  measure  which  has  proved  peculiarly  effi- 
cacious in  the  treatment  of  burns) ;  or  by  the  application  of  steam  to 
the  wounded  surface,  w^hich  seems  to  have  a  remarkably  soothing 
effect  upon  it ;  or,  where  there  is  a  tendency  to  violent  inflammation 
(as  in  wounds  of  the  large  joints),  by  keeping  the  dressings  moist  by 
a  continual  supply  of  cool  (but  not  cold)  water.  All  these  modes  of 
treatment  act  in  the  same  manner ;  tending  to  exclude  irritation,  to 
keep  down  inflammation,  to  prevent  the  over-production  of  fibrin, 
and  to  promote  the  natural  process  of  slow  reparative  growth. 

638.  If  the  Fibrin  of  the  Blood,  however,  be  not  well  elaborated, 
it  does  not  possess  its  due  organizability ;  and  thus,  instead  of  being 
converted  by  the  Nutritive  process  into  solid  tissue,  proper  to  the  part 
in  which  it  is  deposited,  it  is  liberated  from  the  vessels  in  a  state, 
which  prevents  any  but  a  very  imperfect  structure  from  being  deve- 
loped by  it.  This  is  the  condition  of  the  Tubercular  substance,  which 
is  so  often  found  to  replace  the  proper  tissue,  especially  in  the  lungs ; 
being  slowly  deposited  there,  by  a  sort  of  degradation  of  the  regular 
nutritive  operations ;  and  being  effused  in  larger  quantity,  when  the 
inflammatory  process  is  set  up.  There  is  every  degree  of  gradation 
between  the  plastic  or  organizable  deposit  of  well-elaborated  Fibrin, 


366  TUBERCULAR  DIATHESIS.— MALIGNANT  GROWTHS. 

the  caco'plastic  or  imperfecily-organizahle  matter  of  Tubercle,  and  the 
aplastic  or  non-organizable  matter  of  Pus.  The  Microscopic  exami- 
nation of  tubercular  deposit  shows,  that  they  sometimes  contain  fully 
developed  cells  and  fibres,  analogous  to  those  of  fibrinous  exudations  ; 
but  that  more  frequently,  the  cells  and  fibres  are  imperfectly  formed, 
and  are  accompanied  by  a-  large  quantity  of  a  granular  substance, 
which  strongly  resembles  coagulated  Albumen ;  and  that  in  many 
cases,  there  is  scarcely  any  trace  of  organization  in  the  mass.  The 
greatest  degree  of  organization  is  found  in  the  semi-transparent,  mili- 
ary, gray,  and  tough  yellow  forms  of  Tubercle  ;  the  least  in  the  opaque, 
crude,  or  yellow  Tubercle. 

639.  The  constitutional  state,  w-hich  predisposes  to  this  perversion 
of  the  ordinary  nutritive  operations,  and  which  is  known  as  the  Tu- 
bercular Diathesis,  is  the  result  of  the  continued  operation  of  any 
causes,  that  tend  to  depress  the  vital  powers ;  such  as  insuflScient 
nutrition,  habitual  exposure  to  cold  and  damp,  protracted  mental 
depression,  &c. ;  or  it  may  be  derived  from  the  operation  of  the  same 
or  other  causes  on  the  ancestors  of  the  individual,  being  one  of  those 
disorders  which  has  a  peculiar  tendency  to  become  hereditary.  The 
treatment  must  be  directed  to  the  invigoration  of  the  system  by  good 
food,  active  exercise,  pure  air,  warm  clothing,  and  cheerful  occupa- 
tions ;  and  by  the  due  employment  of  those  means,  at  a  sufficiently 
early  period,  many  valuable  lives  may  be  saved,  which  would  other- 
wise fall  a  sacrifice  to  Tubercular  disease  in  the  lungs,  or  other  import- 
ant organs. 

640.  There  is  another  remarkable  class  of  diseases,  resulting  from 
a  disordered  condition  of  the  nutritive  processes ; — those,  namely,  of 
a  malignant  nature.  We  not  unfrequently  meet  with  abnormal  growths 
of  a  fatty,  cartilaginous,  fibrous,  or  bony  structure ;  which  appear  to 
originate  in  some  perverted  action  of  the  part  itself,  and  which  have 
little  tendency  to  reappear  in  the  same  part,  w^hen  they  have  been 
removed, — still  less,  to  reappear  in  distant  parts.  But  the  various 
forms  of  Malignant  or  Cancerous  disease  are  peculiar  in  this, — that 
they  are  composed  of  cells,  sometimes  of  a  globular  form,  (see  Fig. 
30),  sometimes  elongated  or  spindle-shaped,  having  a  power  of  rapid 
multiplication,  and  not  capable  of  changing  into  any  other  kind  of 
tissue.  When  a  truly  cancerous  growth  has  once  established  itself  in 
any  part  of  the  body,  it  may  increase  to  an  unlimited  extent,  obtain- 
ing its  nourishment  from  the  blood-vessels  in  its  neighbourhood,  and 
destroying  the  surrounding  parts  by  its  pressure,  as  well  as  by  draw- 
ing off  their  supply  of  aliment.  When  it  has  developed  itself  to  a 
considerable  degree  in  one  part,  it  is  very  liable  to  make  its  appear- 
ance in  others;  probably  in  consequence  of  the  germs  of  the  cells 
being  conveyed  in  the  circulating  current  to  distant  portions  of  the 
body:  and  hence  the  judicious  surgeon  is  disinclined  to  remove  a 
Cancerous  growth  of  any  but  the  most  limited  kind;  knowing  that 
the  disease  is  almost  certain  to  reappear.  There  is  a  strong  analogy 
betw^een  such  Cancerous  growths,  and  the  low  forms  of  Fungoid 


NEED  OF  RESPIRATION  IN  ANIMALS.  367 

Vegetation,  which  develop  themselves  in  the  interior  of  the  higher 
Plants,  and  even  in  Animal  bodies  ;  and  in  both  cases,  the  disease 
may  be  propagated  by  inoculation  from  one  individual  to  another,  the 
transplantation  of  a  few  cell-germs  being  all  that  is  required. 


CHAPTER  VIII. 

OF  RESPIRATION. 

1 .  Essential  Mature  and  Conditions  of  the  Respiratory  Process. 

641.  The  function  of  Respiration  essentially  consists  of  an  inter- 
change of  oxygen  and  carbonic  acid  between  the  blood  of  the  Animal 
and  the  surrounding  medium  ;  carbonic  acid  being  given  out  by  the 
blood,  and  oxygen  entering  in  its  stead.  .  It  has  been  already  noticed 
(§  84)  that  this  function  is  performed  likewise  by  Plants;  although, 
in  consequence  of  their  deriving  a  large  part  of  their  food  from  the 
atmosphere  by  a  converse  process — the  absorption  of  carbon  and  the 
liberation  of  oxygen, — their  true  respiration  is  commonly  overlooked. 
It  may,  therefore,  be  regarded  as  common  to  all  Organized  beings. 
Every  one  is  conscious,  in  his  own  person,  of  the  imperative  demand 
for  the  due  performance  of  this  operation.  If  the  breath  be  purposely 
held  for  even  a  few  seconds,  a  feeling  of  distress  is  experienced, 
which  increases  every  moment,  and  at  last  prompts  irresistibly  to  the 
respiratory  movement.  And  if  the  admission  of  air  to  the  lungs  be  in 
any  way  prevented,  the  respiratory  movements  are  at  first  increased 
in  energy,  violent  efforts  are  made  to  obtain  the  needed  supply;  these 
are  succeeded  by  irregular  convulsive  actions,  and  at  the  same  time 
insensibility  comes  on ;  and  within  a  short  time  all  movement  ceases, 
the  circulation  of  the  blood  is  suspended,  and  a  stop  is  put  to  all  the 
vital  operations  of  the  body.  This  state,  which  is  termed  Asphyxia, 
usually  comes  on,  in  a  warm-blooded  animal,  within  ten  minutes  of 
the  time  when  the  respiration  is  completely  suspended ;  thus  affording 
the  most  convincing  proof  of  the  importance  of  that  function  in  the 
Animal  economy.  In  many  cold-blooded  tribes,  a  much  longer  sus- 
pension may  be  borne  with  impunity;  as  also  by  warm-blooded  ani- 
mals, when  the  general  activity  of  their  functions  is  lowered  in  the 
state  of  hybernation  (§  121).  We  shall  now  inquire  into  the  sources 
of  the  necessity  for  this  interchange  of  oxygen  and  carbonic  acid ; 
and  the  mode  in  which  the  suspension  of  it  acts  upon  the  system  at 
large. 

642.  All  Organized  bodies,  as  already  explained,  are  liable  to  con- 
tinual decay,  even  whilst  they  are  most  actively  engaged  in  perform- 
ing the  actions  of  Life ;  and  one  of  the  chief  products  of  that  decay  is 


368        SOURCES  OF  EXCRETION  OP  CARBONIC  ACID. 

carbonic  acid.  A  large  quantity  of  this  gas  is  set  free,  during  the 
decomposition  of  almost  every  kind  of  organized  matter ;  the  carbon 
of  the  substance  being  united  with  oxygen  supplied  by  the  air.  Hence 
we  find,  that  the  formation  and  liberation  of  carbonic  acid  go  on  with 
great  rapidity  after  death,  both  in  the  Plant  and  in  the  Animal ;  and 
that  they  take  place  also,  to  a  very  great  extent,  in  the  period  that 
often  precedes  the  death  of  the  body,  during  which  a  general  decom- 
position of  the  tissues  is  taking  place.  Thus  in  Plants,  as  soon  as 
they  become  unhealthy,  the  extrication  of  carbon  in  the  form  of  car- 
bonic acid  takes  place  in  greater  amount  than  its  fixation  from  the 
carbonic  acid  of  the  atmosphere ;  and  the  same  change  normally  takes 
place  during  the  period  that  immediately  precedes  the  annual  fall  of 
the  leaves,  their  tissue  being  no  longer  able  to  perform  its  proper 
functions,  and  giving  rise,  by  its  incipient  decay,  to  a  large  increase 
in  the  quantity  of  carbonic  acid  set  free.  The  same  thing  happens 
in  the  Animal  body,  during  the  progress  of  many  diseases  which  are 
attended  with  an  unusual  tendency  to  decomposition  in  the  solids  and 
fluids, — such  as  eruptive  fevers : — the  quantity  of  carbonic  acid  set 
free  in  Respiration  is  greatly  increased,  although  the  body  remains 
completely  at  rest ;  and  notwithstanding  this,  the  blood  frequently  ex- 
hibits an  unusually  dark  hue,  indicating  that  it  has  not  been  properly 
freed  from  the  unusual  amount  of  that  substance,  which  it  has  received 
from  the  tissues. 

643.  Hence,  the  first  object  of  the  Respiratory  process,  which  is 
common  to  all  forms  of  Organized  being,  is  to  extricate  from  the  body 
the  carbonic  acid,  which  is  one  of  the  products  of  the  continual  decom- 
position of  its  tissues.  The  softness  of  many  of  the  tissues  of  Animals, 
and  the  large  quantity  of  fluid  contained  in  their  bodies,  render  them 
more  prone  than  plants  to  this  kind  of  decomposition ;  and,  in  warm- 
blooded animals,  the  higher  temperature  at  which  the  fabric  is  usually 
maintained,  adds  considerably  to  the  degree  of  this  tendency;  so  that 
the  waste  of  their  tissues,  from  this  cause  alone,  is  as  much  greater 
than  that  of  cold-blooded  animals  as  the  latter  is  than  that  of  Plants. 
But  when  the  temperature  of  the  Reptile  is  raised  by  external  heat  to 
the  level  of  that  of  the  Mammal,  its  need  for  respiration  increases, 
owing  to  the  augmented  waste  of  its  tissues.  When,  on  the  other 
hand,  the  warm-blooded  Mammal  is  reduced,  in  the  state  of  hyberna- 
tion, to  the  level  of  the  cold-blooded  Reptile,  the  waste  of  its  tissues 
diminishes  to  such  an  extent,  as  to  require  but  a  very  small  exertion  of 
the  respiratory  process  to  get  rid  of  the  carbonic  acid,  which  is  one  of 
its  chief  products.  And  in  those  animals  which  are  capable  of  retain- 
ing their  vitality  when  frozen  (§  136),  or  when  their  tissues  are  com- 
pletely dried  up  (§  159),  the  decomposition  is,  for  the  time,  entirely 
suspended,  and  consequently  there  is  no  carbonic  acid  to  be  set  free. 

644.  But  another  source  of  Carbonic  acid  to  be  set  free  by  the  Re- 
spiratory process,  and  one  which  is  peculiar  to  Animals,  consists  in  the 
rapid  changes  which  take  place  in  the  Muscular  and  Nervous  tissues, 
during  the  period  of  their  activity.    It  has  been  already  shown  (§  361), 


SOURCES  OF  EXCRETION  OF  CARBONIC  ACID.  369 

that  there  is  strong  reason  to  believe  the  waste  or  decomposition  of 
the  Muscular  tissue  to  be  in  exact  proportion  to  the  degree  in  which  it 
is  exerted ;  every  development  of  muscular  force  being  accompanied 
by  a  change  in  the  condition  of  a  certain  amount  of  tissue.  In  order 
that  this  change  may  take  place,  the  presence  of  Oxygen  is  essential ; 
and  one  of  the  products  of  the  union  of  oxygen  with  the  elements  of 
muscular  fibre  is  carbonic  acid.  The  same  may  probably  be  said  of 
the  Nervous  tissue  (§  384).  Hence  it  may  be  stated  as  a  general 
principle,  that  the  peculiar  waste  of  the  Muscular  and  Nervous  sub- 
stances, which  is  a  condition  of  their  functional  activity,  and  which  is 
altogether  distinct  from  the  general  slow  decay  that  is  common  to  these 
tissues  with  others,  is  another  source  of  the  carbonic  acid  which  is  set 
free  from  the  animal  body ;  and  that  the  amount  thus  generated  will 
consequently  depend  upon  the  degree  in  which  these  tissues  are  exer- 
cised. In  animals  which  are  chiefly  made  up  of  the  organs  of  vege- 
tative life,  in  whose  bodies  the  nervous  and  muscular  tissues  form  but 
a  very  small  part,  and  in  whose  tranquil  plant-like  existence  there  is 
but  very  little  demand  upon  the  exercise  of  these  structures,  the  quan- 
tity of  carbonic  acid  thus  liberated  will  be  extremely  small.  On  the 
other  hand,  in  animals  whose  bodies  are  chiefly  composed  of  muscle, 
and  whose  life  is  an  almost  ceaseless  round  of  exertion,  the  quantity 
of  carbonic  acid  thus  liberated  is  very  considerable. 

645.  We  are  enabled  to  trace  the  connection  between  the  amount 
of  muscular  exertion,  and  the  quantity  of  carbonic  acid  set  free  in  the 
act  of  respiration,  in  the  class  of  Insects,  better  than  in  any  other. 
They  have  no  fi3j:ed  temperature  to  maintain:  and  they  are,  conse- 
quently, not  in  the  condition  of  warm-blooded  animals,  in  which  the 
quantity  of  carbonic  acid  set  free  is  kept  up  to  a  more  regular  standard 
by  the  provision  to  be  presently  noticed.  On  the  other  hand,  they  are 
pre-eminent  among  all  Animals,  in  regard  to  the  energy  of  their  mus- 
cular power  in  relation  to  the  bulk  of  their  bodies;  and  the  waste  of 
muscular  tissue  during  their  state  of  activity  must  therefore  be  very 
great.  Thus,  a  Humble  Bee  has  been  found  to  produce  one-third  of  a 
cubic  inch  of  carbonic  acid  in  the  course  of  a  single  hour,  during  which 
its  whole  body  was  in  a  state  of  constant  movement,  from  the  ex- 
citement consequent  upon  its  capture ;  and  yet  during  the  whole 
twenty-four  hours  of  the  succeeding  day,  which  it  passed  in  a  state  of 
comparative  rest,  the  quantity  of  carbonic  acid  generated  by  it  was 
absolutely  less. 

646.  Besides  these  sources  of  Carbonic  acid,  which  are  common  to 
all  Animals,  there  is  another,  which  appears  to  be  peculiar  to  the  two 
highest  classes,  Birds  and  Mammals.  These  are  capable  of  maintain- 
ing a  constantly  elevated  temperature,  as  long  as  they  are  supplied 
with  a  proper  amount  of  appropriate  food  ;  and  their  power  of  doing 
so  appears  to  depend  upon  the  direct  combination  of  certain  elements 
of  the  food,  with  the  oxygen  of  the  air,  by  a  process  analogous  to  com- 
bustion ;  these  elements  having  been  introduced  into  the  blood  for  that 
purpose,  but  not  having  formed  a  part  of  any  of  the  solid  tissues  of  the 

24 


370        SOURCES  OF  EXCRETION  OF  CARBONIC  ACID. 

body,  unless  they  have  been  deposited  in  the  form  of  fat.  The  nature 
of  these  substances  has  been  already  noticed  (§  430).  It  is  quite 
clear  that  they  cannot  be  applied  in  their  original  form,  to  the  nutri- 
tion of  the  tissues  that  originate  in  proteine-compounds;  and  it  is  tole- 
rably certain  that  in  the  ordinary  condition  of  the  body,  they  undergo 
no  such  conversion  as  would  adapt  them  to  that  purpose.  The  Liver 
seems  to  afford  a  channel,  by  which  some  of  the  fatty  matters  are 
drawn  off  from  the  blood;  but  even  these  seem,  in  part  at  least,  to  be 
re-absorbed  (§  725),  and  to  be  thrown  off  by  the  respiratory  process. 

647.  The  quantity  of  carbonic  acid  that  is  generated  directly  from 
the  elements  of  the  food,  seems  to  vary  considerably  in  different  ani- 
mals, and  in  different  states  of  the  same  individual.  In  the  Carnivo- 
rous tribes,  which  spend  the  greater  part  of  their  time  in  a  state  of 
activity,  it  is  probable  that  the  quantity  which  is  generated  by  the 
waste  or  metamorphosis  of  the  tissues  is  sufficient  for  the  maintenance 
of  the  required  temperature, — and  that  little  or  none  of  the  carbonic 
acid  set  free  in  respiration  is  derived  from  the  direct  combustion  of 
the  materials  of  the  food.  But  in  Herbivorous  animals  of  compara- 
tively inert  habits,  the  amount  of  metamorphosis  of  the  tissues  is  far 
from  being  sufficient;  and  a  large  part  of  the  food,  consisting  as  it 
does  of  substances  that  cannot  be  applied  to  the  nutrition  of  the  tis- 
sues, is  made  to  enter  into  direct  combination  with  the  oxygen  of  the 
air,  and  thus  to  compensate  for  the  deficiency.  In  Man  and  other 
animals,  which  can  sustain  considerable  variations  of  climate,  and 
can  adapt  themselves  to  a  great  diversity  of  habits,  the  quantity  of 
carbonic  acid  formed  by  the  direct  combination  of  the  elements  of  the 
food  with  the  oxygen  of  the  air,  will  differ  extremely  under  different 
circumstances.  It  will  serve  as  the  complement  of  that  which  is  formed 
in  other  ways ;  so  that  it  will  diminish  with  the  increase,  and  will 
increase  with  the  diminution,  of  muscular  activity.  On  the  other 
hand,  it  will  vary  in  accordance  with  the  external  temperature  ;  in- 
creasing with  its  diminution,  as  more  heat  must  then  be  generated  ; 
and  diminishing  with  its  increase. — In  all  cases,  if  a  sufficient  supply 
of  food  be  not  furnished,  the  store  of  fat  is  drawn  upon  ;  and  if  this 
be  exhausted,  the  animal  dies  of  cold  (§  117). 

648.  To  recapitulate,  then  ;  the  sources  of  carbonic  acid  in  the  Ani- 
mal body  are  threefold. — 1.  The  continual  decay  of  the  tissues;  which 
is  common  to  all  organized  bodies ;  which  is  diminished  by  cold  and 
dryness,  and  increased  by  warmth  and  moisture  ;  which  takes  place 
with  increased  rapidity  at  the  approach  of  death,  whether  this  affect 
the  body  at  large,  or  only  an  individual  part;  and  which  goes  on  un- 
checked, when  the  actions  of  nutrition  have  ceased  altogether. — 2. 
The  m.etamorphosis,  which  is  peculiar  to  the  Nervous  and  Muscular 
tissues  ;  which  is  the  very  condition  of  their  activity ;  and  which 
therefore  bears  a  direct  relation  to  the  degree  in  which  they  are  ex- 
erted.— 3.  The  direct  conversion  of  the  carbon  of  the  food  into  car- 
bonic acid  ;  which  is  peculiar  to  warm-blooded  animals  ;  and  which 


NATURE  OF  THE  RESPIRATORY  PROCESS.  371 

seems  to  vary  in  quantity,  in  accordance  with  the  amount  of  heat  to 
be  generated. 

649.  Now  the  function  of  Respiration  has  for  its  object,  not  merely 
to  extricate  the  carbonic  acid,  which  is  generated  in  the  system  ;  but 
likewise  to  introduce  the  oxygen,  which  is  required  to  form  that  car- 
bonic acid  ; — the  proportion  of  oxygen  in  the  tissues,  and  in  the  com- 
bustible materials  of  the  blood,  not  being  sufficient  for  this  purpose. 
Hence  it  is  not  enough,  that  the  carbonic  acid  should  be  removed; 
for  this  may  be  accomplished  by  causing  an  animal  to  breathe  an 
atmosphere  which  contains  no  oxygen.  Any  cold-blooded  animal, 
such  as  a  Frog  or  a  Snail,  may  be  kept  in  hydrogen  or  nitrogen  for 
several  hours  or  even  days  ;  and  will  give  out,  during  that  time,  an 
amount  of  carbonic  acid  nearly  as  great  as  if  it  had  been  respiring 
atmospheric  air.  But  the  continued  production  of  carbonic  acid  must 
have  a  limit,  occasioned  by  the  want  of  oxygen,  and  death  will  then 
supervene. — On  the  other  hand,  a  supply  of  oxygen  may  be  freely 
afforded  ;  and  yet  the  presence  of  even  a  small  amount  of  carbonic 
acid  in  the  surrounding  atmosphere  (in  addition  to  that  which  is  nor- 
mally present  in  it,  §  81)  will  impede  the  extrication  of  that  substance 
from  the  blood ;  and  if  the  excess  be  considerable,  the  carbonic  acid 
will  not  be  set  free  at  all ;  so  that  the  same  injurious  results  follow, 
as  if  respiration  were  altogether  prevented  from  taking  place. 

650.  These  two  actions  are  accomplished  by  the  very  same  act ; 
advantage  being  taken  of  the  property  of ''  mutual  diffusion,"  which 
is  common  to  all  gaseous  substances  that  do  not  unite  chemically  with 
one  another.  In  virtue  of  this  property.  Hydrogen,  the  lightest  of 
gases,  and  Carbonic  acid,  one  of  the  heaviest,  when  introduced  into 
the  same  vessel,  will  be  found  in  a  short  time  to  have  uniformly  mixed, 
notwithstanding  the  difference  of  their  specific  gravities,  which  are  as 
1  to  22.  Now  this  intermixture  will  take  place,  when  the  two  gases 
are  separated  by  a  porous  septum;  each  gas  passing  towards  the  other, 
by  an  action  resembling  the  Endosmose  and  Exosmose  of  liquids 
(§  491).  And  it  may  also  take  place,  when  one  of  the  gases  is  dif- 
fused through  a  liquid  ;  provided  that  the  other  gas  is  likewise 
capable  of  being  absorbed  by  the  liquid.  In  this  manner,  as  already 
mentioned,  the  surface  of  venous  blood,  inclosed  in  a  bladder,  may 
be  made  to  exhibit  the  arterial  hue,  by  suspending  the  bladder  in  an 
atmosphere  of  oxygen  ;  for  the  carbonic  acid  of  the  blood,  and  the 
surrounding  oxygen,  will  overcome  by  their  mutual  attraction  the  ob- 
stacle interposed  by  the  bladder ;  and  the  former  will  be  lifted  out, 
so  to  speak,  and  will  be  replaced  by  the  latter.  It  has  been  found  by 
experiment,  that  the  free  carbonic  acid  diffused  through  blood,  may  be 
more  completely  extricated  from  the  liquid,  by  exposing  it  to  hydrogen, 
than  by  placing  it  under  the  vacuum  of  an  air-pump  ;  for  in  the  latter 
case  there  is  nothing  to  replace  it,  and  the  attraction  between  the  gas 
and  the  liquid  tends  to  resist  the  exhausting  influence  of  the  vacuum; 
whilst  in  the  former,  the  blood  receives  one  gas  in  exchange  for  the 


372  ESSENTIAL  STRUCTURE  OF  RESPIRATORY  ORGANS. 

other,  so  that  the  whole  force  of  the  tendency  to  mutual  diffusion  is 
exercised  in  lifting  out  the  carbonic  acid. 

651.  The  immediate  purpose  of  the  organs  of  Respiration,  then, — 
whatever  may  be  the  variety  in  their  form, — is  this :  to  expose  the 
blood  to  the  air,  in  a  state  of  such  minute  division  as  to  present  a  very 
extended  surface,  a  thin  membrane  only  being  interposed  between 
them.  For  this  purpose  we  find  a  certain  organ,  or  set  of  organs, 
specially  set  apart  in  all  the  higher  animals ;  and  this  is  formed  by  a 
prolongation  of  the  general  surface,  either  externallv  or  internally, 
according  to  the  mode  in  which  the  respiration  is  accomplished.  Thus 
in  Fishes  and  aquatic  Mollusks,  the  blood  is  aerated  by  exposure,  not 
directly  to  the  atmosphere,  but  to  the  air  which  is  dissolved  in  the 
water  they  inhabit ;  and  the  respiratory  apparatus  is  formed  in  them 
of  an  extension  of  the  external  surface,  at  a  particular  part,  into  innu- 
merable delicate   fringe-like 

^^g-^- processes,  the  gills  (Fig.  96); 

every  division  of  which  con- 
tains a  network  of  blood- 
vessels (Fig.  100) :  so  that 
the  amount  of  blood,  which 
is  exposed  to  the  surrounding 
medium  at  any  one  time,  is 

collectively  very   great,    al- 

Doris  johnstoni,  showing  the  tuft  of  external  gills.       though  the  quantity  Contained 

in  each  gill-filament  is  very 
minute.  On  the  other  hand,  in  all  the  air-breathing  Vertebrata,  the 
blood  is  exposed  to  the  atmosphere,  through  the  medium  of  aninternal 
membranous  prolongation,  which  is  continuous  with  the  mucous  mem- 
brane lining  the  mouth  and  nostrils  ;  this  forms  a  pair  of  sacs,  termed 
lungs,  communicating  with  the  back  of  the  mouth  by  means  of  a  tube 
called  the  trachea  or  windpipe,  through  which  air  is  freely  admitted 
to  the  cavities  thus  formed  (Fig.  101).  The  blood  is  minutely  dis- 
tributed on  the  walls  of  these  sacs  by  a  close  network  of  capillary 
vessels  (Fig.  102) ;  and  not  only  on  the  external  walls,  but  also  on 
numerous  partitions,  by  which  the  cavities  are  subdivided  with  more 
or  less  minuteness,  so  as  greatly  to  extend  the  vascular  surface. 

652.  Such  is  the  essential  nature  of  the  Respiratory  apparatus ;  but 
in  order  that  it  may  be  carried  into  the  vigorous  operation,  which  is 
required  in  the  higher  classes  of  animals,  various  supplementary 
arrangements  are  made,  for  the  purpose  of  promoting  the  due  influence 
of  the  air  upon  the  blood.  In  the  first  place,  the  capillary  vessels  of 
the  respiratory  surface  are  connected  with  arterial  trunks,  which  issue 
immediately  from  the  heart,  and  which  thus  convey  a  constant  stream 
of  blood  from  that  organ  ;  whilst  they  give  origin  to  venous  trunks, 
which  terminate  directly  in  the  heart,  and  which  are  ready  to  con- 
vey back  to  it  the  blood  that  has  undergone  aeration.  Thus  by  the 
energetic  action  of  the  heart,  and  by  the  force  generated  in  the  capil- 
laries of  the  lungs  (§  598),  a  constant  renewal  is  effected  in  the  blood, 


I 


RESPIRATORY  ORGANS  IN  MOLLUSKS.  373 

■which  is  exposed  to  the  air  through  the  medium  of  these  organs.  On 
the  other  hand,  the  renewal  of  the  blood  would  be  useless,  unless  a 
fresh  supply  of  air  w^ere  continually  being  introduced,  and  that  which 
had  been  vitiated,  by  the  loss  of  its  oxygen  and  the  admixture  of 
carbonic  acid,  were  removed  ;  and  this  is  effected  by  a  series  of  mus- 
cular movements,  which  are  adapted  for  the  alternate  expulsion  of 
the  vitiated  air  from  the  lungs,  and  for  the  introduction  of  a  fresh 
supply  of  pure  air  from  the  atmosphere.  These  movements  are  kept 
up  by  a  certain  part  of  the  nervous  system ;  but  they  are  not  depend- 
ent upon  any  exertion  of  the  will,  for  they  continue  during  profound 
sleep,  and  in  other  states  in  which  even  consciousness  is  altogether 
suspended. 

2.  Different  forms  of  the  Respiratory  Apparatus  in  the  lower  Animals, 

653.  Before  proceeding  to  consider,  in  more  detail,  the  structure 
and  actions  of  the  respiratory  apparatus  in  Man,  we  may  advan- 
tageously glance  at  the  mode  in  which  this  function  is  effected  in  the 
lower  animals. — In  the  lowest  and  simplest,  which  are  inhabitants  of 
the  water,  we  do  not  find  any  special  apparatus  for  the  aeration  of  the 
fluids  of  the  body ;  this  being  accomplished  by  the  exposure  of  them 
to  the  surrounding  medium,  through  the  thin  integument;  and  the 
interchange  of  the  layer  of  water  (holding  air  in  solution)  in  contact 
with  the  aerating  surface,  is  effected  either  by  the  general  movement 
of  the  body,  or  by  the  action  oi  cilia  (§  234),  which  produce  the  cur- 
rents necessary  for  this  purpose.  Not  unfrequently,  the  internal  sur- 
faces— such  as  the  walls  of  the  stomach  and  of  other  cavities, — seem 
as  much  concerned  in  this  function  as  the  external,  or  even  more  so ; 
these  cavities  being  distended  with  water  taken  in  through  the  mouth, 
and  this  water  being  frequently  renewed,  by  the  ejection  of  that  which 
has  been  vitiated,  and  by  the  introduction  of  a  fresh  supply.  This  is 
the  case  in  the  Sea  Anemone,  for  example,  and  in  many  other  Polypes ; 
and  there  are  certain  higher  forms  of  the  same  class,  in  which  there  is 
a  great  dilatation  of  the  pharynx,  which  seems  peculiarly  destined  for 
the  aeration  of  the  fluids, — being  filled  with  water,  and  then  suddenly 
emptied,  at  tolerably  regular  intervals. 

654.  In  the  various  classes  of  the  Molluscous  sub-kingdom,  we 
find  the  respiration  provided  for,  by  the  adaptation  of  distinct  organs 
for  the  purpose.  As  most  of  the  animals  of  this  group  are  inhabi- 
tants of  the  water,  the  respiration  is  usually  carried  on  by  means  of 
gills,  rather  than  by  any  organs  resembling  lungs.  The  latter  is  found, 
however,  in  a  few  species ;  such  as  the  Snail,  Slug,  and  other  terres- 
trial air-breathing  Mollusks  ;  and  usually  consists  of  a  simple  cavity, 
situated  in  the  back,  communicating  directly  with  the  air  through  an 
aperture  in  the  skin,  and  having  its  walls  covered  with  a  minute  net- 
work of  blood-vessels.  The  form  and  position  of  the  gills  differ 
extremely  in  the  several  classes  of  Molluscous  animals.  In  the  lowest, 
the  respiratory  surface  is  formed,  as  in  the  higher  Polypes,  by  a  dila- 


374  RESPIRATORY  ORGANS  IN  MOLLUSKS. 

tation  of  the  Pharynx  ;  but  sometimes,  instead  of  surrounding  a  large 
cavity,  it  forms  a  special  ribbon-like  fold  of  membrane,  passing  from 
one  end  of  it  to  the  other,  on  which  the  blood  is  minutely  distributed. 
In  this  group  of  animals,  there  is  a  regular  system  of  canals  for  the 
conveyance  of  the  blood ;  but  these,  in  many  parts  of  the  system, 
and  especially  on  the  respiratory  membrane,  do  not  seem  to  be  fur- 
nished with  distinct  walls,  and  are  rather  mere  channels  excavated  in 
the  tissues.  And  the  circulation  is  liable  to  a  continual  change  in  its 
direction  ;  the  blood  being  sometimes  transmitted  to  the  respiratory 
surface  hefore  it  proceeds  to  the  body,  and  sometimes  afler  it  has 
traversed  the  other  tissues  (§  557).  The  water  in  contact  with  the 
respiratory  surface  is  continually  renewed  by  the  action  of  the  cilia, 
with  which  it  is  thickly  covered. 

655.  In  certain  other  Mollusks  inhabiting  bivalve  shells,  we  find 
that  the  internal  surface  of  the  mantle  or  skin  that  lines  the  valves,  is 
the  special  organ  of  respiration  ;  the  external  water  having  free  access 
to  these,  by  the  separation  of  the  skin  along  the  edges  of  the  valves, 
so  that  it  enters  the  cavity  in  which  the  viscera  are  lodged,  and  bathes 
their  exterior.  But  in  most  bivalve  Mollusks,  the  internal  surface  of 
the  mantle  is  doubled  (as  it  were)  into  four  ribbon-like  folds,  which 
are  delicately  fringed  at  their  edges,  and  which  have,  in  fact,  the  same 
essential  structure  as  the  gills  of  higher  animals  (§  663).  To  these 
the  blood  is  transmitted,  when  it  has  been  rendered  venous  by  tra- 
versing the  vessels  of  the  body  generally ;  and  in  these  it  is  exposed, 
through  a  surface  which  is  greatly  extended  by  the  minute  division 
of  the  fringes,  to  the  action  of  water  introduced  from  without,  and 
constantly  renewed  by  ciliary  action.  In  many  of  these  animals,  as 
in  the  common  Oyster,  the  two  lobes  of  the  mantle  are  so  completely 
separated,  that  the  water  can  still  enter  freely  between  the  valves ; 
but  in  general,  they  are  more  or  less  united,  so  that  the  cavity  in 
which  the  gills  lie  is  partially  closed.  There  is  always  a  provision, 
however,  for  the  free  access  of  water  from  without,  by  means  of  two 
apertures,  one  for  its  entrance  and  the  other  for  its  ejection;  and  in 
certain  species  which  burrow  deeply  in  sand  or  mud,  these  apertures 
are  furnished  with  long  tubes,  or  siphons,  which  convey  the  water 
from  nearer  the  entrance  of  the  burrow,  and  carry  it  thither  again. 
In  these,  also,  a  continued  flow  of  water  over  the  respiratory  surface 
is  maintained  by  the  vibration  of  the  cilia,  with  which  they  are 
clothed. 

656.  The  position  of  the  gills,  in  the  Mollusca  of  higher  organiza- 
tion, is  extremely  variable.  Sometimes  they  are  disposed  upon  the 
external  surface  of  the  body,  and  form  delicate  leaf-like  or  arbores- 
cent appendages  (Fig.  97);  whilst  in  other  cases  they  are  enclosed  in 
a  special  cavity  or  gill-chamber,  to  which  water  is  freely  admitted 
from  without ;  a  continual  interchange  being  provided  for,  either  by 
ciliary  action,  or  by  muscular  movements  specially  adapted  for  the 
purpose.  The  blood  is  conveyed  to  them,  after  having  become 
venous  in  traversing  the  capillaries  of  the  general  system,  by  means 


RESPIRATORY  ORGANS  IN  WORMS  AND  CRUSTACEA. 


375 


Fig.  97. 


One  of  the  arborescent  pro- 
cesses, forming  the  gills  of 
Doris  Johnstoni  separated  and 
enlarged. 


of  large  channels  and  sinuses  excavated  in  the  several  parts  of  the 
body  (§  556) ;  and  after  being  aerated  in  the  gills,  it  returns  to  the 
heart,  to  be  again  conveyed  to  the  system.  In  the  Cuttle-fish  tribe, 
there  are  supplementary  hearts  at  the  origin  of 
the  branchial  arteries, — or  vessels  that  distri- 
bute blood  to  the  gills ;  and  these  have  evi- 
dently for  their  purpose,  to  render  the  respira- 
tory circulation  more  energetic,  and  thus  to 
increase  the  aeration  of  the  blood,  in  the  de- 
gree required  for  the  vigorous  habits  of  these 
animals,  which  present  a  remarkable  contrast 
to  the  sluggish  inert  character  of  the  Mollusca 
in  general. — In  these  classes,  taken  as  a  whole, 
the  respiration  is  low  in  its  amount.  The 
blood  contains  no  red  corpuscles,  excepting 
perhaps  in  the  highest  class;  and  the  change 
in  its  composition,  which  is  effected  by  the  air, 
is  confined,  therefore,  to  the  fluid  plasma,  or 
liquor  sanguinis.  And  as  it  is  not  exposed 
directly  to  the  air,  except  in  a  few  species,  but  to  the  air  contained 
in  the  water  inhabited  by  the  animals,  this  change  cannot  be  very 
energetically  performed.  But  as  the  life  of  these  animals  is  chiefly 
vegetative, — as  their  movements,  except  in  the  highest  classes,  are 
few  and  feeble, — and  as  they  maintain  no  independent  heat, — there 
is  but  little  need  of  the  interchange,  which  it  is  the  object  of  the  re- 
spiratory process  to  effect ;  and  these  animals  can  sustain  the  complete 
suspension  of  it  for  a  long  time. 

657.  Among  many  of  the  Articulated  tribes,  the  respiration  is  car- 
ried on  upon  a  similar  plan.  In  some  of  the  lowest,  such  as  the  Tape- 
worm of  the  intestinal  canal,  there  is  no  special  provision  for  the 
aeration  of  the  fluids ;  the  soft  integument  permitting  the  extrication 
of  carbonic  acid,  and  imbibition  of  oxygen,  in  the  required  degree. 
This  is  but  very  small,  however ;  the  life  of  these  animals  being 
almost  purely  vegetative.  In  the  Marine  Worms,  which  constitute  a 
numerous  and  interesting  group,  endowed  with  considerable  loco- 
motive powers,  and  leading  a  life  of  almost  constant  activity,  there  is, 
on  the  other  hand,  a  special  provision  for  this  function ;  the  blood 
being  transmitted,  in  the  course  of  its  circulation,  to  a  series  of  gill- 
tufts,  which  are  composed  of  a  delicate  membrane  prolonged  from  the 
external  surface  of  the  body,  and  which  sometimes  have  the  form  of 
branching  trees,  and  sometimes  of  delicate  brushes  made  up  of  a  bun- 
dle of  distinct  filaments.  In  either  case,  the  filaments  are  traversed 
by  blood-vessels,  and  are  adapted  to  bring  the  blood  into  close  rela- 
tion with  the  surrounding  water ;  and  the  continual  interchange  of 
the  latter  is  provided  for  by  the  restless  movements  of  the  body. 
The  tufts  are  sometimes  arranged  along  every  segment  of  the  body ; 
and  their  multiplication  prevents  them  from  individually  attaining  any 
considerable  size.     In  other  cases,  they  are  disposed  at  intervals; 


376 


RESPIRATORY  ORGANS  IN  CRUSTACEA  AND  INSECTS. 


and  they  are  then  larger,  being  less  numerous.  Their  most  beautiful 
development  is  where  they  are  present  on  the  head  only,  the  rest  of 
the  body  being  enclosed  in  a  shelly  or  sandy  tube,  as  in  the  Serpiila 
and  Terehellce.  The  gill-tufts  then  frequently  present  the  appearance 
of  a  flower,  endowed,  when  alive,  with  the  most  brilliant  and  delicate 
hues.  In  many  animals  of  this  group,  there  is  a  small  supplementary 
heart  at  the  base  of  every  one  of  the  vessels,  that  distribute  the  blood 
to  the  gills ;  and  this  is  obviously  designed  to  aid  in  the  respiratory 
circulation,  for  which  the  feeble  action  of  the  dorsal  vessel  w6uld 
not  furnish  sufficient  power  (§  552). 

658.  The  higher  Articulated  classes  are,  for  the  most  part,  adapted 
to  atmospheric  respiration,  on  the  plan  to  be  presently  explained  ; 
but  there  is  one  class,  that  of  Crustacea,  whose  respiration  is  still 
carried  on  through  the  medium  of  water.  In  the  lowest  forms  of  this 
group,  there  is  no  special  respiratory  apparatus ;  the  general  surface 
being  soft  enough  to  admit  of  the  required  aeration  of  the  fluids 
through  its  own  substance,  and  the  animal  functions  being  performed 
with  so  little  activity,  that  a  very  small  amount  of  interchange  is 
required.  In  the  higher  orders,  however,  whose  bodies  are  encased 
within  a  hard  envelop,  we  find  external  gills,  like  those  of  many 
Mollusks ;  and  these  are  attached  to  the  most  movable  parts  of  the 
body, — one  or  more  pairs  of  legs  being  in  some  instances  kept  in  con- 
stant agitation,  for  the  purpose  of  producing  currents  in  the  surround- 
ing fluid,  that  may  serve  for  the  aeration  of  the  blood.  In  the  Crab- 
tribe,  which  constitutes  the  highest  family  of  this  class,  the  gills  are 
themselves  enclosed  within  a  cavity,  formed  by  a  sort  of  doubling  of 
the  hard  integument  of  the  under  side  of  the  body  ;  and  a  constant 
stream  of  water  is  maintained  through  this,  by  means  of  a  peculiar 
valve,  situated  in  the  exit-pipe  ;  the  continual  movement  of  the  valve 
causing  a  regular  stream  of  water  to  issue  from  the  gill-chamber,  and 
thus  occasioning  the  entrance  of  a  constantly  fresh  supply.  In  these, 
also,  we  find  a  dilatation,  the  walls  of  which  seem  to  have  contractile 
powers,  at  the  commencement  of  each  artery  that  distributes  the 
blood  to  the  gills  ;  and  this  collects  the  venous  blood  from  the  various 
channels,  in  which  it  has  meandered  through  the  body.  It  is  by  the 
enclosure  of  the  gills  within  a  cavity,  and  by  the  consequent  protec- 
tion of  them  from  the  drying  influence  of  the  air  (which  would  prevent 
their  function  from  being  duly  performed),  that  Crabs  and  other  allied 
species  are  enabled  to  live  for  a  considerable  time  out  of  water ;  and 
the  Land-Crabs,  as  they  are  termed,  are  adapted  to  spend  the  greater 
part  of  their  lives  at  a  distance  from  the  sea,  by  means  of  a  special 
glandular  apparatus  within  the  gill-cavity,  which  secretes  a  fluid  that 
preserves  the  surface  of  the  gills  in  the  moist  condition,  requisite  for 
the  aeration  of  the  blood  through  its  membrane.  Thus  the  Land- 
Crabs  are  air-breathing  animals  (except  at  certain  seasons,  when  they 
frequent  the  sea-shores),  although  they  breathe  by  gills. 

659.  In  Insects  and  other  proper  air-breathing  Articulata,  however, 
the  character  of  the  respiratory  apparatus  is  very  diflferent.    The  transi- 


RESPIRATORY  ORGANS  IN  INSECTS. 


377 


tion  from  one  form  to  the  other  is  effected  through  such  animals  as 
the  Leech  and  the  Earthworm,  which  seem  able  to  breathe  either  air 
or  water.  These  are  furnished  with  a  series  of  small  sacs,  disposed 
at  regular  intervals  along  each  side  of  the  body,  and  opening  by  a 
row  of  pores,  which  are  termed  spiracles  or  stigmata.  The  blood- 
vessels are  distributed  upon  the  walls  of  these  sacs ;  and  either  air 
or  water  may  be  introduced  into  their  interior,  by  the  movements  of 
the  body,  which  ^re  adapted  to  compress  their  walls,  and  then  to 
allow  them  to  dilate.  In  the  Centipedes  and  their  allies,  these  air- 
sacs  send  out  prolongations;  which  have  not,  however,  any  very 
ready  communication  with  each  Mher.  But  in  insects,  the  spiracles, 
instead  of  forming  the  en- 
trances to  so  majiy  distinct  ^^^  Tig.ds.  ^ 
sacs,  open  into  a  pair  of  large 
tubes,  one  of  which  traverses 
the  body  on  either  side, 
along  its  whole  length. 
These  tubes,  termed  ^racAets, 
have  many  communications 
with  each  other  across  the 
body ;  and  they  branch  out 
into  innumerable  prolonga- 
tions, the  ultimate  ramifica- 
tions of  which  are  distributed 
to  every  portion  of  the  sys- 
tem. They  occasionally 
present  dilatations  of  con- 
siderable size  (Fig.  98,  a.)  ;  especially  in  the  thoracic  region  of  the 
body,  in  those  insects,  which  are  endowed  with  great  powers  of  flight. 
These  dilatations  or  air-sacs  appear  destined  to  serve  as  reservoirs  of 
air,  during  the  time  that  the  insect  is  upon  the  wing,  its  spiracles 
being  then  partially  closed  ;  and  they  may  also  be  useful  in  diminish- 
ing the  specific  gravity  of  the  body.  The  air-tubes  are  prevented 
from  having  their  cavity  obliterated  through  the  pressure  of  the  sur- 
rounding parts,  by  means  of  an  elastic  spiral  fibre ;  which  winds 
round  them,  between  their  outer  and  inner  membrane,  from  one  ex- 
tremity to  the  other  (Fig.  98,  b.)  ;  and  which  answers  the  purpose  of 
the  cartilaginous  rings  and  plates,  in  the  trachea  and  bronchi  of  air- 
breathing  Vertebrata. 

660.  In  this  manner,  the  air  that  is  introduced  through  the  spiracles 
is  carried  into  every  part  of  the  body,  and  is  brought  into  immediate 
relation  with  the  tissues  to  be  aerated ;  so  that  the  carbonic  acid 
which  they  set  free  is  communicated  at  once  to  the  atmosphere,  in- 
stead of  being  taken  up  by  the  blood  ;  and  the  oxygen  they  require  is 
imbibed  in  the  same  manner.  And  thus  we  see  how  the  respiration 
of  this  interesting  class,  which  is  unequaled  for  its  energy  when  the 
body  is  in  a  state  of  activity,  is  provided  for  without  an  active  circu- 
lation of  blood,  and  without  the  presence  of  red  corpuscles, — which 


Respiratory  apparatus  of  insects:— a,  air  vesicles  and 
part  of  tracheal  system  of  Scolia  hortorum.  b,  portion  of 
one  of  the  great  longitudinal  tracheae  of  Carabus  aurattis, 
with  one  of  its  spiracles. 


378  COMPARATIVE  FORMS  OF  RESPIRATORY  APPARATUS. 

elsewhere  seem  to  be  essential  conditions  of  the  interchange  of  oxygen 
and  carbonic  acid  between  the  air  and  the  tissues,  wherever  this  takes 
place  to  any  great  extent. 

661.  In  the  Spider  tribe,  w-e  return  to  a  more  concentrated  form  of 
the  respiratory  apparatus ;  but,  notwithstanding  that  it  is  limited 
within  much  narrower  dimensions  externally,  it  exposes  a  very  large 
amount  of  surface  on  its  interior.  It  consists  of  a  series  of  sacs,  much 
less  numerous  than  in  the  lower  Articulata,  and  not  communicating 
with  each  other.  Their  lining  membrane,  however,  is  doubled  into 
a  series  of  folds,  which  lie  in  proximity  with  each  other,  like  the 
leaves  of  a  book,  and  which  thus  firesent  a  very  extensive  surface 
wathin  a  very  small  space.  Over  this  surface,  the  blood  is  distributed 
in  a  minute  capillary  network ;  and  thus  it  comes  into  immediate  re- 
lation with  the  air,  which  is  received  into  the  cavity  through  its  aper- 
ture or  spiracle.  The  alternate  admission  and  expulsion  of  air  seem 
to  be  provided  for,  as  in  Insects,  by  movements  of  the  body,  which 
first  empty  the  cavities  or  air-tubes  by  compression,  and  then  allow 
them  to  be  re-filled  by  their  own  elasticity,  the  pressure  being  relaxed. 
The  respiratory  cavities  in  the  Spider-tribe  have  received  the  name  of 
'pulmonary  branchice  ;  from  their  analogy,  on  the  one  hand,  with  the 
lungs  of  higher  animals  ;  and,  on  the  other,  with  the  branchial  or  gill- 
cavity  of  the  higher  Crustacea,  the  gills  in  which  are  formed  by  pro- 
longations of  the  lining  membrane,  like  the  leaf-like  folds  in  the  air- 
cavities  of  the  Spider-tribe. 

662.  The  accompanying  diagram  will  give  an  idea  of  the  relations  of 
these  different  forms  of  the  respiratory  apparatus,  amongst  themselves, 
and  to  that  of  Vertebrata.     Let  the  line  a  b  represent  the  general 

Fig.  99. 


Diagram  illustrating  different  forms  of  the  Respiratory  apparatus :— a,  simple  leaf-like  gill ;  b,  simple 
respiratory  sac ;  c,  divided  gill ;  rf,  divided  sac ;  e,  pulmonary  branchia  of  Spider. 

surface  of  the  animal ;  the  continuations  of  that  line  on  its  upper  side 
being  its  external  prolongations;  and  those  below,  its  internal  pro- 
longations or  reflexions.  Now  at  a  is  seen  the  character  of  the  simple 
foliaceous  or  leaf-like  gill,  such  as  is  found  in  the  lower  aquatic  ani- 
mals ;  presenting  merely  a  flat  expanded  surface  in  contact  with  the 
water,  over  which  the  blood  may  be  distributed.  At  b  is  shown  a 
correspondingly  simple  inversion  ;  such  as  that  which  forms  the  re- 
spiratory sac  of  the  leech,  having  the  blood-vessels  distributed  upon 
its  walls.     A  higher  form  of  the  gill,  such  as  is  found  in  fishes  and 


RESPIRATORY  ORGANS  OF  FISHES.  379 

in  the  higher  aquatic  Invertebrata,  is  seen  at  c;  the  surface  being 
greatly  extended,  by  subdivision  into  minute  filaments.  A  more 
complex  form  of  the  pulmonary  apparatus,  such  as  is  found  in  the 
higher  Vertebrata,  is  shown  at  d;  the  blood  being  distributed,  not 
merely  to  its  outer  walls,  but  to  the  minute  partitions  which  subdivide 
its  cavity  into  cells.  And  at  e  is  represented  the  respiratory  organ  of 
the  Spider-tribe  ;  which  bears  an  obvious  resemblance  to  the  lung  of 
the  Vertebrated  animal,  show^n  at  d  ;  whilst  it  is  evidently  as  nearly 
allied  to  the  gill  shown  at  c,  provided  this  be  imagined  to  be  sunk 
within  a  cavity  formed  by  a  depression  of  the  external  surface,  instead 
of  projecting  beyond  it. — Thus  we  see  how  very  close  is  the  real 
resemblance  between  all  the  forms  of  the  respiratory  apparatus ;  how- 
ever unlike  each  other  they  may  at  first  sight  appear  to  be. 

663.  The  gills  of  Fishes  correspond  with  those  of  the  higher  Mol- 
lusca  in  all  essential  particulars;  but  they  are  more  largely  developed 
in  proportion  to  the  size  of  the  body  ;  and  they  are  placed  in  a  situa- 
tion that  enables  them  to  receive  a  more  regular  and  constantly- 
changed  supply,  both  of  blood  and  water.  The  gills  are  suspended 
to  bony  or  cartilaginous  arches,  of  which 
three,  four,  or  more,  are  fixed  on  either  side  Fig.  loo. 

of  the  neck ;  and  the  fringes  hang  loosely 
within  a  cavity,  which  communicates  on  the 
one  hand  with  the  mouth,  and  on  the  other 
with  the  exterior  of  the  body.  The  mechan- 
ism of  respiration  is  very  complex  in  these 
animals;  and  is  evidently  adapted  to  produce 
the  most  effectual   aeration  possible.      The 

mouth    is  first  distended    with    water  ;    and    its  ^apniary  network  of  a  pair 

muscles  are  then  thrown  into  contraction,  in     of  leaflets  of  the  giiis  of  the 

,  .  1    .,  i         ii  1  Eel: — a,   a,   branches   of  the 

such  a  manner  as  to  expel  the  water,  through       branchial     anery     conveying 

the  aperture  on  either  side  of  the  pharynx,  jrSranctaf  \t'in!' retu^Sl 
into  the  gill-cavity.     At  the  same  time,  the     atirated  biood  The  disappear- 

p  i«^      1  I  1     /.  anceof  the  dark  shading  in  the 

bony  arches   are  lifted    and  separated  from     network,  as  it  traverses  the 

f        .,  1        ii  .'  c  ^  gi'l'  is  designed  to  indicate  the 

each  other,  by  the  action  Ot  muscles  espe-  change  in  the  character  of  the 
Cially    adapted    to    this    purpose;     so    that    the        Jloodas^^  passes  from  one  side 

gill-fringes  may  hang  freely,  and  may  present 

no  obstacle  to  the  flow  of  the  water  between  them.  When  they  have 
been  thus  bathed  with  the  aerating  liquid,  and  their  blood  has  under- 
gone the  necessary  change,  the  water  is  expelled  through  the  out- 
ward aperture  on  each  side  of  the  back  of  the  neck ;  which  is  fur- 
nished with  a  large  flap  or  valvular  cover  termed  the  operculum.  In 
some  of  the  cartilaginous  Fishes,  each  branchial  arch  is  inclosed  in  a 
separate  cavity ;  which  communicates  on  the  inner  side  with  the  pha- 
rynx by  an  orifice  peculiar  to  itself,  and  by  another  orifice  with  the 
external  surface.  Thus  there  is  a  series  of  external  openings,  instead 
of  a  single  one,  on  each  side  of  the  neck;  and  these  sometimes  amount 
to  six  or  seven,  as  in  the  Lamprey,  reminding  us  of  the  spiracles  of 
Articulated  animals ;  whilst  there  is  a  corresponding  series  of  internal 


380  RESPIRATORY  ORGANS  OF  FISHES. 

openings  into  the  pharynx  on  either  side,  or  into  a  tube  that  commu- 
nicates with  it. 

664.  It  is  well  known,  that  most  Fishes  speedily  die  when  removed 
from  the  water  ;  and  it  can  be  easily  shown,  that  the  deficient  aeration 
of  the  blood  is  the  immediate  cause  of  their  death.  But  as  it  might 
have  been  expected,  that  the  atmosphere  would  exert  a  much  more 
energetic  influence  upon  the  blood  contained  in  the  gills,  than  that 
which  is  exercised  by  the  air  contained  in  the  water,  the  question 
naturally  arises,  how  this  deficient  aeration  comes  to  pass.  It  is 
chiefly  due  to  the  two  following  causes ;  the  drying  up  of  the  mem- 
brane of  the  gills  themselves,  where  it  is  exposed  to  the  air,  so  that 
the  aeration  of  the  blood  is  impeded ; — anc^  the  flapping  together  of 
the  filaments  of  the  gills,  which  no  longer  hang  loosely  and  apart,  but 
adhere  in  such  a  manner  as  to  prevent  the  exposure  of  the  greater 
portion  of  their  surface  to  the  air.  Those  fishes  live  longest  out  of 
water,  in  which  the  external  gill-openings  are  very  small,  so  that  the 
gill-cavity  may  be  kept  full  of  fluid ;  and  there  are  certain  species 
which  are  provided  like  the  Land-crab,  with  a  particular  apparatus 
for  keeping  the  gills  moist,  and  which  perform  long  migrations  over 
land  in  search  of  food,  even  (it  is  said)  ascending  trees.  These  are 
exceptions  to  the  general  rule. 

665.  The  respiration  of  Fishes  is  much  more  energetic  than  that 
of  any  of  the  lower  aquatic  animals ;  and  this  is  partly  due  to  the 
great  extension  of  the  surface  of  the  gills,  partly  to  the  provision  just 
explained  for  maintaining  a  constant  flow  of  fresh  water  over  their 
surface,  and  partly  to  the  position  of  the  heart  at  the  base  of  the  main 
trunk  that  conveys  the  blood  to  the  gills  (§  558),  by  which  the  regu- 
lar propulsion  of  that  fluid  through  these  organs  is  secured.  Their 
blood,  too,  is  furnished  with  red  corpuscles;  which  give  important 
aid  in  conveying  oxygen  from  the  gills  to  the  remote  tissues  of  the 
body,  and  in  returning  the  carbonic  acid  to  be  excreted.  The  pro- 
portion of  these  varies  considerably,  in  the  diflferent  species  of  the 
class,  being  very  small  in  those  that  approach  most  nearly  to  the 
Invertebrata ;  and  there  is  even  an  entire  absence  of  them  in  one 
remarkable  fish,  the  Amphioxus  or  Lancelot ;  whilst  they  are  pre- 
sent in  large  numbers  in  the  blood  of  certain  Fishes,  which  have 
great  muscular  activity,  and  can  maintain  a  high  independent  tem- 
perature. 

666.  It  would  seem,  however,  that  not  even  this  high  amount  of 
respiration  is  always  suflficient  for  Fishes,  which  live  in  small  col- 
lections of  water,  where  their  temperature  is  liable  to  be  greatly 
augmented  by  the  heat  of  summer ;  under  which  condition,  there  is 
an  increased  proneness  to  disintegration  in  their  tissues,  and  a  cor- 
responding necessity  for  the  extrication  of  carbonic  acid  and  for  the 
absorption  of  oxygen.  Many  fresh-water  fishes  under  such  circum- 
stances, may  be  seen  to  come  to  the  surface  and  to  swallow  air ;  and  it 
would  seem  as  if  the  interior  of  the  intestinal  canal  then  served  the 
purpose  of  a  respiratory  surface,  the  air  being  expelled  from  the  anus, 


RESPIRATORY  ORGANS  OF  FISHES  AND  REPTILES.  381 

deprived  of  a  large  part  of  its  oxygen,  and  highly  charged  with  car- 
bonic acid. 

667.  In  addition  to  their  apparatus  for  aquatic  respiration,  many 
Fishes  are  provided,  in  their  air-bladder^  with  the  rudiments  of  the 
air-breathing  apparatus  of  higher  animals;  although  it  is  only  in  cer- 
tain species,  which  approach  Reptiles  in  their  general  organization, 
that  this  really  affords  any  aid  in  the  aeration  of  the  blood.  The 
air-bladder  in  its  simplest  condition  is  entirely  closed ;  and  it  is  then 
obviously  incapable  of  taking  any  share  in  the  respiratory  function, 
although  it  seems  to  be  an  organ  of  some  importance  to  the  animal,  in 
regulating  its  specific  gravity,  and  altering  its  position  in  the  water. 
In  other  cases,  it  communicates  with  the  intestinal  tube  by  a  short 
wide  canal,  termed  the  ductus  pneumaticus ;  and  this  may  serve  to 
admit  air,  which  is  taken  into  the  alimentary  tube  by  the  process  of 
swallowing  just  mentioned.  In  the  Sauroid  Fishes,  just  adverted  to, 
the  air-bladder  forms  a  double  sac,  which  is  evidently  the  repre- 
sentative of  the  double-lung  of  the  air-breathing  Vertebrata ;  and  it 
communicates  with  the  back  of  the  mouth  by  a  regular  trachea  or 
windpipe,  which  has  a  muscular  valve  at  its  commencement,  serving 
to  open  or  close  its  orifice.  Some  of  these  fishes  are  able  to  live  for 
a  considerable  time  out  of  water,  their  respiration  being  maintained 
by  these  rudimentary  lungs  ;  and  they  can  also  make  a  hissing  sound, 
by  the  expulsion  of  the  air-sacs  through  the  narrow  glottis,  or  entrance 
to  the  trachea. 

668.  The  condition  of  the  Respiratory  apparatus,  and  the  mode  in 
which  the  function  is  performed,  in  the  class  of  Reptiles,  are  peculiarly 
interesting;  as  it  is  in  this  class,  that  we  first  meet  with  the  complete 
adaptation  of  the  Vertebrated  structure  to  the  aeration  of  the  blood  by 
the  direct  influence  of  the  atmosphere.  Their  general  habits  of  life 
require  but  a  very  feeble  amount  of  aeration,  especially  at  moderate 
temperatures ;  their  muscular  and  nervous  systems  being  usually  exer- 
cised in  a  very  low  degree ;  their  movements  being  sluggish,  and  their 
perceptions  obtuse.  In  fact,  they  may  be  considered,  on  the  whole, 
as  the  most  vegetative  of  all  Vertebrated  animals.  In  accordance 
with  this  character,  the  lungs  are  so  constructed,  as  not  to  expose  any 
very  large  amount  of  blood  to  the  air  at  any  one  time;  and,  as  we 
have  already  seen  (§  563),  only  a  portion  of  the  stream  of  the  circu- 
lation is  diverted  to  the  lungs ;  the  main  current  being  sent  to  the 
system  with  only  that  amount  of  aeration,  which  it  has  derived  from 
the  admixture  of  the  portion  of  blood  that  has  been  aerated  in  the 
lungs,  with  the  venous  current  that  has  last  been  returned  from  the 
system. 

669.  The  lungs  of  Reptiles  are,  for  the  most  part,  capacious  sacs, 
occupying  a  considerable  part  of  the  cavity  of  the  trunk;  but  they  are 
very  slightly  subdivided,  so  that  the  amount  of  surface  they  can 
expose  is  really  small.  Where  any  subdivision  exists,  it  is  usually  at 
the  upper  extremity  of  the  lung,  near  the  point  of  entrance  of  the 
bronchial  tube ;  and  where  there  is  no  actual  subdivision  of  the  cavity, 


382 


RESPIRATORY  ORGANS  OF  REPTILES. 


Fig.  101. 


Section  of  the  Lung  of  the  Turtle. 


we  usually  find  that  its  surface  is  extended  in  this  situation,  by  the 
formation  of  a  number  of  little  depressions  or  pouches  in  its  walls, 
upon  which  the  blood-vessels  are  minutely  distributed.  The  greatest 
amount  of  subdivision  is  seen  in  the  lungs  of  the  Turtle  tribe ;  but 

even  in  these,  the  partitions  scarcely  form  a 
complete  division  at  any  part  of  the  lungs; 
and  the  ultimate  air-cells  are  of  very  large 
size.  The  air-sacs  of  Reptiles  are  not  filled, 
like  those  of  Mammalia,  by  an  act  of  inspi- 
ration, but  by  a  process  of  swallowing, 
which  is  comparatively  tedious  ;  and,  from 
the  small  amount  of  aerating  surface,  in 
proportion  to  the  amount  of  air  thus  re- 
ceived into  the  cavity,  one  inflation  of  the 
air-sacs  lasts  for  a  considerable  time.  When 
the  replacement  of  oxygen  by  carbonic  acid 
has  proceeded  to  an  extent  that  renders  the 
air  no  longer  fit  to  remain  in  the  lungs,  these 
cavities  are  emptied  by  pressure  exercised 
upon  them  by  the  muscles  of  the  trunk ;  and 
the  slow  exit  of  the  air  through  the  narrow 
glottis  is  accompanied  by  a  prolonged  hiss- 
ing sound,  which  is  the  only  sort  of  voice 
that  is  possessed  by  the  greater  part  of  the 
Reptile  class.  The  lungs  are  again  filled  by  the  swallowing-process ; 
and  all  goes  on  as  before. 

670.  Now  in  the  Frog  tribe,  which  forms  the  lowest  order  of  Rep- 
tiles (and  which  is  sometimes  ranked  as  a  distinct  class,  under  the 
title  of  Amphibia),  the  respiration,  during  the  early  or  Tadpole  state, 
is  aquatic  ;  being  carried  on  by  means  of  gills,  and  conducted  exactly 
upon  the  plan  of  that  of  Fishes.  The  lungs  are  not  developed,  until 
a  period  long  subsequent  to  the  animal's  emersion  from  the  egg; 
and  as  soon  as  they  are  ready  to  come  into  play,  an  alteration  begins 
to  take  place  in  the  circulating  system,  by  which  the  current  of  blood 
is  diverted  towards  them,  and  away  from  the  gills  (§  562).  This 
change  takes  place  to  its  full  extent  in  the  Frog,  Toad,  Newt,  and 
their  allies  ;  which  henceforth  have  a  respiration  and  a  circulation 
exactly  analogous  to  that  of  Reptiles  in  general ;  but  it  is  checked 
in  the  Proteus,  Siren,  and  other  species,  which  form  the  perenni- 
branchiate  group, — so  called  from  the  persistent  character  of  their 
gills,  which  still  remain  in  action,  the  lungs  never  being  sufficiently 
developed  to  maintain  the  respiration  by  themselves.  The  curious 
influence  which  Light  possesses  on  this  metamorphosis,  has  been 
already  referred  to  (§  95). 

671.  This  order  Batrachia  is  further  distinguished  from  other  Rep- 
tiles, even  when  the  metamorphosis  is  complete,  by  the  softness  and 
nakedness  of  the  skin  ;  which  is  destitute  of  the  scales  and  horny 
plates,  that  cover  it  in  the  Lizards,  Serpents,  and  Tortoises.     The 


RESPIRATION  IN  REPTILES  AND  BIRDS.  383 

skin  of  the  Frog  tribe  is  a  very  important  organ  of  respiration;  being 
richly  supplied  with  blood-vessels;  and  exposing  their  contents  to  the 
influence  of  the  air,  under  circumstances  nearly  as  favourable  as  those 
afforded  by  the  imperfectly-developed  lungs  of  these  animals.  Thus  a 
Frog,  from  which  the  lungs  have  been  removed,  will  live  a  consider- 
able time  at  a  moderate  temperature,  if  its  skin  be  freely  exposed  to 
a  moist  air ;  for  in  consequence  of  the  peculiar  mode  in  which  the 
circulation  is  carried  on  in  these  animals  (§  562),  the  interruption  to 
the  flow  of  blood  through  the  lungs  does  not  (as  in  the  higher  classes) 
produce  a  stagnation  of  the  general  current  through  the  body;  and  the 
blood  receives,  in  its  course  through  the  skin,  a  sufficient  amount  of 
aeration  for  the  support  of  life.  Indeed  at  a  low  temperature,  the 
influence  of  water  on  the  skin  is  sufficient  (by  means  of  the  air 
included  in  the  liquid)  to  remove  the  small  amount  of  carbonic  acid 
then  ready  for  excretion,  and  to  supply  the  requisite  amount  of 
oxygen;  and  Frogs  may  thus  live  beneath  the  water  for  any  length  of 
time,  without  coming  to  the  surface  to  breathe.  But  with  the  rise  of 
the  temperature  of  their  bodies,  their  blood  requires  a  higher  degree 
of  aeration ;  and  they  then  come  to  the  surface  to  take  in  air  by  the 
mouth,  w^hich  aerates  the  blood  through  the  lungs.  It  appears  that, 
during  the  heat  of  summer,  the  pulmonary  respiration,  and  the  influ- 
ence of  the  water  on  the  skin,  are  not  sufficient;  as  it  is  found  that 
Frogs  die,  if  they  are  confined  to  the  water  under  such  circumstances, 
— their  natural  habit  being  to  quit  the  water  at  such  times,  so  that  the 
air  may  exert  its  full  influence  on  their  skin  as  well  as  on  their  lungs. 
They  do  not,  however,  quit  the  neighbourhood  of  water,  and  soon 
die  if  exposed  to  a  dry  atmosphere ;  for  if  the  skin  become  dry,  its 
aerating  function  can  be  no  longer  performed.  The  same  result 
happens,  if  the  passage  of  gases  through  the  skin  be  impeded  by 
smearing  it  over  with  any  unctuous  substance.  We  shall  presently 
find  reason  to  believe,  that  this  cutaneous  respiration  is  a  very  im- 
portant part  of  the  function,  even  in  Man  and  the  Mammalia. 

672.  The  class  of  Birds  presents  a  most  striking  contrast  to  that  of 
Reptiles,  in  regard  to  the  energy  of  the  respiratory  function,  and  the 
extent  of  the  apparatus  destined  to  its  performance.  The  lungs  in 
these  animals  undergo  a  minute  subdivision ;  so  that  the  extent  of 
surface,  over  which  they  expose  the  blood  to  the  air,  is  greatly  in- 
creased. But  this  subdivision  is  not  carried  to  the  same  degree  of 
minuteness  as  it  is  in  Mammalia ;  and  the  required  extent  of  surface 
would  not  be  afforded  by  the  lungs  alone.  In  addition  to  these  organs, 
we  find  large  air-sacs,  communicating  with  them,  disposed  in  different 
parts  of  the  body, — such  as  the  abdominal  cavity,  the  interspaces 
among  the  muscles,  the  spaces  between  the  muscles  and  the  skin,  &c. 
These  very  greatly  increase  the  respiratory  surface ;  their  lining  mem- 
brane being  extremely  vascular,  and  adapted  to  expose  the  blood  to 
the  influence  of  the  air.  In  most  Birds,  the  bones  themselves  are 
hollow ;  and  the  lining  membrane  of  their  cavities  serves  as  an  addi- 
tional aerating  surface,  the  air  being  introduced  into  the  interior  of 


384  RESPIRATION  IN  BIRDS. 

the  bones,  by  canals  that  communicate  directly  with  the  lungs.  So 
free  is  this  communication,  that  the  respiration  has  been  known  to  be 
maintained  through  the  fractured  humerus  of  an  Albatross,  w^hen  an 
attempt  was  made  to  destroy  the  bird  by  compressing  its  trachea. 
Thus  the  respiratory  surface  is  extended  into  the  remoter  parts  of  the 
system,  very  much  as  in  Insects ;  and  the  hollowness  of  the  bones, 
together  with  the  presence  of  numerous  air-sacs  in  different  parts  of 
the  body,  contribute  to  diminish  its  specific  gravity.  The  large  quan- 
tity of  air  thus  included  in  different  portions  of  the  frame,  also  serves, 
like  that  contained  in  the  air-sacs  of  Insects,  as  a  reservoir  for  the 
supply  of  the  principal  aerating  organs  during  active  flight,  when  the 
respiratory  movements  are  less  free. 

673.  The  mechanism  of  Respiration  in  Birds  is  very  different  from 
that  w^hich  produces  the  respiratory  movements  in  Mammalia.  The 
cavities  of  the  chest  and  thorax  are  not  yet  separated  by  a  diaphragm ; 
except  in  a  very  small  number  of  species,  that  approach  most  nearly 
to  the  next  class.  But,  on  the  other  hand,  the  w^hole  cavity  of  the 
trunk  is  more  completely  enclosed  in  a  bony  casing;  the  ribs  being 
connected  with  the  sternum  by  osseous  prolongations  from  the  latter, 
instead  of  by  cartilages;  and  the  sternum  itself  being  so  largely  de- 
veloped, as  to  cover  almost  the  entire  front  of  the  body.  Now  the 
natural  condition  of  this  bony  framework  is  such,  that  when  no  pres- 
sure is  made  upon  it,  the  cavity  it  encloses  is  in  a  state  of  distension ; 
and  the  state  of  emptiness  can  only  be  produced  by  a  forcible  com- 
pression of  the  framework,  through  an  exertion  of  muscular  power. 
The  lungs,  instead  of  being  freely  suspended  in  the  cavity  of  the 
chest,  as  in  Mammalia,  are  attached  to  the  ribs ;  and  their  own  tissue 
is  endowed  with  a  degree  of  elasticity,  which  causes  them  to  dilate 
when  they  are  permitted  to  do  so.  In  the  state  of  distension,  there- 
fore, which  is  natural  to  the  cavity  of  the  trunk,  the  lungs  are  ex- 
panded, and  fill  themselves  with  air,  which  they  draw  in  through  the 
trachea;  and  this  condition  they  retain,  until,  by  the  action  of  the 
external  muscles  upon  the  bony  framework,  the  cavity  of  the  trunk  is 
diminished,  and  the  air  is  expelled  from  the  lungs  and  air-sacs,  which 
are  again  filled  as  soon  as  the  pressure  is  taken  off. — As  the  air-sacs 
chiefly  communicate  with  the  part  of  the  lungs  that  is  most  distant 
from  the  trachea,  the  air  has  to  traverse  the  whole  extent  of  these  last 
organs,  both  when  it  is  being  drawn  into  the  air-sacs,  and  w^hen  it  is 
being  expelled  from  them  ;  so  that  it  is  made  to  serve  for  the  aeration 
of  the  blood  in  the  most  effectual  manner. 

674.  Thus,  although  the  respiratory  apparatus  of  Birds  does  not 
possess  the  highly-concentrated  development,  which  we  shall  find  it 
to  present  in  Mammals,  it  serves,  by  the  extension  of  the  aerating 
surface  through  the  body,  to  bring  the  air  and  the  blood  into  most 
intimate  relation ;  and  the  energy  of  the  function  is  further  provided 
for,  by  the  mode  in  which  the  pulmonary  circulation  is  carried  on  (a 
distinct  heart,  as  it  were,  being  provided  for  it,  §  564),  as  well  as  by 
the  arrangement  of  the  blood-vessels,  which  transmit  to  the  respira- 


1 


RESPIRATION  IN  BIRDS  AND  MAMMALS.  385 

tory  organs  the  whole  of  the  blood,  that  has  been  returned  in  a  car- 
bonated state  by  the  great  veins  of  the  system.  The  very  large  pro- 
portion of  red  corpuscles  contained  in  the  blood,  gives  additional 
effect  to  these  provisions.  The  very  high  amount  of  respiration  which 
is  natural  to  Birds,  and  which  cannot  be  suspended  even  for  a  short 
time  without  fatal  consequences,  has  a  direct  relation  (as  already 
explained)  with  their  extraordinary  muscular  activity ;  and  with  the 
high  bodily  temperature,  which  they  are  fitted  to  maintain,  and  which 
cannot  be  lowered  in  any  great  degree  without  the  suspension  of  their 
other  functions.  Birds  are  peculiarly  susceptible  of  impurities  in  the 
atmosphere;  and  it  has  been  shown  by  experiment,  that  if  a  Bird,  a 
Mammal,  and  a  Reptile,  be  placed  together  in  a  liaiited  quantity  of 
air,  which  gradually  becomes  vitiated  by  their  respiration,  the  Bird 
will  die  first,  the  Mammal  next,  and  the  Reptile  last.  Or  if  the  Bird 
be  placed  alone  in  a  limited  quantity  of  air,  and  be  left  until  the 
atmosphere  is  so  vitiated  as  to  be  no  longer  capable  of  supporting  its 
life,  a  Mammal  will  still  live  for  a  time  in  that  atmosphere  ;  and  when 
it  is  no  longer  fit  to  sustain  the  life  of  the  Mammal,  the  Reptile  may 
still  breathe  it  without  injury  for  a  considerable  period.  There  is 
strong  reason  to  believe,  indeed,  that  in  former  epochs  of  the  Earth's 
history,  when  the  Reptile  class  was  predominant,  supplying  the  place 
of  Mammals  on  land,  and  of  Birds  in  the  air,  the  atmosphere  was  so 
highly  charged  with  carbonic  acid,  as  not  to  be  capable  of  sustaining 
the  life  of  the  higher  air-breathing  Vertebrata. 

3.  Mechanism  of  Respiration  in  Mammalia  and  in  Man. 

675.  It  is  in  the  class  of  Mammalia,  that  we  find  the  Respiratory 
apparatus  presenting  its  highest  degree  of  concentration ;  and  the 
arrangements  for  its  action  the  most  complete.  The  lungs  are  divided 
into  cavities  of  extreme  minuteness ;  so  that  the  extent  of  surface 
which  they  expose  is  enormously  increased.  These  cavities,  or  air- 
cells  are  all  connected  with  the  trachea,  by  means  of  the  bronchial 
tubes  and  their  minute  subdivisions ;  but  on  account  of  the  minute- 
ness of  these  passages,  a  considerable  force  would  be  required  to 
inflate  the  air-cells  with  air,  if  their  distension  were  to  be  accom- 
plished by  the  propulsion  of  air  through  the  trachea,  as  we  have  seen 
to  be  the  normal  mode  of  inspiration  in  Reptiles.  Moreover,  if  the 
air  were  introduced  in  this  manner,  the  air-cells  would  be  the  last  por- 
tions of  the  pulmonary  structure  that.would  be  distended  by  it ;  as  well 
as  the  first  to  be  emptied,  when  the  air  is  forced  out  again  by  external 
pressure.  The  mechanism  of  Respiration  in  Mammalia,  however,  is 
so  arranged,  that  the  air  is  most  effectually  drawn  into  the  lungs;  in- 
stead of  being/orced  into  them;  and  the  distension  of  the  air-cells  is 
far  more  complete  than  it  could  be  rendered  in  the  latter  method, 
besides  being  accomplished  in  a  much  shorter  time. 

676.  The  general  principle  of  the  operation  is  this.  The  lungs  are 
suspended  in  a  cavity  that  is  completely  closed ;  being  bounded  above 

25 


386  MECHANISM  OF  RESPIRATION  IN  MAMMALS. 

and  around  by  the  bony  framework  of  the  thorax,  the  interspaces  of 
■which  are  filled  up  by  the  muscles  and  membranes ;  and  being  entirely 
cut  off  from  the  abdomen  below,  by  the  diaphragm.  Under  ordinary 
circumstances,  the  lungs  completely  fill  the  cavity;  their  external  sur- 
face, covered  by  the  pleura,  being  everywhere  in  contact  with  the 
pleural  lining  of  the  thorax.  But  the  capacity  of  the  thoracic  cavity 
is  susceptible  of  being  greatly  altered  by  the  movements  of  the  ribs, 
and  by  the  actions  of  the  diaphragm  and  abdominal  muscles  ;  as  will 
presently  be  explained  in  more  detail.  When  it  is  diminished,  the 
lungs  are  compressed,  and  a  portion  of  the  air  contained  in  them  is 
expelled  through  the  trachea.  On  the  other  hand,  when  it  is  increased 
the  elasticity  of  the  air  within  the  lungs  causes  them  immediately  to 
dilate,  so  as  to  fill  the  vacuum  that  would  otherwise  exist  in  the  tho- 
racic cavity;  and  a  rush  of  air  takes  place  down  the  air-tubes,  and 
into  the  remotest  air-cells,  to  equalize  the  density  of  the  air  they  in- 
clude (which  has  been  rarefied  by  the  dilatation  of  the  containing 
cavities)  with  that  of  the  surrounding  atmosphere. 

677.  The  diameter  of  the  ultimate  air-cells  of  the  Human  lung  varies 
from  about  the  l-200th  to  the  l-70th  of  an  inch.  Their  shape  is 
irregular ;  and  their  walls  are,  for  the  most  part,  flattened  against 
each  other.  Each  of  the  ultimate  ramifications  of  the  bronchial  tubes 
communicates  with  a  cluster  of  these    air-cells  grouped  around  it; 

those  which  are  in  immediate 
F'&^^2.  proximity  wuth  the  tube  open 

into  it  by  well-defined  circular 
apertures  ;  and  the  others  com- 
municate with  it  by  opening 
into  these  and  into  each  other. 
Each  air-cell  is  lined  by  an 
extension  of  the  mucous  mem- 
brane from  the  bronchial  tubes ; 
and  this  is  covered  by  a  deli- 
cate pavement-epithelium.  Be- 
tween the  adjacent  air-cells,  is 
a  network  of  fibrous  tissue, 
that  forms  the  connecting  me- 
dium by  which  they  are  held 
th^uuSrCg"!^  '^'  Capillaries  of  the  air-cells  of   together  ;  this  tissue  appears  to 

be  of  the  elastic  kind.  The 
pulmonary  arteries  subdivide  into  branches,  whose  ultimate  ramifica- 
tions form  an  extremely  minute  capillary  plexus;  and  this  is  disposed 
between  the  walls  of  the  adjacent  air-cells,  so  that  each  portion  of 
this  plexus  comes  into  relation  with  the  air  (through  the  lining  mem- 
brane of  the  contiguous  air-cells)  on  both  sides, — an  arrangement 
which  is  obviously  the  most  favourable  that  can  be  to  the  aeration  of 
the  contained  blood.  It  has  been  calculated  by  M.  Rochoux,  that 
the  number  of  air-cells  grouped  around  each  terminal  bronchus  is 
little  less  than  18,000;  and  that  the  total  number  in  the  lungs  amounts 


i 


I 


STRUCTURE  OF  THE  LUNGS  IN  MAN.  387 

lo  six  hundred  millions.  If  this  estimate  be  even  a  remote  approxi- 
mation to  the  truth,  it  is  evident  that  the  amount  of  surface  exposed 
by  the  walls  of  these  minute  cavities,  must  be  very  many  times  greater 
than  that  of  the  exterior  of  the  body. 

678.  The  larger  bronchial  tubes  are  more  or  less  cartilaginous;  but 
the  smaller  branches  do  not  possess  any  such  deposit  in  their  walls, 
though  still  retaining  their  circular  form.  We  find  in  the  latter  a 
fibrous  structure,  which  seems  to  possess  the  properties  of  non-striated 
muscle ;  and  by  this,  the  diameter  of  these  tubes  appears  to  be  gov- 
erned. The  contractility  of  the  walls  of  the  smaller  bronchi  may  be 
excited  by  chemical,  electrical,  or  mechanical  stimuli  applied  to 
themselves  ;  though  it  is  not  readily  caused  to  manifest  itself  by  sti- 
mulating the  nerves.  By  the  continued  influence  of  galvanism, 
bronchial  tubes  of  a  line  in  diameter  have  been  made  to  contract,  until 
their  cavity  was  nearly  obliterated.  What  purpose  this  contractility 
may  serve,  during  the  ordinary  actions  of  the  lungs,  it  is  not  easy  to 
say ;  but  it  manifests  itself  strongly  in  certain  diseased  conditions, 
especially  in  Spasmodic  Asthma,  which  appears  essentially  to  consist 
in  a  contracted  state  of  the  smaller  bronchial  passages,  occasioning 
an  interruption  to  the  passage  of  air  through  them.  It  is  interesting 
to  observe,  that  the  contractility  of  the  muscular  walls  of  these  tubes 
has  been  experimentally  found  to  be  greatly  diminished  by  the  appli- 
cation of  vegetable  narcotics,  especially  stramonium  and  belladonna, 
— substances  which  are  well  known  to  have  a  powerful  remedial  in- 
flueiTce  in  spasmodic  Asthma. 

679.  The  Lungs  themselves  appear  to  be,  almost  entirely,  passive 
instruments  of  the  Respiratory  function.  Their  contraction  when 
over-distended,  and  their  dilatation  after  extreme  pressure,  may  be 
partly  due  to  the  elasticity  of  their  structure  ;  which  seems  to  produce, 
when  acting  by  itself,  a  moderately  distended  state  of  the  air-cavities. 
This,  too,  is  the  condition  that  seems  most  natural  to  thecavity  of  the 
chest;  the  fullest  dilatation,  or  the  most  complete  contraction,  of 
which  it  is  capable,  being  only  accomplished  by  a  forcible  eflfort. 

680.  The  dilatation  of  the  cavity  of  the  chest,  which  constitutes 
Inspiration,  is  accomplished  by  two  sets  of  movements; — the  elevation 
of  the  ribs, — and  the  depression  of  the  diaphragm.  From  the  peculiar 
mode  in  which  the  ribs  are  articulated  w4th  the  spinal  column  at  one 
extremity,  and  from  the  angle  which  they  make  with  the  cartilages 
that  connect  them  to  the  sternum  at  the  other,  the  act  of  elevatioft 
tends  to  bring  the  ribs  and  the  cartilages  more  into  a  straight  line, 
and  to  carry  the  former  to  a  greater  distance  from  the  median  plane  of 
the  body,  whilst  the  sternum  is  also  thrown  forwards.  Consequently 
the  elevation  of  the  ribs  increases  the  capacity  of  the  thorax,  upw^ards, 
forwards,  and  laterally.  The  movement  is  chiefly  accomplished  by 
the  Scaleni  muscles,  which  draw  up  the  first  rib  ;  and  by  the  Inter- 
costals,  which  draw  the  other  ribs  into  nearer  proximity  with  each 
other,  so  that  the  total  amount  of  movement  in  each  rib  increases  as 
we  pass  from  above  downwards, — every  one  being  drawn  up  by  its 


388  MECHANISM  OF  RESPIRATION  IN  MAN. 

connection  with  the  one  above  it,  and  being  drawn  nearer  to  it  by  the 
action  of  its  own  intercostals.  The  elevation  of  the  ribs  is  further 
assisted  by  the  serratus  magnu§,  and  by  other  muscles  connected  with 
the  spine  and  the  scapula  ;  and  when  the  respiratory  movement  is  very 
forcibly  performed,  the  scapula  is  itself  drawn  upwards,  by  the  mus- 
cles that  descend  to  it  from  the  neck,  thus  producing  an  increased 
elevation  of  the  ribs,  and  an  unusual  enlargement  of  the  upper  part 
of  the  thoracic  cavity. — When  the  respiratory  action  is  to  be  per- 
formed, the  descent  of  the  ribs  is  occasioned  by  the  muscles  of  the 
spine  and  abdomen,  which  proceed  upwards  from  the  lower  part  of 
the  trunk ;  and  this  action  is  aided  by  the  elasticity  of  the  costal  car- 
tilages. 

681.  In  the  ordinary  act  of  inspiration,  however,  the  diaphragm 
performs  the  most  important  part.  The  contraction  of  this  muscle 
changes  its  upper  surface,  from  the  high  arch  that  it  forms  when  re- 
laxed and  pushed  upwards  by  .the  viscera  below,  to  a  much  more  level 
state  ;  though  it  never  approaches  very  closely  to  a  plane  ;  being 
somewhat  convex,  even  when  the  fullest  inspiration  has  been  taken. 
When  thus  drawn  down,  it  presses  upon  the  abdominal  viscera,  and 
causes  them  to  project  forwards,  which  they  are  allowed  to  do,  by 
the  relaxation  of  the  abdominal  muscles.  In  tranquil  breathing,  this 
action  is  alone  nearly  sufficient  to  produce  the  requisite  enlargement 
of  the  thoracic  cavity ;  the  position  of  the  ribs  being  very  little  altered. 
In  the  expiratory  movement,  the  diaphragm  is  altogether  passive  ; 
for,  being  in  a  state  of  relaxation,  it  is  forced  upwards  by  the  ab- 
dominal viscera,  which  are  pressed  inwards  by  the  contraction  of 
the  abdominal  muscles.  These  last,  therefore,  are  the  main  instru- 
ments of  the  expiratory  movement ;  diminishing  the  cavity  of  the  chest 
by  elevating  its  floor,  at  the  same  time  that  they  draw  its  bony  frame- 
work into  a  narrower  compass. 

682.  In  this  manner,  by  the  regularly  alternating  dilatation  and 
contraction  of  the  thoracic  cavity,  the  air  within  the  lungs  is  alter- 
nately increased  and  diminished  in  amount ;  and  thus  a  regular  ex- 
change is  secured.  This  exchange,  however,  can  only  affect  at  any 
one  time  a  certain  proportion  of  the  air  in  the  lungs;  thus  it  is  pro- 
bable, that  the  quantity  remaining  in  these  organs  after  ordinary  expi- 
ration is  above  100  cubic  inches,  whilst  the  amount  usually  expired 
is  not  above  20  cubic  inches.  Indeed  if  it  were  not  for  the  tendency 
of  gases  to  mutual  diffusion,  the  air  in  the  remote  air-cells  might 
never  be  renewed. — If  any  aperture  exist,  by  which  air  could  obtain 
direct  access  to  the  pleural  cavity,  the  lungs  would  not  be  dilated  by 
its  enlargement ;  for  the  vacuum  w^ould  be  supplied  much  more  rea- 
dily, by  the  direct  ingress  of  the  air  (provided  the  aperture  be  large 
enough),  than  by  the  distension  of  the  lung.  Thus  a  large  penetrat- 
ing wound  of  the  thoracic  cavity  may  completely  throw  out  of  use 
the  lung  of  that  side;  and  the  same  result  will  follow,  when  an  aper- 
ture forms  by  ulceration  in  the  substance  of  the  lung  itself,  establish- 
ing a  free  communication  between  the  pleural  cavity  and  one  of  the 


MECHANISM  OF  RESPIRATION  IN  MAN.  389 

bronchial  tubes  ;  so  that,  of  the  air  which  rushes  in  by  the  trachea,  to 
compensate  for  the  enlargement  of  the  thoracic  cavity,  a  great  part 
goes  at  once  into  that  cavity,  without  contributing  to  the  distension  of 
the  lungs,  and  therefore  without  serving  for  the  aeration  of  the  blood. 

683.  The  number  of  the  respiratory  movements  (that  is,  of  the  acts 
of  inspiration  and  expiration  taken  together)  may  be  probably  esti- 
mated at  from  14  to  18  per  minute,  in  a  state  of  health  and  of  repose 
of  body  and  mind.  Of  these,  the  greater  part  are  moderate  in  amount, 
involving  little  movement  except  in  the  diaphragm  ;  but  a  greater 
exertion,  attended  with  a  decided  elevation  of  the  ribs,  is  usually 
made  at  every  fifth  recurrence.  The  frequency  of  the  respiratory 
movements,  however,  is  liable  to  be  greatly  increased  by  various 
causes,  such  as  violent  muscular  exertion,  mental  emotion,  or  quick- 
ened circulation;  whilst  it  may  be  diminished  by  torpidity  of  the 
nervous  centres,  on  which  the  movement  depends, — as  we  see  in 
apoplexy,  narcotic  poisoning,  &c.  An  acceleration  seems  very  con- 
stantly to  take  place  in  diseases,  which  unfit  a  part  of  the  lung  for  the 
performance  of  its  function  ;  and  the  rate  bears  a  proportion  to  the 
amount  thus  thrown  out  of  use.  Thus,  the  usual  proportion  between 
the  respiratory  movements  and  the  pulse  being  as  1  to  4J  or  5,  it  may 
become  in  Pneumonia  as  1  to  3,  or  even  in  severe  cases  as  1  to  2  ;  the 
increase  in  the  number  of  respiratory  movements  being  much  greater 
in  proportion,  than  the  augmentation  of  the  rate  of  the  pulse.  But  it 
mus>t  be  remembered  by  the  practitioner,  that  a  simply  hysterical  state 
may  produce,  in  young  females,  an  extraordinary  acceleration  of  the 
respiration ;  the  number  of  movements  being  sometimes  no  less  than 
100  per  minute.  There  will  be  a  great  increase,  also,  in  the  number 
of  inspirations,  when  the  regular  movements  are  prevented  from  being 
fully  performed,  by  any  cause  that  aflfects  their  mechanism,  even  whilst 
the  lungs  themselves  are  quite  sound.  Thus  in  inflammation  of  the 
pleura  or  pericardium,  or  in  rheumatic  aflfections  of  the  intercostal 
muscles,  the  full  action  of  the  ribs  is  prevented  by  the  pain  which  the 
movements  produce  ;  and  the  same  is  the  case  in  regard  to  the  dia- 
phragm, when  the  peritoneum  or  the  abdominal  viscera  are  affected 
with  inflammation.  Under  such  circumstances,  there  is  an  involuntary 
tendency  to  make  up  for  the  deficiency  in  the  amount  of  the  respira- 
tory movements,  by  an  increase  in  their  number. 

684.  The  combined  actions  of  the  respiratory  muscles,  which  have 
been  now  explained,  belong  to  the  group  termed  reflex;  being  the 
result  of  the  operation  of  a  certain  part  of  the  nervous  centres,  which 
does  not  involve  the  will,  or  even  sensation,  and  which  may  continue 
when  all  the  other  parts  of  the  nervous  centres  have  been  removed. 
In  the  Invertebrated  Animals,  we  commonly  find  a  distinct  ganglionic 
centre  set  apart  for  the  performance  of  the  respiratory  movements ; 
and  the  division  of  the  nervous  centres  in  Vertebrated  animals,  which 
is  the  seat  of  the  same  function,  may  be  clearly  marked  out,  although 
it  is  not  so  isolated  from  the  rest.  It  is,  in  fact,  that  segment  of  the 
medulla  oblongata  and  upper  part  of  the  spinal  cord,  which  is  con- 


390  MECHANISM  OF  RESPIRATION  IN  MAN. 

nected  with  the  5th,  7th,  and  8th  pairs  of  cephalic  nerves,  and  with 
the  phrenic.  The  entire  brain  may  be  removed  from  above  (by  suc- 
cessive slicing),  and  the  whole  spinal  cord  may  be  destroyed  below ; 
and  yet  the  respiratory  movements  of  the  diaphragm  will  still  con- 
tinue,— those  of  the  intercostal  and  other  muscles  being  of  course 
suspended,  by  the  destruction  of  a  portion  of  the  cord,  from  which 
their  nerves  arise.  But  if  the  spinal  cord  be  divided,  between  the 
point  at  which  it  receives  the  5th  and  8th  pairs  of  nerves,  and  that 
at  which  it  gives  origin  to  the  phrenic,  the  movements  of  the  dia- 
phragm immediately  cease  ;  and  this  is  the  reason  why  death  is  so 
instantaneous,  in  cases  of  laxation  or  fracture  of  the  higher  cervical 
vertebrsB,  causing  pressure  upon  the  spinal  cord  just  below  its  exit 
from  the  cranium;  whilst  if  the  injury  take  place  below  the  origin 
of  the  phrenic  nerve,  life  may  be  prolonged  for  some  time. 

685.  The  Respiratory  movements,  like  other  reflex  actions  (§  394), 
depend  upon  a  stimulus  of  some  kind,  originating  at  the  extremities 
of  the  nerves,  propagated  towards  the  centre  by  the  afferent  trunks, 
and  giving  rise  to  a  motor  impulse,  which  is  transmitted  along  the 
efferent  or  motor  nerves  to  the  muscles,  and  which  occasions  their 
contraction.  Now  the  importance  of  the  respiratory  function  to  the 
maintenance  of  life,  which  has  already  been  sufficiently  pointed  out, 
necessitates  an  ample  provision  for  its  due  performance;  and  thus  we 
find  thatthe  stimulus  for  theexcitementof  the  movements  may  be  trans- 
mitted through  several  channels.  Its  chief  source,  no  doubt,  is  in  the 
lungs ;  and  arises  from  the  presence  of  venous  blood  in  the  capillaries 
and  of  carbonic  acid  in  the  air-cells.  Under  ordinary  circumstances, 
— that  is,  when  the  blood  is  being  duly  aerated,  and  the  air  being 
properly  renewed, — the  impression  thus  made  upon  the  nerves  of  the 
lungs,  is  so  faint,  that  we  cannot  perceive  it,  even  when  we  specially 
direct  our  attention  to  it.  But  if  we  suspend  the  movements  for  a 
moment  or  two,  we  immediately  experience  a  sensible  uneasiness. 
The  ParVagum  is  obviously  the  channel,  through  which  this  impres- 
sion is  conveyed  to  the  nervous  centres ;  and  it  is  found  that,  if  the 
trunk  of  this  nerve  be  divided  on  both  sides,  the  respiratory  move- 
ments are  greatly  diminished  in  frequency.  Hence  it  is  undoubtedly 
one  of  the  principal  excitors  of  the  respiratory  movements. 

686.  But  the  sensory  nerves  of  the  general  surface,  and  more  par- 
ticularly the  sensory  portion  of  the  Fifth  pair,  which  supplies  the  face, 
are  most  important  auxiliaries,  as  excitor  nerves ;  the  inspiratory 
movement  being  peculiarly  and  forcibly  excited  by  impressions  made 
upon  them,  especially  by  the  contact  of  cold  air  or  water  with  the 
face.  The  power  of  the  impression  made  by  the  air  upon  the  gene- 
ral surface,  and  particularly  upon  the  face,  in  exciting  the  inspiratory 
movement,  is  well  seen  in  the  case  of  the  first  inspiration  of  the  new- 
born infant,  which  appears  to  be  excited  solely  in  this  manner.  An 
inspiratory  effort  is  often  made,  as  soon  as  the  face  has  emerged  from 
the  Vagina  of  the  mother ;  whilst,  on  the  other  hand,  if  the  face  be 
prevented  from  coming  into  contact  with  cool  air,  the  inspiratory 


i 


REFLEX  CHARACTERS  OF  RESPIRATORY  MOVEMENTS.        391 

effort  may  be  wanting.  When  it  does  not  duly  take  place,  it  may 
often  be  excited  by  a  slap  with  the  flat  of  the  hand  upon  the  nates 
or  abdomen  ;  a  fact  which  shows  the  special  influence  of  impres- 
sions upon  the  general  surface,  in  rousing  the  motor  impulse  in  the 
medulla  oblongata,  and  in  causing  its  transmission  to  the  muscles. 
The  deep  inspirations  which  follow  a  dash  of  cold  water  upon  the 
face,  or  the  descent  of  the  cold  douche  or  of  the  divided  streams  of  the 
shower-bath  upon  the  body,  or  the  shock  of  immersion  in  the  cold 
plunge-bath,  all  testify  to  the  powerful  influence  of  such  impressions 
in  the  adult;  and  the  efficacy  of  other  kinds  of  irritation  of  the  skin, 
such  as  beating  with  holly  twigs,  in  maintaining  the  respiratory  move- 
ments in  cases  of  narcotic  poisoning,  shows  that  the  required  impres- 
sions are  not  restricted  to  the  contact  of  cold  air  or  water.  It  seems 
probable,  from  various  facts,  that  the  presence  of  venous  blood  in  the 
arterial  capillaries  of  the  system,  and  the  consequent  stagnation  in  the 
current  through  them  (§  597),  may  exert  an  influence  through  the 
Sympathetic  system :  which  may  be  transmitted,  by  the  copious  inos- 
culations of  that  system  with  the  Par  Vagum,  to  the  Medulla  Ob- 
longata ;  and  which  may  there  serve  as  a  valuable  auxiliary  in  excit- 
ing the  respiratory  movements. 

687.  Of  the  mode  in  which  the  impressions,  thus  transmitted  to 
the  Medulla  Oblongata,  act  in  exciting  the  motor  impulses  which 
issue  from  it,  nothing  is  known ;  but  these  impulses,  directed  along 
the  phrenic,  intercostal,  and  other  nerves,  produce  the  requisite  move- 
ments. When  the  stimulus  is  unusually  strong,  various  nerves  and 
muscles  are  put  in  action,  which  do  not  co-operate  in  the  ordinary 
movements  of  inspiration ;  and  it  may  sometimes  be  observed,  that 
movements  are  thus  excited  in  parts,  which  will  not  act  in  obedience 
to  the  will,  being  to  all  appearance  completely  paralyzed.  This  fact 
shows  how  completely  the  class  of  actions  in  question  is  independent 
of  the  influence  of  the  mind  ;  but  we  must  not  lose  sight  of  the  con- 
trol which  the  mind,  especially  in  the  higher  classes  of  animals,  pos- 
sesses over  them.  Various  actions  of  the  respiratory  muscles,  par- 
ticularly those  of  weeping  and  laughing,  are  the  most  direct  means  of 
expressing  the  passions  and  emotions  of  the  mind  ;  and  are  invo- 
luntarily excited  by  these.  And,  again,  the  respiratory  actions  are 
placed  to  a  certain  degree  under  the  control  of  the  will ;  in  order 
that  they  may  be  subservient  to  the  production  of  vocal  sounds,  and 
to  the  actions  of  speech,  singing,  &c.  The  will  cannot  long  suspend 
the  respiratory  movements ;  for  the  stimulus  to  their  involuntary  per- 
formance soon  becomes  too  powerful  to  be  any  longer  resisted.  And 
it  is  well  that  it  should  be  so  ;  for  if  the  performance  of  this  most  im- 
portant function  were  left  to  our  own  choice,  a  few  moments  of  for- 
getfulness  would  be  productive  of  fatal  results.  But  it  is  to  the  power 
which  the  will  possesses,  of  directing  and  controlling  the  respiratory 
movements,  that  we  owe  the  faculty  of  producing  articulate  sounds, 
and  thus  of  holding  the  most  direct  and  intimate  converse  with 
each  other. 


392      INTERCHANGE  OF  OXYGEN  AND  CARBONIC  ACID. 

688.  It  is  essential  for  the  due  performance  of  the  respiratory  move- 
ments, that  the  portion  of  the  nervous  centres,  on  which  they  depend, 
should  be  in  a  state  of  activity.  This  is  the  case,  under  ordinary 
circumstances,  throughout  life.  The  state  of  perfect  quiescence,  to 
which  the  brain  is  liable,  never  affects  the  medulla  oblongata ;  and 
the  respiratory  movements  are  consequently  kept  up  with  as  much 
regularity  and  energy  (in  proportion  to  the  requirements  of  the  sys- 
tem), during  our  sleeping,  as  during  our  waking  hours.  But  if  any 
cause  induce  torpidity  of  the  medulla  oblongata,  the  respiratory  move- 
ments are  then  retarded,  or  even  suspended  altogether ;  and  all  the 
consequences  of  the  cessation  of  the  [aeration  of  the  blood  speedily 
develop  themselves  (§  706).  This  is  seen  in  apoplexy;  when  the 
pressure,  or  other  cause  of  suspended  activity,  which  at  first  affected 
the  brain  alone,  gradually  propagates  its  influence  downwards.  The 
same  is  the  case  in  narcotic  poisoning ;  in  which  also  the  brain  is  the 
first  to  be  affected,  and  may  suff*er  alone ;  but  if  the  noxious  influence 
be  propagated  to  the  medulla  oblongata,  it  manifests  itself  in  the  re- 
tardation of  the  respiratory  movements,  and,  when  sufficiently  power- 
ful, in  their  complete  suspension.  Under  such  circumstances,  it  is 
requisite  to  resort  to  all  possible  means  of  keeping  up  the  respiratory 
movements  ;  and  when  these  fail,  artificial  respiration  may  be  suc- 
cessfully employed.  For  if,  by  such  means,  the  circulation  can  be 
prevented  from  failing  for  a  sufficient  length  of  time,  the  ordinary  pro- 
cesses of  nutrition  go  on,  the  poisonous  matter  is  gradually  decom- 
posed or  eliminated  by  the  secreting  organs  ;  and  the  nervous  centres 
resume  their  usual  functions.  A  torpid  condition  of  the  medulla 
oblongata,  inducing  a  retardation  of  the  respiratory  movements,  seems 
to  be  one  of  the  morbid  conditions  attendant  upon  typhoid  fever ;  and 
probably  depends  in  the  first  instance  upon  a  disordered  state  of  the 
blood,  which  does  not  exert  its  usual  vivifying  influence.  In  such 
cases,  the  proportion  of  the  respiratory  movements  to  the  pulse  sinks 
as  low  as  1  to  6,  or  even  as  1  to  8 ;  and  thus  the  due  aeration  of  the 
blood  is  not  performed,  and  its  stimulating  properties  are  still  further 
diminished. 

4.   Chemical  Phenomena  of  Respiration, 

689.  Having  now  fully  considered  the  means,  by  which  the  Atmo- 
sphere and  the  blood  are  brought  into  relation  in  the  lungs,  we  have 
to  examine  into  the  results  of  their  mutual  action.  It  will  be  remem- 
bered that  the  Atmosphere  contains  about  21  per  cent,  of  Oxygen  to 
79  of  Nitrogen,  by  measure  ;  or  23  parts  of  Oxygen  to  77  of  Nitro- 
gen, by  weight.  The  Nitrogen  seems  to  perform  no  other  part  than 
that  of  diluting  the  oxygen ;  at  least  the  results  of  the  most  recent  and 
exact  experiments  render  it  very  doubtful,  whether  (in  the  respiration 
of  Man  at  least)  any  change  is  effected  in  the  nitrogen  of  the  inspired 
air.  The  leading  phenomenon  of  respiration,  is  the  removal  of  a  cer- 
tain quantity  of  Oxygen  from  the  air,  and  its  replacement  by  Carbonic 


AMOUNT  OF  CARBONIC  ACID  EXHALED.  393 

acid.  The  relative  proportions,  which  the  oxygen  absorbed,  and  the 
carbonic  acid  exhaled,  bear  to  one  another,  have  been  variously 
stated.  The  most  recent  and  trustworthy  experiments  on  this  subject 
(those  of  Brunner  and  Valentin)  lead  to  a  very  interesting  result. 
According  to  the  law  of  the  "  mutual  diffusion"  of  gases,  the  volumes 
of  any  two  gases,  that  pass  through  a  porous  medium  to  mingle  with 
each  other,  will  be  respectively  in  the  inverse  proportion  to  the  square 
roots  of  their  specific  gravities.  Now  when  oxygen  is  on  the  outer 
side,  and  carbonic  acid  on  the  inner,  the  volume  of  oxygen  that 
passes  inwards  will  exceed  that  of  the  carbonic  acid  that  passes  out- 
wards ;  and  this  in  the  proportion  of  1174  to  1000.  This  calculation, 
deduced  from  the  relative  densities  of  the  two  gases,  corresponds  so 
closely  with  the  actual  result  of  experiments  upon  the  respiration  of 
Man,  that  it  seems  next  to  certain,  that  the  interchange  of  oxygen  and 
carbonic  acid,  which  occurs  between  the  air  and  the  blood  in  the 
lungs,  takes  place  in  exact  accordance  with  this  law  of  mutual  dif- 
fusion. 

690.  Now  Carbonic  Acid  contains  precisely  its  own  volume  of 
oxygen ;  consequently,  of  the  1174  parts  of  oxygen  absorbed,  1000 
are  excreted  again  by  the  lungs  in  the  form  of  carbonic  acid  ;  and 
there  remain  174,  or  nearly  15  per  cent.,  to  be  accounted  for  in  other 
ways.  It  is  certain  that  some  of  this  enters  into  combination  with  the 
sulphur  and  phosphorus  of  the  original  components  of  the  body ;  and 
converts  these  into  sulphuric  and  phosphoric  acids  ;  and  the  remainder 
must  enter  into  other  chemical  combinations,  very  probably  uniting 
with  the  hydrogen  of  the  fatty  matter,  to  form  part  of  the  water 
which  is  exhaled  from  the  lungs. 

691.  It  is  difficult  to  form  an  exact  estimate  of  the  actual  quantity 
of  Carbon,  thrown  off  from  the  lungs  in  the  form  of  Carbonic  Acid 
during  any  lengthened  period  ;  since  the  amount  disengaged  during 
experiments  carried  on  for  a  limited  time,  cannot,  for  many  reasons, 
be  taken  as  affording  a  fair  average.  Thus  the  quantity  will  vary  with 
the  external  temperature,  with  the  state  of  previous  rest  or  activity, 
with  the  length  of  time  that  has  elapsed  since  a  meal,  and  particularly 
with  the  general  development  of  the  body.  The  amount  of  carbonic 
acid  exhaled  is  greatly  increased  by  external  cold  ;  as  is  shown  in 
the  results  of  such  experiments  as  the  following.  Small  Birds  and 
Mammals  having  been  enclosed  in  a  limited  quantity  of  air,  for  the 
space  of  an  hour,  at  ordinary  temperatures,  the  quantity  of  carbonic 
acid  they  produced  was  noted.  The  experiment  was  then  repeated. at 
a  temperature  nearly  approaching  that  of  the  body  ;  and  was  performed 
a  third  time  at  a  temperature  of  about  32°.  The  following  are  the 
comparative  amounts. 


Temp.  590^680. 

Temp  860—1060. 

Temp,  about  320. 

Grammes. 

Grammes. 

Grammes. 

A  Canary 

0-250 

0-129 

0-325 

A  Turtle-dove 

0-684 

0-366 

0-974 

Two  Mice 

0-498 

0-268 

0-531 

A  Guinea-pig 

2-080 

1-453 

3006 

394  AMOUNT  OF  CARBONIC  ACID  EXHALED. 

Thus  it  would  appear  that  the  quantity  of  carbonic  acid  exhaled  be- 
tween 86°  and  106°  is  not  much  more  than  half  of  that  which  is 
exhaled  between  59°  and  68° ;  and  is  only  about  two-fifths  of  that 
which  is  given  off  at  32°. 

692.  The  quantity  of  carbonic  acid  exhaled  during  exercise,  and 
for  a  certain  time  after  it,  and  also  after  a  full  meal,  is  considerably 
increased  ;  whilst  on  the  other  hand,  it  is  greatly  diminished  during 
sleep.  Thus  a  person  who  was  excreting  145  grains  of  carbon  per 
hour,  whilst  fasting  and  at  rest,  excreted  165  after  dinner,  and  190 
after  breakfast  and  a  walk ;  whilst  he  only  excreted  100  during  sleep. 
The  variation  with  the  general  development  of  the  body,  and  also 
with  the  sex  and  age,  is  considerable.  Thus,  the  exhalation  is  almost 
always  greater  in  males  than  in  females  of  the  same  age,  at  every 
period  of  life  except  childhood.  In  males,  the  quantity  increases 
regularly  from  eight  to  thirty  years  of  age,  remaining  nearly  stationary 
until  forty ; — thus  it  averages  77*5  grains  of  carbon  per  hour  at  eight 
years  ;  135  grains  at  fifteen  ;  176*7  grains  at  twenty  ;  and  189  grains 
between  thirty  and  forty.  Between  forty  and  fifty,  there  is  a  well- 
marked  diminution,  the  average  being  then  156  grains  ;  and  the  dimi- 
nution continues  up  to  extreme  old  age,  when  the  amount  exhaled 
scarcely  exceeds  that  which  is  extricated  at  ten  years  of  age  ;  thus, 
between  sixty  and  eighty,  it  was  142*5  grains;  and  in  a  man  of  a 
hundred  and  two,  it  was  only  91*5  grains.  These  average  results, 
however,  are  widely  departed  from  in  individual  cases  ;  an  extraor- 
dinary development  of  the  muscular  system  being  always  accompanied 
by  a  high  rate  of  extrication  of  carbon  ;  and  vice  versa.  Thus  a  man 
of  remarkable  muscular  vigour,  whose  age  was  twenty-six  years, 
exhaled  217  grains  of  carbon  in  an  hour ;  a  robust  man  of  sixty  ex- 
haled 209*4  grains ;  and  an  old  man  of  ninety-two,  who  in  his 
younger  days  had  possessed  uncommon  muscular  powers,  and  who 
preserved  a  remarkable  degree  of  energy,  still  consumed  at  the  rate 
of  151  grains  per  hour.  On  the  other  hand,  a  man  of  slight  muscular 
development,  at  the  age  of  forty-five,  only  exhaled  132  grains;  and 
another  at  the  age  of  seventy-six,  only  92*4  grains. 

693.  Infemales,  nearly  the  same  proportional  increase  goes  on,  up 
to  the  time  of  puberty  ;  when  the  quantity  abruptly  ceases  to  increase, 
and  remains  stationary  so  long  as  menstruation  continues  regular.  The 
average  quantity  of  carbonic  acid  exhaled  by  girls  nearly  approaching 
puberty,  is  about  100  grains  per  hour  ;  and  it  remains  at  this  standard 
until  nearly  the  close  of  menstrual  life.  At  the  period  of  the  cessation 
of  the  catamenia,  it  undergoes  a  perceptible  increase;  the  average, 
between  forty  and  fifty  years  of  age,  being  about  130  grains  per  hour ; 
and  the  quantity  exhaled  in  a  woman  of  great  muscular  development, 
and  of  forty- four  years  of  age,  rising  to  152*4  grains  in  an  hour.  After 
the  age  of  fifty,  or  thereabouts,  the  quantity  decreases,  as  in  men.  It 
is  remarkable  that,  during  pregnancy,  there  is  the  same  increase  in  the 
exhalation  of  carbon,  as  there  is  after  the  final  cessation  of  the  cata- 


AMOUNT  OF  CARBONIC  ACID  EXHALED.  395 

menia  ;  and  the  same  takes  place,  if  the  menstrual  discharge  be  tem- 
porarily suspended,  through  any  other  cause. 

694.  It  is  obviously  difficult,  then,  to  obtain  exact  estimates,  from 
any  experiments  conducted  for  a  short  time  only,  of  the  total  amount 
of  carbon  thrown  off*  during  a  lengthened  period  ;  since  the  condition 
of  the  individual  varies  so  greatly  at  different  times  ;  and  the  variation 
amongst  different  individuals  is  so  great.  Moreover,  of  the  total 
amount  of  carbon  excreted  in  a  gaseous  form,  a  certain  part  is  un- 
doubtedly set  free  from  the  skin ;  and  the  proportion  of  this  has  not 
been  yet  determined.  As  a  means  of  measuring  the  whole  quantity  of 
carbonic  acid  set  free,  without  causing  the  respiratory  movements  to 
be  performed  in  any  unnatural  manner.  Prof.  Scharing  constructed  an 
air-tight  chamber,  of  dimensions  sufficient  to  allow  an  individual  to 
remain  in  it  for  some  time  without  inconvenience  ;  and  so  arranged, 
that  he  could  eat  and  drink,  read,  or  sleep,  within  it.  This  was  con- 
nected with  an  apparatus,  by  which  the  air  was  continually  renewed; 
and  the  air  drawn  oflf  was  carefully  analyzed  in  order  to  determine  the 
quantity  of  carbonic  acid  contained  in  it.  The  average  per  hour,  in 
different  states,  having  been  ascertained,  it  was  calculated  that,  allow- 
ing seven  hours  for  sleep  in  adults,  and  nine  hours  for  children,  the 
total  amount  of  carbon  consumed  in  the  twenty-four  hours  was  as 
follows : — 

No.  Weighing.  Grains.  Oz.  Troy. 

1.  A  male,  aged  thirty-five,  131    lbs. 

2.  A  male,  aged  sixteen,  115J  lbs. 

3.  A  soldier,  aged  twenty-eight,  164    lbs. 

4.  A  girl,  aged  nineteen.  111    lbs. 

5.  A  boy,  aged  nearly  ten,  44    lbs. 

6.  A  girl,  aged  ten,  46    lbs. 

695.  This  estimate  is  perhaps  rather  too  low ;  as  it  does  not  take 
sufficient  account  of  the  great  increase,  which  is  produced  by  exercise. 
Another  method  has  been  adopted  by  Prof.  Liebig;  who  endeavoured 
to  ascertain  the  total  amount  of  carbon  excreted  from  the  body  in  the 
form  of  carbonic  acid,  by  comparing  the  amount  of  carbon  taken  in 
as  food,  with  that  contained  in  the  feces  and  urine ;  the  difference  being 
set  down  to  the  account  of  respiration.  His  estimate  amounts  to  the 
very  large  sum  of  13*9  oz.  of  solid  carbon  per  day,  which  he  consi- 
ders to  be  thus  set  free  by  the  lungs  and  skin ;  but  this  is  almost  cer- 
tainly above  the  truth.  The  observations  were  made  upon  a  body  of 
soldiers  who  were  subjected  to  severe  daily  exertion ;  and  they  were 
far  from  being  exactly  conducted,  many  of  the  items  being  set  down 
by  guess  only,  whilst  of  others  no  account  whatever  was  taken.  We 
may  perhaps  consider  10  or  11  oz.  as  more  nearly  representing  the 
amount  of  carbon  consumed  by  adult  men  exposed  to  severe  exer- 
tion ;  whilst  from  Prof.  Scharling's  experiments  it  may  be  inferred, 
that  from  7  to  8  oz.  of  carbon  are  thrown  off*  during  the  twenty-four 
hours  by  the  lungs  and  skin  of  adult  men  not  using  much  active  exer- 


3380 

or 

7-0 

3450 

or 

7-2 

3692 

or 

7-7 

2555 

or 

5-3 

2050 

or 

4-3 

1938 

or 

4-0 

396  AMOUNT  OF  CARBONIC  ACID  EXHALED. 

tion  ;  to  which  another  ounce  or  two  may  be  added,  as  the  increased 
quantity  excreted  during  moderate  exercise. — On  the  other  hand,  from 
experiments  made  upon  the  quantity  of  carbonic  acid  exhaled  from 
the  lungs  alone  during  a  given  time,  it  would  appear  that  the  pul- 
monary excretion  of  carbon  amounts  to  between  b\  and  8  oz.  in  the 
twenty-four  hours ;  and  the  difference  may  be  partly  set  down  to  the 
account  of  the  cutaneous  respiration. 

696.  If  we  assume  10  oz.  or  4800  grains  of  solid  carbon  as  the  total 
amount  excreted  from  the  lungs  and  skin  of  a  male  adult,  using  active 
exercise  in  the  course  of  twenty-four  hours,  w^e  find  that  the  volume 
of  carbonic  acid  thus  generated  must  be  nearly  37,000  cubic  inches,  or 
more  than  21  cubic  feet.  Of  this  about  16  cubic  feet  are  probably 
extricated  from  the  lungs.  But  it  is  probable  that  about  10  cubic  feet 
per  day  is  near  the  ordinary  average.  Now  it  has  been  ascertained, 
that  the  whole  quantity  of  air  which  passes  through  the  chest  during 
that  time  under  similar  circumstances,  is  about  2QQ  cubic  feet;  so  that 
the  proportion  of  carbonic  acid  contained  in  the  expired  air  seems  to 
average  about  4  per  cent.  It  is  certain,  however,  that  this  proportion 
may  rise  much  higher ;  particularly  when  the  respiratory  movements 
are  slowly  and  laboriously  performed.  Now  in  order  that  the  blood 
should  be  properly  aerated,  it  is  requisite  that  the  air  should  contain 
no  previous  impregnation  of  carbonic  acid  ;  since  the  diffusion  of  even 
a  moderate  per  centage  of  that  gas  through  the  inspired  air,  seriously 
impedes  the  exhalation  of  more.  Thus  it  was  found  by  Messrs.  Allen 
&  Pepys,  that  when  300  cubic  inches  of  air  were  respired  for  three 
minutes,  only  28J  inches  of  carbonic  acid  (or  somewhat  more  than  9 
per  cent.)  were  present  in  it;  though  the  rate  of  its  production  in  a 
parallel  experiment,  in  which  fresh  air  was  taken  in  at  each  inspira- 
tion, w^as  32  cubic  inches  per  minute,  or  96  cubic  inches  in  three 
minutes.  That  it  is  not  the  deficiency  of  oxygen,  but  the  presence  of 
carbonic  acid  in  the  inspired  air,  which  impedes  the  free  aeration  of 
the  blood,  is  proved  by  the  recent  experiments  of  Dr.  D.  B.  Reid  ; 
who  has  shown  that  an  animal  maybe  kept  alive  in  a  limited  quantity 
of  air,  until  nearly  all  its  oxygen  is  exhausted,  if  an  eff*ectual  provi- 
sion be  made  for  drawing  off'the  carbonic  acid  as  fast  as  it  is  generated. 

697.  An  animal  thus  made  to  breathe  an  atmosphere,  \diich  con- 
tains less  than  its  normal  proportion  of  oxygen,  resembles  one  which 
is  made  to  breathe  a  rarefied  atmosphere,  such  as  that  which  exists  on 
the  summits  of  high  mountains.  All  persons  who  have  made  such 
ascents,  have  experienced  the  insufficiency  of  rarefied  air  to  sustain 
the  degree  of  respiration  required  for  active  exertion.  As  long  as  the 
body  remains  at  rest,  no  inconvenience  is  perceived ;  but  as  soon  as 
the  muscular  system  is  put  into  action,  the  insufficiency  of  the  supply 
of  oxygen  is  manifested  by  the  feeling  of  distress  and  languor  ;  which 
becomes  so  severe,  that  the  individual,  if  unused  to  such  ascents,  is 
obliged  to  stop  and  take  breath  at  every  few  steps.  The  necessity 
for  doing  so  will  be  easily  understood,  when  it  is  remembered  that 
when  the  pressure  of  the  atmosphere  is  reduced  to  half  its  usual 


CHANGES  EFFECTED  IN  THE  BLOOD.  397 

amonnt,  the  hulk  of  a  given  weight  of  air  will  be  twice  as  great  as  at 
the  surface  of  the  earth,  or  the  same  measure  will  weigh  only  half  as 
much.  Consequently,  when  the  chest  is  completely  filled  with  air, 
the  real  quantity  of  oxygen  included  in  it,  is  only  half  of  that,  which 
is  drawn  in  by  a  corresponding  inspiration  at  the  earth's  surface. 

698.  Although  an  impregnation  of  carbonic  acid,  to  the  amount  of 
seven  or  eight  per  cent.,  would  be  required  to  destroy  life  in  most 
warm-blooded  animals,  yet  a  much  smaller  proportion  is  sufficient  to 
produce  very  injurious  results.  Thus  the  discomforts  occasioned  by 
the  presence  of  a  crowded  audience  in  a  church,  lecture-room,  or 
theatre,  w^hich  is  not  provided  with  sufficient  ventilation,  are  due  in 
great  part  to  the  continued  respiration  of  air,  which  becomes  loaded 
in  the  course  of  an  hour  or  two  with  carbonic  acid  gas,  to  the  amount 
of  from  one-half  to  two  per  cent., — as  has  been  ascertained  both  by 
direct  experiment,  and  by  calculation.  And  there  can  be  little  doubt, 
that  the  habitual  respiration  of  such  air,  in  the  narrow  and  noisome 
dwellings  of  the  poor,  or  in  crowded  factories  and  workshops,  has  a 
tendency  to  produce,  both  directly  and  indirectly,  much  loss  of  phy- 
sical and  mental  vigour,  and  also  to  blunt  the  acuteness  of  the  moral 
feelings. 

699.  Having  thus  considered  the  changes  produced  by  the  Respi- 
ratory function,  in  the  air  submitted  to  it,  we  have  next  to  inquire 
into  converse  series  of  change  effected  by  it  in  the  blood.  The  nature 
of  these  cannot  be  well  stated  with  precision ;  as  they  have  not  yet 
been  fully  determined.  It  was  formerly  supposed,  that  the  venous 
blood  arrives  at  the  lungs  charged  with  carbon;  and  that  this  carbon 
is  united  with  the  oxygen  of  the  air,  in  the  lungs  themselves.  Nu- 
merous facts,  however,  go  to  prove,  that  the  blood  comes  to  the  lungs 
charged  with  carbonic  acid;  and  that  it  gives  out  this  ready  formed, 
and  receives  oxygen  in  its  stead.  Thus  it  has  been  already  shown, 
that  there  is  a  positive  disappearance  of  oxygen  ;  more  of  that  element 
being  withdrawn  from  the  atmosphere,  than  is  restored  to  it  in  the 
condition  of  carbonic  acid ;  so  that  we  know  that  the  surplus  must 
be  received  into  the  blood.  Moreover,  the  quantity  of  oxygen  ab- 
sorbed exactly  replaces  the  quantity  of  carbonic  acid  set  free,  accord- 
ing to  the  law  of  "  mutual  diffusion;"  which  could  scarcely  be  the 
case,  unless  the  latter  were  contained  in  the  blood  already  formed. 
Further,  cold-blooded  animals  may  be  made  to  breathe  nitrogen  or 
hydrogen  for  a  sufficient  length  of  time,  to  cause  a  large  quantity  of 
carbonic  acid  to  be  disengaged;  and  this  must  have  been  brought  to 
the  lungs  ready  formed,  since  no  oxygen  was  present  there  to  gene- 
rate it.  Lastly,  it  can  be  shown  by  experiment,  that  oxygen,  carbo- 
nic acid,  and  nitrogen  exist  in  a  free  state  in  blood,  arterial  as  well 
as  venous ;  but  that  the  proportion  of  oxygen  is  greater  in  arterial  than 
in  venous  blood,  whilst  that  of  carbonic  acid  is  less.  The  following 
table  expresses  the  per  centage  of  each  kind  of  gas  in  the  two  sorts 
of  blood  respectively ;  as  deduced  from  the  experiments  of  Magnus. 


Arterial  Blood. 

Venous  Blood 

62-3 

71-6 

23-2 

15-3 

14-5 

131 

398  EXHALATION  OF  WATER  FROM  THE  LUNGS. 


Carbonic  acid     . 

Oxygen      .... 

Nitrogen    .... 

Thus  it  appears  that  the  quantity  of  nitrogen  is  very  nearly  the  same 
in  both,  as  would  be  anticipated  from  what  has  been  already  stated  in 
regard  to  its  non-participation  in  the  respiratory  process;  whilst  about 
one-third  of  the  free  oxygen  of  arterial  blood  disappears  during  its  cir- 
culation in  the  systemic  capillaries,  to  be  replaced  by  an  equivalent 
amount  of  carbonic  acid  ;  and  a  converse  change  takes  place  in  the 
pulmonary  capillaries,  this  additional  portion  of  free  carbonic  acid 
being  set  free,  and  replaced  by  oxygen. 

700.  Thus  it  is  evident,  that  a  part  of  the  change  effected  in  the 
blood  consists  in  an  alteration  in  the  proportion  of  the  gases  which 
always  exist  in  it,  either  entirely  free,  or  in  a  state  of  such  loose  com- 
bination that  they  can  be  removed  by  the  air-pump.  But  it  cannot 
be  doubted,  that  a  portion  of  the  effect  consists  in  the  oxidation  of  the 
proteine  of  the  fibrinous  constituent ;  since  the  fibrin  of  arterial  blood 
possesses  properties  that  distinguish  it  from  that  of  venous.  And  it 
seems  probable,  also,  for  the  reasons  formerly  stated,  that  the  hemato- 
sine  of  the  red  corpuscles  undergoes  a  change  under  the  influence  of  ^ 
oxygen  in  the  lungs,  and  a  converse  change  in  the  systemic  capillaries, 
where  it  is  subjected  to  the  influence  of  carbonic  acid.  This  much 
appears  tolerably  certain : — that  a  part  of  the  oxygen  imbibed  in  the 
lungs,  is  appropriated  to  the  oxidation  of  the  matters  set  free  by  the 
decomposition  of  the  solid  tissues; — whilst  another  part  enters  into 
combination  with  fatty,  saccharine,  or  farinaceous  matters,  existing  in 
the  blood  itself,  and  destined  to  be  carried  oflfin  the  form  of  carbonic 
acid  and  water,  without  ever  entering  into  the  composition  of  the  solid 
fabric.  The  relative  amounts  of  carbonic  acid  formed  in  these  two 
modes,  vary  in  different  animals,  and  in  diff*erent  states  of  the  same 
individual ;  for  a  man  in  a  warm  atmosphere,  taking  a  moderate 
amount  of  exercise,  may  thus  set  free,  by  the  waste  of  his  muscular 
and  other  tissues,  a  sufficient  quantity  of  carbon,  for  the  maintenance 
of  his  animal  heat  by  its  union  with  oxygen ;  but  this  is  far  from 
being  sufficient,  when  a  larger  amount  of  heat  must  be  evolved,  to 
sustain  the  temperature  of  the  body  in  a  colder  climate. 

701.  The  blood  parts  in  the  lungs  with  a  very  large  amount  of 
moisture;  for  the  inspired  air  is  always  saturated  with  fluid,  as  soon 
as  it  reaches  the  air-cells ;  and,  as  it  is  heated  at  the  same  time  to 
about  98°,  it  thus  receives  a  considerable  addition,  even  if  it  were 
previously  charged  with  as  much  as  it  could  contain  at  a  lower  tempe- 
rature. The  total  quantity  of  fluid  thus  disengaged  will  vary,  there- 
fore, with  the  amount  previously  contained  in  the  atmosphere ;  being 
greater  as  this  was  less,  and  vice  versa ;  the  expired  air  being  always 
charged  with  as  much  as  it  can  contain  at  the  temperature  of  98°  or 
99°.     It  cannot  be  doubted,  that  a  great  part  of  this  water  is  a  simple 


EXHALATION  OF  WATER  FROM  THE  LUNGS.— ASPHYXIA.      399 

exhalation  of  that  which  has  been  absorbed  ;  but,  on  the  other  hand, 
it  seems  probable  that  a  portion  of  it  may  be  actually  formed  in  the 
system,  by  the  union  of  a  portion  of  the  oxygen  absorbed  in  the  lungs, 
with  the  hydrogen  of  the  combustible  matters  of  the  blood.  In  the 
various  forms  of  saccharine  and  farinaceous  aliments,  the  proportions 
of  hydrogen  and  oxygen  are  such  as  would  of  themselves  form  water, 
when  the  carbon  is  withdrawn ;  but  in  oily  and  fatty  matters,  the 
proportion  of  oxygen  is  far  too  small  thus  to  neutralize  the  hydrogen  ; 
and  it  seems  likely  that,  by  their  oxidation  in  the  blood,  as  by  their 
combustion  elsewhere,  water  is  actually  generated  by  the  union  of 
atmospheric  oxygen  with  their  hydrogen,  whilst  carbonic  acid  is  pro- 
duced by  its  union  with  their  carbon. 

702.  Along  with  the  water  thus  extricated  from  the  lungs,  a  certain 
amount  of  organic  matter  is  set  free.  If  the  fluid  be  collected  in  a 
closed  vessel,  and  be  exposed  to  warmth,  a  very  evident  putrid  odour 
is  exhaled  from  it ;  and  if  the  expired  air  be  made  to  pass  through 
sulphuric  acid,  that  liquid  is  coloured  red.  Every  one  knows  that  the 
breath  itself  possesses,  occasionally  in  some  persons,  and  constantly  in 
others,  a  fetid  taint ;  when  this  does  not  proceed  from  carious  teeth, 
ulcerations  in  the  air-passages  or  lungs,  or  other  similar  causes,  it  must 
result  from  the  excretion  of  the  odorous  matter,  in  combination  with 
watery  vapour,  from  the  pulmonary  surface.  That  this  is  the  true 
account  of  it  seems  evident,  from  the  analogous  phenomenon  of  the 
exhalation  of  turpentine,  camphor,  alcohol,  and  other  odorous  sub- 
stances, which  have  been  introduced  into  the  venous  system,  either 
by  natural  absorption,  or  by  direct  injection ;  and  also  from  the  sud- 
denness with  which  the  odour  manifests  itself,  when  the  digestive 
apparatus  is  slightly  disordered. 

5.  Effects  of  Insufficiency^  or  Suspension^  of  the  Aerating  Process, 

703.  The  change  which  the  Blood  undergoes,  by  being  brought 
into  relation  with  atmospheric  air  in  the  respiratory  organs,  is  so 
important  to  life,  that  the  entire  suspension  of  it  inevitably  produces 
a  fatal  termination,  at  no  remote  period ;  and  if  it  be  insufficiently 
performed,  various  disorders  in  the  system  are  nearly  sure  to  manifest 
themselves.  The  state  which  is  induced  by  the  entire  suspension  of 
the  aerating  process,  is  termed  Asphyxia  ;  a  word  which  literally 
means  the  absence  of  pulse,  and  would  be  applicable,  therefore,  to  the 
stoppage  of  the  circulation  from  any  cause  ;  though  it  is  usually  em- 
ployed to  designate  the  particular  condition,  resulting  from  suspended 
respiration.  Asphyxia  may  be  produced  in  aquatic  animals,  as  well 
as  in  those  which  breathe  air,  by  cutting  them  off  from  the  influence 
of  the  atmosphere  ;  for  if  a  Fish  be  placed  in  water  from  which  the 
air  has  been  expelled  by  boiling,  it  is  precisely  in  the  condition  of  an 
air-breathing  animal  placed  in  a  vacuum,  since  it  has  no  power  of 
obtaining  oxygen  by  decomposing  the  water  it  inhabits,  and  is  en- 
tirely dependent  for  the   aeration  of  its  blood,  upon  the  air  that  is 


400  ASPHYXIA  ;--ITS  PHENOMENA. 

absorbed  by  the  liquid.  Again,  if  a  fish  be  placed  in  water  impreg- 
nated with  carbonic  acid,  its  death  is  nearly  as  instantaneous  as  that 
of  an  air-breathing  animal  immersed  in  an  atmosphere  of  that  gas. 

704.  Asphyxia  may  result  from  a  great  variety  of  causes.  Thus 
there  may  be  a  mechanical  obstruction  to  the  entrance  of  air  through 
the  trachea;  as  in  hanging,  strangulation,  or  drowning;  or  as  in 
occlusion  of  the  aperture  of  the  glottis,  by  cedema  of  its  lips,  or  by  the 
presence  of  a  foreign  body  in  the  larynx.  Or,  again,  the  passage  may 
be  perfectly  free,  and  yet  no  air  may  enter,  in  consequence  of  some 
obstacle  to  the  performance  of  the  respiratory  movements.  This 
obstacle  may  be  mechanical ;  as  when  a  quantity  of  earth  has  fallen 
round  the  body,  in  such  a  manner  as  completely  to  prevent  the  disten- 
sion of  the  chest  and  abdomen.  Or  it  may  result  (and  this  is  a  most 
frequent  occurrence)  from  torpidity  or  complete  inactivity  of  the  gan- 
glionic centre,  which  is  concerned  in  the  respiratory  actions ;  or  from 
interruption  to  the  transmission  of  its  influence  along  the  nervous 
trunks.  Further,  when  there  is  no  obstacle  to  the  free  ingress  or 
egress  of  air.  Asphyxia  may  be  produced  by  the  want  of  oxygen  in 
the  atmosphere  that  is  respired,  or  by  the  presence  of  carbonic  acid 
in  too  large  an  amount.  And  the  presence  of  other  gases,  which  exert 
a  directly  poisonous  influence  on  the  blood, — such  as  sulphuretted 
hydrogen, — produces  a  state,  which  may  be  included  under  the  same 
general  description. 

705.  Now  when,  from  any  of  these  causes,  the  free  exchange  of 
carbonic  acid  for  oxygen  in  the  pulmonary  capillaries  is  checked,  the 
first  effect  of  the  interruption  appears  to  be,  the  stagnation  of  the 
blood  in  the  pulmonary  capillaries.  This  stagnation  is  evidently  due, 
not  to  any  deficiency  of  power  in  the  heart ;  for  that  organ  is  not  yet 
affected ;  but  to  the  insufficiency  of  the  heart's  power,  acting  alone, 
to  drive  the  blood  through  the  pulmonary  capillaries;  the  force  which 
should  be  generated  by  chemical  changes  in  them  (§  598),  being 
deficient.  The  stagnation  is  not,  however,  complete  at  first ;  since 
the  quantity  of  oxygen  contained  in  the  lungs  is  sufficient  to  produce 
an  imperfect  arterialization  of  the  blood ;  and  the  blood  thus  partially 
changed  is  transmitted  to  the  left  side  of  the  heart,  and  is  thence  pro- 
pelled to  the  system.  Owing  to  its  half-venous  condition,  it  cannot 
exert  its  usual  stimulating  influence  on  the  tissues,  especially  the 
muscular  and  nervous ;  and  their  powers  are  consequently  weakened. 
For  the  same  reason,  it  does  not  receive  its  usual  auxiliary  force  in 
the  systemic  capillaries  (§  599);  since  the  changes,  which  it  ought  to 
undergo  in  them,  can  only  be  partially  performed. 

706.  As  the  air  included  in  the  lungs  loses  more  and  more  of  its 
oxygen,  and  is  more  and  more  charged  with  carbonic  acid,  the  aera- 
tion of  the  blood  in  the  pulmonary  capillaries  becomes  more  and  more 
imperfect ;  the  quantity  of  blood  which  is  allowed  to  return  to  the 
heart  is  gradually  diminished,  and  its  condition  becomes  more  and 
more  venous;  and  at  last,  the  pulmonary  circulation  is  altogether  sus- 
pended.   From  the  relation  which  the  respiratory  circulation  bears  to 


ASPHYXIA  ;— ITS  PHENOMENA  AND  TREATMENT.  401 

the  systemic,  in  all  the  higher  classes  of  animals,  save  Reptiles,  it 
follows  that  the  systemic  circulation  must  in  like  manner  be  brought 
to  a  stand.  The  venous  blood  accumulates  in  the  pulmonary  artery, 
in  consequence  of  the  obstruction  of  its  capillaries ;  it  distends  the 
right  cavities  of  the  heart ;  and  the  accumulation  extends  to  the 
venous  system  of  the  body  in  general,  especially  affecting  those  or- 
gans which  naturally  receive  a  large  quantity  of  venous  blood,  such 
as  the  liver  and  spleen.  The  arterial  system,  on  the  other  hand,  is 
emptied  in  a  corresponding  degree;  nearly  all  its  blood  having  passed 
through  the  systemic  capillaries;  and  no  fresh  supplies  being  received 
from  the  heart.  From  this  deficiency,  and  from  the  venous  character 
of  the  blood  which  the  systemic  arteries  do  contain,  it  results  that  the 
nervous  and  muscular  systems  lose  their  power;  insensibility  comes 
on,  at  first  accompanied  with  irregular  convulsive  movements ;  but 
in  a  short  time  there  is  a  total  cessation  of  all  movement  except  that 
of  the  heart ;  and  the  pulsations  of  that  organ  become  feebler  and 
feebler,  until  they  cease  altogether.  The  immediate  cause  of  the 
cessation  of  the  heart's  action  appears  to  be  different  on  the  two 
sides.  Both  are  equally  affected  by  the  want  of  arterial  blood  in  the 
capillaries  of  their  own  substance;  but  the  right  side  suffers  from 
over-distension,  which  produces  a  sort  of  paralysis  of  its  muscular- 
tissue  ;  whilst  the  left  side  retains  its  contractility,  but  is  not  excited 
to  contraction,  for  want  of  the  stimulus  of  arterial  blood  in  its  cavi- 
ties. 

707.  In  those  warm-blooded  animals,  which  are  not  endowed  with 
any  special  provision  for  enabling  them  to  sustain  life  during  the  pro- 
longed suspension  of  the  respiratory  process,  insensibility  and  loss  of 
voluntary  power  almost  invariably  supervene  within  a  minute  and  a 
half,  after  the  admission  of  air  to  the  lungs  has  been  entirely  prevent- 
ed ;  though  the  respiratory  efforts  and  convulsive  actions,  which  are 
dependent  upon  the  medulla  oblongata  and  spinal  cord,  may  continue 
for  a  minute  or  tw^o  longer.  The  circulation  generally  comes  to  a 
complete  stand  within  ten  minutes  at  farthest. — The  chief  exceptions 
are  in  the  case  of  diving  animals,  which  are  provided  with  large 
arterial  and  venous  reservoirs,  that  serve  to  maintain  the  circulatioa 
during  a  prolonged  suspension  of  the  respiratory  process  ;  for  the  arte- 
rial plexuses  being  ordinarily  filled,  they  afford  a  supply  of  aerated 
blood  to  the  systemic  capillaries,  when  other  blood  is  wanting ;  and 
the  reservoirs  connected  with  the  venous  system,  which  were  pre- 
viously empty,  receive  this  blood,  and  prevent  it  from  exercising; 
■undue  pressure  on  the  heart.  To  such  an  extent  is  this  provision, 
carried  in  some  animals,  that  the  Whale  has  been  known  to  remain 
under  water  for  an  hour.  Another  exception  exists  in  the  case  of 
hybernating  Mammals,  which  are  reduced  for  a  time  to  the  condition 
of  cold-blooded  animals;  and  which  can,  like  the  latter,  sustain  a 
prolonged  suspension  of  the  aerating  procees.  And  there  is  reason 
to  believe  that,  in  the  state  of  Syncope  or  fainting, — in  which  the 
circulation  is  already  reduced  to  a  very  low  amount,  in  consequence 
26 


402      ASPHYXIA  ;— ITS  PHENOMENA  AND  TREATMENT. 

of  a  partial  failure  in  the  heart's  power,  all  the  functions  of  the  body 
being  nearly  suspended,  and  the  demand  for  aeration  being  conse- 
quently very  small, — the  respiration  may  be  suspended  for  a  long 
period,  even  in  the  JHuman  subject,  without  fatal  results.  Thus  more 
than  one  case  has  been  credibly  recorded,  in  which  recovery  has  taken 
place  after  complete  submersion  for  more  than  three-quarters  of  an 
hour ;  and  it  is  probable  that,  in  these  instances,  a  state  of  Syncope 
came  on  at  the  moment  of  immersion,  through  the  influence  of  mental 
emotion,  or  of  concussion  of  the  brain. 

708.  In  the  restoration  of  an  animal  from  the  state  of  Asphyxia,  it 
is  above  all  things  of  importance  to  renew  the  air  in  the  lungs ;  for  in 
this  way  the  blood  in  the  pulmonary  capillaries  will  be  aerated  ;  the 
capillary  circulation  will  be  re-established  ;  the  right  side  of  the  heart 
will  be  relieved  of  its  excessive  load  of  venous  blood  ;  and  the  left 
side  will  receive  the  stimulus  of  a  fresh  supply  of  arterial  blood  ;  so 
that,  if  its  movements  have  not  ceased  altogether,  it  may  be  speedily 
restored  to  due  activity.  At  the  same  time,  the  temperature  of  the 
body  should  be  kept  up  by  artificial  warmth ;  and  the  circulation  in 
the  skin  should  be  excited  by  friction.  Where  no  other  means  are 
at  hand  for  introducing  pure  air  into  the  lungs  (of  which  means  the 
application  of  galvanism  along  the  course  of  the  phrenic  nerve,  so 
as  to  produce  contraction  of  the  diaphragm,  will  probably  be  the 
most  effectual),  the  object  may  be  attained  by  forcibly  compressing 
the  trunk  on  all  sides,  so  as  to  empty  the  lungs  as  much  as  possi- 
ble, and  then  allowing  the  chest  to  dilate  again,  by  the  elasticity 
of  its  walls.  In  this  manner,  a  large  proportion  of  the  carbonic 
acid  may  be  expelled,  and  a  considerable  proportion  of  the  fresh  air 
introduced,  in  the  course  of  a  few,  minutes.  If  air  be  blown  into 
the  lungs  by  the  bellows,  great  care  must  be  taken  to  prevent  the 
employment  of  too  much  force,  which  is  likely  to  produce  rupture  of 
the  air-cells. 

709.  Now^  when,  from  the  more  prolonged  action  of  various  causes, 
that  impede  the  due  performance  of  the  respiratory  function,  the 
aeration  of  the  blood  in  the  lungs  is  insufficient  for  health,  though  not 
such  as  to  produce  a  complete  stagnation  of  the  movement,  a  variety 
of  results  may  follow ;  of  which  some,  or  others,  will  manifest  them- 
selves according  to  the  condition  of  the  general  system,  and  the  pecu- 
liarities of  the  individual.  Thus  deficient  respiration  has  an  undoubted 
tendency  to  produce,  in  some  persons,  what  is  termed  "  fatty  degene- 
ration" of  the  liver;  the  fatty  matter,  which  ought  to  be  eliminated 
by  the  respiratory  process,  being  thrown  upon  the  liver  to  be  sepa- 
rated by  it,  and  distending  its  cells  (§  723).  And  there  is  reason  to 
believe,  that  a  similar  cause  may  produce  fatty  degeneration  of  the 
kidney,  in  cases  where  there  is  a  peculiar  determination  of  blood  to 
that  organ.  Again,  the  due  elaboration  of  the  fibrin  of  the  blood  is 
undoubtedly  prevented  by  an  habitually  deficient  respiration  ;  and 
various  diseases,  which  result  from  the  imperfect  performance  of  this 
elaboration,  consequently  manifest  themselves.     The  Scrofulous  dia- 


1 


OF  THE  SECRETING  PROCESS  IN  GENERAL.  403 

thesis  is  thus  frequently  connected  with  an  unusually  small  capacity 
of  the  chest. — Further,  an  habitual  deficiency  of  respiration  may  im- 
pede, though  it  does  not  check,  the  circulation  in  the  lungs  ;  and  thus 
a  tendency  arises,  in  various  pulmonary  diseases,  to  an  overloading  of 
the  pulmonary  arteries,  to  a  dilatation  of  the  right  cavities  of  the 
heart,  and  to  a  congestion  of  the  venous  system  in  general,  as  marked 
by  lividity  of  the  surface,  by  venous  pulsation,  &c.  This  state  may 
result,  not  merely  from  obstruction  in  the  lungs  themselves,  but  from 
deficiency  of  the  respiratory  movements,  consequent  upon  torpidity  of 
the  medulla  oblongata  (as  in  apoplexy  and  narcotic  poisoning),  or 
upon  partial  interruption  of  the  nervous  circle  requisite  for  all  reflex 
movements.  Thus  when  the  par  vagum  is  divided,  the  number  of 
respiratory  movements  is  greatly  diminished,  and  a  partial  stagnation 
of  the  blood  in  the  lungs  is  the  result.  The  same  happens  in  certain 
forms  of  typhoid  fever,  in  which  the  respiratory  movements  are  pre- 
ternaturally  slow,  in  consequence  of  torpidity  of  the  medulla  oblon- 
gata. Now  in  this  state,  an  effusion  of  the  watery  part  of  the  blood 
into  the  air-cells  of  the  lungs  (as  in  other  cases  of  obstructed  circula- 
tion) is  very  liable  to  occur ;  and  w^hen  the  lungs  are  thus  loaded 
with  fluid,  the  respiratory  process  is  still  more  impeded,  and  the  dis- 
order has  thus  a  tendency  to  increase  itself. 


CHAPTER  IX. 


OF  SECRETION. 


1.   Of  the  Secreting  process  in  general;  and  of  the  Instruments  by 
which  it  is  effected, 

710.  We  have  seen  that,  in  the  process  of  Nutrition,  the  circulat- 
ing current  not  only  deposits  the  materials,  which  are  required  for  the 
renovation  of  the  solid  tissues ;  but  also  takes  back  the  substances, 
which  are  produced  by  the  decay  of  these,  and  which  are  destined  to 
be  thrown  off  from  the  body.  We  have  also  seen  that  it  supplies  the 
materials  of  certain  fluids,  which  are  separated  from  it  to  effect  various 
purposes  in  the  economy ; — such  as  the  Salivary  and  Gastric  fluids, 
which  have  for  their  office  to  assist  in  the  reduction  of  the  food.  Now 
the  process,  by  which  the  fluids  of  the  latter  kind  are  separated  from 
the  Blood,  is  precisely  the  same  in  character  as  that,  by  which  the 
products  of  decay  are  eliminated  from  it ;  and  the  structure  of  the  or- 
gans concerned  in  the  two  is  essentially  the  same.  Hence  both  pro- 
cesses are  commonly  included  under  the  general  term  Secretion,  which 
simply  denotes  separation.  Considered  in  its  most  general  point  of 
view,  this  designation  may  be  applied  to  every  act,  by  which  sub- 


404  NATURE  OF  THE  SECRETING  PROCESS. 

stances  of  any  kind  are  separated  from  the  blood.  Thus  the  function 
of  the  floating  cells,  which  are  concerned  in  the  production  of  Fibrin 
(§  213),  may  be  termed  one  of  secretion;  because  they  draw  from 
the  blood  a  supply  of  Albumen,  upon  which  their  converting  action 
is  exercised ;  but  as  the  product  of  their  operation  is  returned  to  the 
blood  again,  and  is  employed  for  higher  purposes  in  the  economy, 
the  process  is  usually  termed  Assimilation.  In  the  same  manner,  the 
elaborating  action  of  the  Lymphatic  Glands,  with  the  Spleen,  Thy- 
mus Gland,  &c.,  is  not  usually  termed  Secretion;  since,  although  it 
is  exercised  upon  matter  drawn  from  the  blood,  the  product  appears 
to  be  delivered  back  into  the  circulating  current,  through  the  medium 
of  the  Lymphatic  System  (Chap.  V).  With  much  more  justice,  how- 
ever, the  process  of  Respiration  may  be  regarded  as  one  of  Secretion ; 
for  it  consists,  as  we  have  seen,  in  the  constant  elimination  of  a  sub- 
stance from  the  blood,  which  cannot  be  retained  in  it  without  the 
most  injurious  consequences. 

711.  There  is  an  important  difference  in  the  characters  of  the  prin- 
cipal products  of  the  Secreting  process ;  which  is  connected  with  the 
purposes  that  are  to  be  answered  by  their  separation.  Some  of  these 
products  are  altogether  different  from  the  ordinary  constituents  of  the 
animal  fabric,  and  from  the  materials  which  the  blood  supplies  for  the 
nutrition  of  these.  So  different  are  they,  that  their  presence  in  the 
circulating  current  has  an  injurious  effect;  and  the  great  object  of 
their  separation  is  the  maintenance  of  the  purity  of  the  blood.  These 
poisons,  for  such  they  may  be  considered,  are  generated  in  the  system 
by  the  decay  and  decomposition  to  which  its  several  parts  are  liable ; 
and  they  are  just  as  noxious  to  it,  as  if  they  were  absorbed  from  without. 
We  have  seen  that  the  retention  of  Carbonic  acid  in  the  blood  for 
even  a  few  minutes  is  fatal ;  both  by  putting  a  stop  to  the  circulation, 
and  by  acting  unfavourably  upon  the  substance  of  some  of  the  most 
important  organs  in  the  body.  The  same  fatal  result  attends  the 
retention  of  Urea  and  of  Biliary  matter,  which  are  among  the  other 
products  of  the  decomposition  of  the  tissues  ;  but,  although  as  certain, 
it  is  not  so  speedy,  because  the  general  circulation  is  not  affected  by 
the  loss  of  secreting  power  on  the  part  of  the  Kidneys  and  the  Liver, 
and  because  the  accumulation  of  the  noxious  matter  is  slower. — On 
the  other  hand,  the  ingredients  that  are  met  with  in  those  secreted 
fluids,  which  are  destined  to  answer  some  purpose  in  the  economy, 
almost  invariably  bear  a  close  correspondence  with  the  ordinary  ma- 
terials of  the  blood.  Thus  in  the  Salivary,  Gastric,  Pancreatic,  and 
Lachrymal  fluids,  the  principal  part  of  the  solid  matter  consists  of  the 
saline  and  of  the  albuminous  constituents  of  the  blood, — the  latter  in 
a  more  or  less  altered  condition.  In  Milk,  again,  we  trace  the  ordi- 
nary constituents  of  the  blood,  with  very  little  change.  Thus  it 
appears,  that  the  separation  of  these  fluids  is  not  required  so  much  to 
maintain  the  Blood  in  a  state  of  purity,  as  to  supply  what  is  needed 
for  some  subsequent  operation  in  the  economy ;  and  hence,  if  the 
secreting  process  be  interrupted,  in  the  case  of  any  one  of  them,  the 


NATURE  OF  THE  SECRETING  PROCESS.  405 

suspension  has  usually  no  further  effect,  than  that  of  disturbing  the 
process  to  which  the  fluid  is  usually  subservient.  If  the  secretion  of 
Gastric  fluid  be  checked,  for  example,  under  the  influence  of  strong 
mental  emotion,  the  Digestive  operation  is  prevented  from  taking 
place. 

712.  The  essential  character  of  the  true  Secreting  operation  seems 
to  consist, — not  in  the  nature  of  the  action  itself,  for  this  is  identical 
with  those  of  Assimilation  and  Nutrition,  being  (as  we  have  seen, 
§  239),  a  process  of  cell-growth, — but  in  the  position  in  which  the 
cells  are  developed,  and  the  mode  in  which  the  products  of  their 
action  are  afterwards  disposed  of.  Thus  the  cells  at  the  extremities 
of  the  intestinal  Villi  (§  241),  the  cells  of  which  the  Adipose  tissue 
is  made  up  (§  259),  and  the  cells  of  which  the  greater  part  of  the 
substance  of  the  Liver  is  formed  (§  239),  all  have  an  attraction  for 
fatty  matter  ;  and  draw  it  from  the  neighbouring  fluids,  at  the  expense 
of  which  they  are  developed,  to  store  it  up  in  their  own  cavities. 
But  the  cells  of  the  first  kind,  when  they  have  come  to  maturity,  set 
free  their  contents,  which  are  delivered  to  the  absorbent  vessels,  to 
be  introduced  into  the  circulating  current : — those  of  the  second  kind 
seem  more  permanent  in  their  character,  and  retain  their  contents,  so 
as  to  form  part  of  the  ordinary  tissues  of  the  body,  until  they  are  re- 
quired to  give  them  up  for  other  purposes,  when  the  matters,  which 
they  have  temporarily  separated  from  the  circulating  current,  are 
restored  to  it  again  without  change  ; — and  the  cells  of  the  third  class, 
when  they  liberate  their  contents  (which  they  are  continually  doing), 
cast  them  forth  into  the  hepatic  ducts,  by  which  they  are  carried  into 
the  intestinal  canal,  whence  a  portion  of  them  at  least  is  directly  con- 
veyed out  of  the  body. 

713.  It  is,  then,  in  the  position  of  the  Secreting  cells, — which  causes 
the  product  of  their  action  to  be  delivered  upon  a  Jree  surface,  com 
municating,  more  or  less  directly,  with  an  external  outlet, — that  their 
distinctive  character  depends.  All  the  proper  Secretions '  zve  thus 
either  poured  out  upon  the  exterior  of  the  body,  or  into  cavities  pro- 
vided with  orifices  that  lead  to  it.  Thus  we  shall  see  that  a  con- 
siderable quantity  of  solid  matter,  and  a  very  large  quantity  of  fluid, 
of  which  it  is  desirable  that  the  system  should  be  freed,  are  carried 
off  from  the  Cutaneous  surface.  Another  most  important  secretion, 
containing  a  large  quantity  of  solid  matter,  and  serving  also  to  regu- 
late the  quantity  of  fluid  in  the  body, — namely,  the  Urinary, — is  set 
free  by  a  channel  expressly  adapted  to  convey  it  directly  out  of  the 
body.  The  same  may  be  said  of  the  Mammary  secretion  ;  which  is 
separated  from  the  blood,  not  to  preserve  its  purity,  nor  to  answer 
any  purpose  in  the  economy  of  the  individual,  but  to  afford  nutriment 
to  another  being.  And  of  the  matters  secreted  by  the  very  numerous 
glandulse  situated  in  the  walls  of  the  intestinal  canal,  a  great  part  are 
obviously  poured  into  it  for  no  other  purpose,  than  that  they  may  be 
carried  out  of  the  body  by  the  readiest  channel. 

714.  The  cells  covering  the  simple  membranes  that  form  the  free 
surfaces  of  the  body,  whether  external  or  internal,  are  all  entitled  to 


406         CHARACTER  OF  GLANDULAR  STRUCTURE. 

be  regarded  as  secreting  cells ;  since  they  separate  from  the  blood 
various  products  which  are  not  again  to  be  returned  to  it.  But  the 
secreting  action  of  some  of  these  seems  to  have  for  its  object  the 
protection  of  the  surface  ;  thus  the  epidermic  cells  secrete  a  horny 
matter,  by  which  density  and  firmness  are  imparted  to  the  cuticle ; 
whilst  by  the  epithelial  cells  of  the  Mucous  Membrane  of  the  alimen- 
tary canal,  and  of  other  parts,  their  protective  Mucus  seems  to  be 
elaborated.  But  in  general  we  find  that  special  organs,  termed  Glands, 
are  set  apart  for  the  production  of  the  chief  secretions ;  and  we  have 
now  to  consider  the  essential  structure  of  these  organs,  and  the  mode 
of  their  operation. — A  true  Gland  may  be  said  to  consist  of  a  closely 
packed  collection  of  follicles,  all  of  which  open  into  a  common  chan- 
nel, by  which  the  product  of  the  glandular  action  is  collected  and 
delivered.  The  follicles  contain  the  secreting  cells  in  their  cavities  ; 
whilst  their  exterior  is  in  contact  with  a  network  of  blood-vessels, 
from  which  the  cells  draw  the  materials  of  their  growth  and  deve- 
lopment (Fig.  90).  In  any  one  of  the  higher  animals,  we  may  trace 
out  a  series  of  progressive  stages  of  complexity,  in  the  various  glands 
included  within  their  fabric  ;  and  in  following  any  one  of  the  glands, 
that  attain  the  highest  degree  of  development  (such  as  the  Liver  or 
Kidney),  through  the  ascending  scale  of  the  Animal  series,  we  should 
trace  a  very  similar  gradation  from  the  simplest  to  the  most  complex 
form. 

715.  That  there  is  nothing  in  the  form  or  disposition  of  the  com- 
ponents of  the  glandular  structure,  which  can  have  any  influence 
upon  the  character  of  the  secretion  it  elaborates,  is  evident  from  the 
fact,  that  the  very  same  product, — e.  g.,  the  Bile,  or  the  Urine, — is 
found  to  issue  from  nearly  every  variety  of  secreting  structure,  as  we 
trace  it  through  the  different  groups  of  the  Animal  kingdom.  The 
peculiar  power,  by  which  one  organ  separates  from  the  blood  the 
elements  of  the  Bile,  and  another  the  elements  of  the  Urine,  whilst  a 
third  merely  seems  to  draw  off  a  certain  amount  of  its  albuminous 
and  saline  constituents,  is  obviously  the  attribute  of  the  ultimate 
secreting  cells,  which  are  the  real  agents  in  the  secreting  process 
(§  239).  Why  one  set  of  cells  should  secrete  bile,  another  urea, 
and  so  on,  we  do  not  know ;  but  we  are  equally  ignorant  of  the 
reason  for  which  one  set  of  cells  converts  itself  into  Bone,  another 
into  Muscle,  and  so  on.  This  variety  in  the  endowments  of  the  cells, 
by  whose  aggregation  and  conversion  the  fabric  of  the  higher  Ani- 
mals is  made  up,  is  a  fact  which  we  cannot  explain,  and  which  must 
be  regarded  (for  the  present,  at  least),  as  one  of  the  "  ultimate  facts" 
of  Physiological  Science. 

716.  Passing  by  the  extended  membranous  surfaces,  and  the  pro- 
tective cells  with  which  they  are  covered,  we  find  that  the  simplest 
form  of  a  secreting  organ  is  composed  of  an  inversion  of  that  suriface, 
into  a  series  of  follicles,  which  discharge  their  contents  upon  it  by 
separate  orifices.  Of  this  we  have  an  example  in  the  ^a^/ric  follicles, 
even  in  the  higher  animals ;  the  apparatus  for  the  secretion  of  the 
Gastric  fluid  never  attaining  any  higher  condition  than  that  of  a 


SIMPLEST  FORMS  OF  GLANDULAR  STRUCTURE. 


407 


series  of  distinct  follicles,  lodged  in  the  walls  of  the  stomach,  and 
pouring  their  products  into  its  cavity  by  separate  apertures.     In  Fig. 


Fig.  103. 


Fig.  104. 


Glandular  follicles  in  ventriculus 
succenturiatus  of  Falcon. 


Origin  of  the  Liver  from  the  intestinal  wall,  in  the 
embryo  of  the  Fowl,  on  the  fourth  day  of  incubation  : 
— a,  heart ;  b,  intestine ;  c,  everted  portion  giving  ori- 
gin to  liver ;  d,  liver ;  e,  portion  of  yolk-bag. 


Fig.  105. 


103  is  represented  a  portion  of  the  Ventriculus  succenturiatus  of  a 
Falcon  ;  in  which  the  simplest  form  of  such  follicles  is  seen.  A  some- 
what more  complex  condition  is  seen  in  some  of  the  Gastric  follicles 
of  the  Human  stomach  (Fig.  75) ;  the 
surface  of  each  follicle  being  further 
extended  by  a  sort  of  doubling  upon 
itself,  so  as  to  form  the  commencement 
of  secondary  follicles,  which  open  out 
of  the  cavity  of  the  primary  one. — 
Now  a  condition  of  this  kind  is  common 
to  all  glands,  in  the  first  stage  of  their 
evolution  ;  and  in  this  stage  we  meet 
with  them,  either  by  examining  them 
in  the  lowest  animals  in  which  they 
present  themselves,  or  by  looking  to  an 
early  period  of  their  embryonic  deve- 
lopment in  the  highest.  Thus,  for  ex- 
ample, the  Liver  consists,  in  certain 
Polypes  and  in  the  lowest  MoUusca,  of 
a  series  of  isolated  follicles,  lodged  in 
the  walls  of  the  stomach,  and  pouring 
their  product  into  its  cavity  by  separate  orifices  ;  these  follicles  being 
recognized  as  constituting  a  biliary  apparatus,  by  the  colour  of  their 
secretion.     And  in  the  Chick,  at 

an  early  period  of  incubation,  the  ^ig.  loe. 

condition  of  the  Liver  is  essen- 
tially the  same  with  the  preced- 
ing ;  for  it  consists  of  a  cluster 
of  isolated  follicles,  not  lodged 
in  the  walls  of  the  intestine,  but 
clustered  round  a  sort  of  bud  or 
diverticulum  ofthe  intestinal  tube, 
which  is  the  first  condition  of  the 


Rudimentary  Pancreas  from  Cod ;— a, 
pyloric  extremity  of  stomach ;  b,  intes- 
tine. 


Mammary  Gland  of  Ornithorhyucus. 


408  DIFFERENT  FORMS  OF  GLANDULAR  STRUCTURE. 

hepatic  duct,  and  into  which  they  discharge  themselves  (Fig.  104). 
So,  again,  the  Pancreas  first  presents  itself  in  the  condition  of  a  group 
of  prolonged  follicles,  or  cceca,  clustered  round  the  commencement  of 
the  intestinal  tube  (Fig.  105);  which  is  its  permanent  condition  in 
many  Fishes.  And  the  Mammary  Gland  possesses  an  equally  simple 
structure  in  the  lowest  of  all  the  Mammalia  (to  which  group  it  is  re- 
stricted ; — namely,  in  the  Ornithorhyncus  (Fig.  106). 

717.  The  next  grade  of  complexity  is  seen,  where  a  cluster  of  the 
ultimate  follicles  open  into  one  common  duct,  which  discharges  their 
product  by  a  single  outlet ;  a  single  gland  often  containing  a  number 
of  such  clusters,  and  having,  therefore,  several  excretory  ducts.  A 
good  example  of  such  a  condition,  in  which  the  clusters  remains  iso- 
lated from  one  another,  is  seen  in  the  Meibomian  glands  of  the  eye- 
lid (Fig.  107);  each  of  which  consists  of  a  double  row  of  follicles,  set 
upon  a  long  straight  duct,  that  receives  the  products  of  their  secreting 
action,  and  pours  them  out  upon  the  edge  of  the  eyelid.  And  of  the 
more  complex  form,  in  which  a  number  of  such  clusters  are  bound 
together  in  one  glandular  mass,  we  have  an  illustration  in  the  acces- 
sory glands  of  the  genital  apparatus,  in  several  animals,  which  dis- 
charge their  secretion  into  the  urethra  by  numerous  outlets  (Fig. 
108);  or  in  the  Mammary  glands  of  Mammalia  in  general,  the  ulti- 
mate follicles  of  which  are  clustered  upon  ducts  that  coalesce  to  a 

Fig.  107.  Fig.  108.  Fig.  109. 


Meibomian  glands  of  upper  Portion  of  Cowper's  gland,  Lobule  of  Lachrymal  Gland ; 

lid  of  new-born  infant.  from  Hedgehog;  the  follicles  from  foetal  sheep, 

distended  with  air. 

considerable  extent,  though  continuing  to  form  several  distinct  trunks 
even  to  their  termination.  Such  glands  may  be  subdivided,  there- 
fore, into  glanduU  or  lobules,  that  remain  entirely  distinct  from  each 
other  (Fig.  109).— In  the  highest  form  of  Gland,  however,  all  the 
ducts  unite;  so  as  to  form  a  single  canal,  which  conveys  away  the 
products  of  the  secreting  action  of  the  entire  mass.  This  is  the  con- 
dition in  which  we  find  the  Liver  to  exist,  in  most  of  the  higher  ani- 
mals;  also  the  Pancreas,  the  Parotid  Gland,  and  many  others.  In 
•some  of  these  cases,  we  may  still  separate  the  gland  into  numerous 
distinct  lobules,  which  are  clustered  upon  the  excretory  duct  and  its 
branches,  like  grapes  upon  a  stalk ;  in  others,  however,  the  branches 


DEVELOPMENT  OF  GLANDS.  409 

of  the  excretory  duct  do  not  confine  themselves  to  ramifying,  but 
inosculate  so  as  to  form  a  network,  which  passes  through  the  whole 
substance  of  the  gland,  and  which  connects  together  its  different 
parts,  so  as  to  render  the  division  into  lobules  less  distinct.  This 
seems  to  be  the  case  in  regard  to  the  Liver  of  the  higher  Vertebrata. 
718.  Whatever  degree  of  complexity,  however,  prevails  in  the 
general  arrangement  of  the  elements  of  the  Glands  in  higher  animals, 
these  elements  are  themselves  everywhere  the  same,  consisting  of 
follicles  that  enclose  the  real  secreting  cells  (Figs.  110  and  111). 
Now  from  the  history  of  the  development  of  Glands  in  general,  it  ap- 
pears that  the  follicles  may  be  considered  dis  parent  cells;  and  that  the 

Fig.  110.  Fig.  111. 


Two  follicles  from  the  liver  of  Careinus  Ultimate   follicles  of  Mammary  gland, 

nuEnos  (Common  Crab), "with  their  contain-  with  their  secreting  cells,  a,  a; — b,  b,  the 

ed  secreting  cells.  nuclei. 

secreting  cells  in  their  interior  constitute  a  second  generation,  developed 
from  the  nuclei  or  germinal  spots  on  the  walls  of  the  first.  It  has  been 
pointed  out  by  Mr.  Goodsir,  that  the  continued  development  and  de- 
cay of  the  glandular  structure, — in  other  words,  the  elaboration  of  its 
secretion,  may  take  place  in  tw^o  different  modes.  In  one  class  of 
Glands,  the  parent-cell,  having  begun  to  develop  new  cells  in  its  in- 
terior, gives  way  at  one  point,  and  bursts  into  the  excretory  duct,  so 
as  to  become  an  open  follicle,  instead  of  a  closed  cell :  its  contained 
or  secondary  cells,  in  the  progress  of  their  own  growth,  draw  into 
themselves  the  matter  to  be  eliminated  from  the  blood,  and,  having 
attained  their  full  term  of  life,  burst  or  liquefy,  so  as  to  discharge 
their  contents  into  the  cavity  of  the  follicle,  whence  they  pass  by  its 
open  orifice  into  the  excretory  duct:  and  a  continual  new  production 
of  secondary  cells  takes  place  from  the  germinal  spot  or  nucleus,  at 
the  extremity  of  the  follicle,  which  is  here  a  permanent  structure.  In 
this  form  of  gland,  we  may  frequently  observe  the  secreting  cells  ex- 
isting in  various  stages  of  development  within  a  single  follicle  ;  their 
size  increasing,  and  the  character  of  their  contents  becoming  more 
distinct,  in  proportion  to  their  distance  from  the  germinal  spot  (which 
is  at  the  blind  termination  of  the  follicle),  and  their  consequent  proxi- 
mity to  the  outlet  (Fig.  110).  In  some  varieties  of  such  glands,  how- 
ever,— as  in  the  greatly  prolonged  follicles,  or  tubuli  uriniferi,  of  the 
kidney, — the  production  of  new  cells  does  not  take  place  from  a  single 
germinal  spot  at  the  extremity  of  the  follicle,  but  from  a  number  of 
points  scattered  through  its  entire  length. 

719.  In  the  second  type  of  Glandular  structures,  the  parent-cell 


410 


COMPARATIVE  STRUCTURE  OF  THE  LIVER. 


does  not  remain  as  a  permanent  follicle ;  but,  having  come  to  maturity 
and  formed  a  connection  with  the  excretory  duct,  it  discharges  its 
entire  contents  into  the  latter,  it  then  shrivels  up  and  disappears,  to  be 
replaced  by  newly-developed  follicles.  In  each  parent-cell  of  a  gland 
formed  upon  this  type,  we  shall  find  all  its  secondary  or  secreting  cells 
at  nearly  the  same  grade  of  development ;  but  the  different  parent- 
cells,  of  which  the  parenchyma  of  the  gland  is  composed,  are  in  very 
diff*erent  stages  of  growth,  at  any  one  period, — some  having  discharged 
their  contents  and  being  in  progress  of  disappearance,  whilst  others 
are  just  arriving  at  maturity  and  connecting  themselves  with  the 
excretory  duct;  others  exhibiting 'an  earlier  degree  of  development  of 
the  secondary  cells;  others  presenting  the  latter  in  their  incipient  con- 
dition; whilst  others  are  themselves  just  starting  into  existence,  and 
as  yet  exhibit  no  traces  of  a  second  generation. — The  former  seems  to 
be  the  usual  type  of  the  ordinary  Glands ;  the  latter  is  chiefly,  if  not 
entirely,  to  be  met  with  in  the  Spermatic  glands. 

2.   Of  the  Liver, 

720.  The  Liver  is  more  rarely  absent  than  any  other  Gland ;  being 
discoverable,  under  some  form  or  other,  in  all  but  the  very  lowest 
members  of  the  Animal  kingdom.  Its  simple  condition  in  the  higher 
Polypes  has  been  already  noticed  (§  716) ;  and  it  is  met  with,  under 
an  almost  equally  simple  form,  in  the  Star-fish.  As  we  ascend  the 
scale,  however,  w^e  find  it  assuming  a  much  greater  importance,  and 
presenting  a  great  increase  in  size.  This  is  particularly  the  case  in 
the  Molluscous  classes  ;  and  also  in  the  Crustacea, — a  class  which,  in 
mode  of  respiration  and  in  general  habits,  bears  a  great  resemblance  to 
the  MoUusca.  In  nearly  all  such  animals,  the  Liver  makes  up  a  large 
proportion  of  the  mass  of  the  body.  It  usually  consists  of  a  series  of 
large  follicles,  which  branch  out  into  smaller  ones  (Figs.  112  and  113), 


Fig.  112. 


Fig.  113. 


Lobule  of  Liver  of  Squilla  Mantis;  exterior. 


Lobule  of  Liver  of  Squilla  Mantis  cut  open. 


and  of  which  several  open  into  one  excretory  duct;  but  these  ducts 
remain  separate,  and  discharge  their  contents  into  the  intestine  by 
several  distinct  orifices. — In  Insects  and  other  air-breathing  Articu- 


STRUCTURE  OF  THE  LIVER. 


411 


Fig.  114. 


lata,  however,  the  Liver  is  much  less  developed  ;  and  its  type  remains 
much  simpler.  We  usually  find  it  consisting  of  a  small  number  of 
csecal  tubuli,  which  open  separately  into  the  intestinal  canal,  just 
below  the  stomach.  These  tubuli  are  often  so  long,  as  to  pass  several 
times  from  one  extremity  of  the  visceral  cavity  to  the  other,  being 
doubled  upon  themselves ;  in  other  instances,  we  find  that  the  prin- 
cipal tube  or  canal  is  beset  with  rows  of  short  follicles,  somewhat  in 
the  manner  of  Fig.  107.  But  they  never  cluster  together,  so  as  to 
form  a  solid  glandular  mass.  The  low  development  of  the  liver,  in 
these  animals,  bears  an  evident  relation  with  the  high  development 
of  their  respiratory  apparatus ;  whilst,  the  respiration  being  compara- 
tively feeble  in  the  aquatic  Mollusca  and  Crustacea,  the  development 
of  the  liver  in  those  classes  is  enormous. 

721.  There  is  much  difficulty  in  ascertaining  the  mode  in  which 
the  elementary  constituents  of  the  Liver  are  arranged,  in  the  fully- 
developed  condition  of  that  organ  in  the  higher  Vertebrata.  At  an 
early  period  of  its  development, 
as  already  remarked,  it  may  be 
easily  shown  to  consist,  in  the 
Fowl,  of  a  series  of  distinct  caeca, 
clustered  round  a  projection  from 
the  intestinal  canal,  and  opening 
separately  into  it  (Fig.  104) ;  and 
it  is  a  peculiarly  interesting  fact, 
that  this  very  condition  should 
exist  as  the  permanent  form  of  the 
Liver,  in  that  curious  little  fish, 
the  Amphioxus  or  Lancelot,  which 
retains  the  embryonic  type  in  so 
many  parts  of  its  conformation. 
In  the  Tadpole,  again,  the  distinct 
cseca  are  very  evident  (Fig.  114); 
but  here  we  see  that  the  projection 
of  the  intestinal  canal,  instead  of 
being  a  simple  wide  csecum,  has 

become  extended  in  length  and  contracted  in  diameter,  at  the  same 
time  dividing  and  subdividing,  so  as  to  form  an  arborescent  excretory 
duct,  whose  ramifications  extend  through  the  entire  glandular  mass. 
In  this  manner,  then,  is  formed  the  complex  system  of  hepatic  ducts, 
which  we  find  in  the  liver  of  the  higher  Vertebrata,  branching  out 
from  the  main  trunk.  But  the  mode  in  which  the  ultimate  ramifica- 
tions of  these  are  arranged,  and  their  relations  with  the  secreting  cells, 
which  make  up  the  parenchyma  of  the  gland,  have  not  yet  been  fully 
elucidated.  The  following  are  the  principal  facts,  that  have  been 
ascertained  on  the  subject. 

722.  The  entire  Liver  is  made  up  of  a  vast  number  of  minute 
lobules,  of  irregular  form,  but  about  the  average  size  of  a  millet-seed. 
Each  of  these  lobules  contains  the  component  elements,  of  which  the 


Liver  of  Tadpole ;  showing  distinct  and  free 
caecal  terminations  of  the  biliary  ducts. 


412 


DISTRIBUTION  OF  BLOOD-VESSELS  OF  THE  LIVER. 


entire  organ  is  made  up ; — namely,  branches  of  the  hepatic  artery  and 
vein,  branches  of  the  portal  vein,  branches  of  the  hepatic  ducts,  and 
secreting  cells.  The  lobules  are  connected  together  in  part  by  areolar 
tissue,  but  in  great  part  by  the  anastomosis  of  the  blood-vessels  and 
hepatic  ducts,  which  supply  the  adjoining  lobules;  indeed  there  is 
frequently  no  definite  division  of  the  glandular  substance  into  lobules, 
other  than  that,  which  is  marked  out  by  the  arrangement  of  these 
canals  (Figs.  115  and  117).  The  branches  of  the  Hepatic  Artery  are 
principally  distributed  upon  the  walls  of  the  hepatic  ducts,  and  upon 
the  trunks  and  branches  of  the  portal  and  hepatic  veins,  supplying 
them  with  their  vasa  vasorum;  also  upon  Glisson's  capsule  and  its 
prolongations  into  the  substance  of  the  liver, — which  prolonga- 
tions form  the  greatest  part  of  the  connecting  structure,  that  holds 
together  the  several  elements.  There  is  strong  reason  to  believe, 
that  the  blood  which  the  liver  receives  from  the  hepatic  artery  is  not 
destined  to  supply  the  materials  for  the  biliary  secretion,  until  it  has 
become  venous  by  traveling  through  the  network,  in  which  it  is  sub- 
servient to  the  nutrition  of  the  tissues  it  permeates,  as  it  is  in  other 
parts  of  the  systemic  capillary  system. — The  supply  of  blood,  from 
which  the  materials  of  the  biliary  secretion  are  chiefly  drawn,  is 
afforded  by  the  Vena  PortcB,  which  collects  it  as  a  Vein  from  the  chy- 
lopoietic  viscera,  and  which  then  subdivides  as  an  Artery  to  distribute 
it  to  the  different  parts  of  the  Liver.  Its  branches  proceed  to  the  cap- 
sules of  the  lobules,  covering  the  whole  external  surface  of  the  latter 
with  their  ramifications,  and  sending  capillary  twigs  inwards,  which 
converge  towards  the  centre  of  each  lobule  (Fig.  115).     As  the  prin- 

Fig.  116. 


Horizontal  section  of  three  superficial  lobules, 
showing  the  two  principal  systems  of  blood-ves- 
sels ;  1, 1,  mtra-lobular  veins,  proceeding  from  the 
Hepatic  veins ;  2,  2,  inter-lobular  plexus,  formed 
by  branches  of  the  Portal  veins. 


Connection  of  the  lobules  of  the  Liver 
with  the  Hepatic  vein;  1,  trunk  of  the  vein; 
2,  2,  lobules  depending  from  its  branches, 
like  leaves  on  a  tree  ;  the  centre  of  each 
being  occupied  by  a  venous  twig— the  In- 
tralobular Vein. 


cipal  branches  of  these  veins  ramify  in  the  spaces  between  the  lobules, 
they  are  termed  in^er-lobular  veins.— On  the  other  hand,  the  branches 


HEPATIC  DUCTS,  AND  CELLS  OF  PARENCHYMA. 


413 


of  the  Hepatic  Vein  pass  from  the  trunks  to  the  centre  of  each  lobule, 
from  which  they  send  out  diverging  capillary  twigs  towards  the  cir- 
cumference ;  and  these  last,  coming  into  connection  with  the  converg- 
ing capillaries  of  the  portal  vein,  establish  a  free  capillary  communi- 
cation between  the  interior  and  exterior  of  each  lobule.  Thus  the 
portal  blood  is  first  distributed  to  its  exterior,  then  penetrates  its  sub- 
stance, and  then,  after  permeating  the  parenchymatous  substance  in 
numerous  minutely-divided  streams,  is  collected  and  carried  off  by  the 
hepatic  vein,  of  which  a  twig  originates  in  the  centre  of  each  lobule. 
Owing  to  the  peculiar  position  of  the  branches  of  the  hepatic  vein  in 
the  centre  of  each  lobule,  the  lobules  are  appended  to  its  mai^  trunks 
almost  in  the  manner  of  leaves  upon  a  stem  (Fig.  116). — Thje  precise 
relation  of  the  capillaries  of  the  hepatic  artery  with  those  of  the  por- 
tal and  venous  systems,  has  not  yet  been  well  ascertained ;  but  there 
seems  reason  to  believe,  with  Mr.  Kiernan,  that  the  arterial  capillaries 
discharge  themselves  into  the  ultimate  ramifications  of  the  portal  vein  ; 
and  that  thus  the  blood  of  the  former,  having  become  venous  by 
transmission  through  the  nutritive  capillaries  of  the  liver,  mingles 
with  the  other  venous  blood  collected  by  the  vense  portse,  to  supply 
the  materials  of  the  secretory  function,  which  are  eliminated  from  it 
during  its  passage  into  the  hepatic  vein. 

723.  The  Hepatic  Ducts  also  form  a  plexus,  which  surrounds  the 
lobules  ;  connecting  them  together,  and  sending  branches  towards  the 
interior  of  each.  The  mode  in  which  they  terminate,  however,  and 
the  precise  relation  in  which  they  stand  to  the  hepatic  cells,  which 
form  nearly  the  entire  parenchyma  of  the  Gland,  are  yet  unexplained. 


Fig.  118. 


Horizontal  section  of  two  superficial  lobules,  showing 
the  interlobular  plexus  of  biliary  ducts ;  1,  1,  intralobu- 
lar veins;  2,  2,  trunks  of  biliary  ducts,  proceeding  from 
the  plexus  which  traverses  the  lobules ;  3,  interlobular 
tissue ;  4,  parenchyma  of  the  lobules.    (After  Kiernan.) 


Glandular  cells  of  Liver:— a,  nucleus' 
,  nucleolus  ;  c,  adipose  particles. 


These  cells  are  of  a  flattened  spheroidal  form,  and  commonly  lie  in 
piles,  their  faces  adhering  to  one  another ;  and  these  piles  seem  to  be 
directed  especially  from  the  circumference  to  the  centre  of  each  lobule. 
Every  one  of  them  presents  a  distinct  nucleus;  and  the  cavity  of  the 
cell  is  filled  with  yellow  amorphous  biliary  matter,  having  one  or  two 
large  adipose  globules,  or  five  or  six  small  ones,  intermingled  with  it. 


414  CHEMICAL  COMPOSITION  OF  BILE. 

Their  diameter  is  usually  from  l-1500th  to  l-2000th  of  an  inch  ;  and 
they  are  easily  obtained  in  a  separate  condition,  by  scraping  a  piece 
of  fresh  Liver.  The  biliary  matter  which  they  contain,  marks  them 
out  as  the  real  agents  in  the  secreting  process  ;  this  process  consisting, 
it  is  evident,  in  the  growth  of  the  hepatic  cells,  w^hich,  in  the  course 
of  their  development,  eliminate  from  the  blood  the  biliary  matter,  for 
"which  they  have  a  special  affinity.  The  mode  in  which  the  particles 
thus  eliminated,  are  discharged  into  the  hepatic  ducts,  to  be  by  them 
conveyed  to  the  intestine,  cannot  be  understood,  until  the  relation 
between  the  secreting  cells  and  the  ultimate  ramifications  of  the  ducts 
shall  have  been  more  precisely  determined. 

724.  The  Bile  which  has  been  secreted  by  the  hepatic  cells,  and 
which  has  found  its  way  into  the  ramifications  of  the  hepatic  ducts, 
may  be  directly  conveyed  by  the  trunk  of  the  latter  into  the  intestine, 
or  it  may  regurgitate  along  the  cystic  duct  into  the  gall-bladder.  It 
is  probable  that  the  secreting  process  is  constantly  going  on ;  although, 
as  in  other  cases,  it  may  vary  in  its  degree  of  activity  at  different  times. 
"When  the  process  of  digestion  is  taking  place,  and  the  small  intestine 
is  filled  with  chyme,  there  is  probably  an  uninterrupted  flow  of  bile  into 
its  cavity ;  but  when  the  intestine  is  empty,  the  bile  seems  not  to  be 
admitted  into  it,  but  rather  to  flow  back  into  the  gall-bladder,  in  which 
it  is  stored  up  as  in  a  reservoir,  until  the  time  when  it  may  be  needed. 
In  this  reservoir  it  undergoes  a  certain  degree  of  concentration,  by  the 
absorption  of  its  watery  part ;  and  it  also  becomes  mixed  with  a  large 
proportion  of  mucus,  which  is  secreted  by  the  walls  of  the  gall-bladder. 
— As  the  analyses  of  Bile  have  been  chiefly  made  upon  the  fluid  ob- 
tained from  this  receptacle,  they  probably  over-estimate  the  proportion 
of  solid  matter  contained  in  this  secretion ;  which  is  usually  stated  at 
from  8  to  9^^  per  cent.  Of  this  solid  matter  about  a  tenth  consists  of 
alkaline  and  earthy  salts,  corresponding  with  those  of  the  blood  ;  whilst 
the  remainder  is  made  up  of  organic  constituents.  These  are  very 
readily  decomposed,  and  enter  into  new  combinations  with  the  sub- 
stances employed  to  separate  them ;  so  that  different  chemists,  by  em- 
ploying different  means  of  analysis,  have  obtained  results  which  seem 
far  from  conformable.  All  are  agreed,  however,  that  the  chief  part 
of  the  solid  ingredients  of  bile  are  allied  \ofat  in  composition ;  con- 
sisting of  a  very  large  proportion  of  carbon  and  hydrogen,  and  of  a 
comparatively  small  amount  of  oxygen  and  azote.  According  to  Dr. 
Kemp,  the  organic  portion  of  ox-bile  may  be  represented  by  the  for- 
mula 48  Carbon,  42  Hydrogen,  13  Oxygen,  and  1  Nitrogen.  This 
substance,  essentially  corresponding  with  the  bilic  acid,  choleic  acid, 
bilin,  picromel,  &c.,  of  different  Chemists,  seems  to  be  a  fatty  acid, 
(§  261),  united  with  soda,  so  as  to  constitute  a  soap.  In  healthy  bile, 
the  proportion  of  Cholesterine  appears  to  be  very  small ;  and  it  is  held 
in  solution  by  the  preceding  ingredient:  but  in  many  disordered  states, 
and  especially  in  disease  of  the  Gall-bladder,  this  element  is  present 
in  much  larger  amount ;  and  it  usually  forms  the  principal,  if  not 
the  sole,  ingredient  in  biliary  concretions.     It  is  a  white  crystalizable 


\ 


PURPOSES  OF  THE  BILIARY  SECRETION.  415 

fatty  matter,  somewhat  resembling  spermaceti,  free  from  taste  and 
odour,  and  composed  almost  entirely  of  carbon  and  hydrogen, — its 
formula  being  36  Carbon,  32  Hydrogen,  and  1  Oxygen. — The  Colour- 
ing matter  of  Bile  is  a  substance  distinct  from  the  preceding;  that  of 
the  Ox  and  other  graminivorous  animals  appears  to  be  identical,  or 
nearly  so,  with  the  Chlorophyll  of  the  leaves  on  which  they  feed ;  but 
that  of  human  bile  seems  to  possess  different  properties,  and  to  be 
derived  from  the  proper  constituents  of  the  blood. 

725.  Regarding  the  destination  and  purposes  of  this  secretion  in  the 
Animal  economy,  the  following  may  be  considered  as  a  tolerably  com- 
plete summary ;  though  it  is  difficult  to  speak  with  precision  on  some 
points ;  since  the  organic  constituents  of  the  Bile  are  liable  to  be  so 
easily  altered  by  various  reagents,  that  they  are  with  difficulty  recog- 
nized. A  portion  of  the  Bile  unquestionably  passes  off,  in  Man  and 
most  other  animals,  with  the  feces.  This  portion,  which  includes  the 
colouring  matter,  is  probably  that  which  would  be  most  injurious,  if 
retained  in  the  blood,  and  is  most  purely  excrementitious.  But  the 
soapy  portion  has  quite  another  destination.  Just  as  ox-gall  is  com- 
monly used  to  remove  grease  spots,  by  its  solvent  power  for  fatty  mat- 
ter, so  does  the  bile  seem  to  act  in  the  living  body,  by  rendering  soluble 
the  fatty  matters  of  the  food,  and  thus  enabling  them  to  be  absorbed  by 
the  lacteals  (§  494).  Hence,  if  the  passage  of  bile  into  the  intestine  be 
prevented  (as  in  the  recent  experiments  of  Schwann)  without  any 
check  to  its  separation  from  the  blood,  the  animals  gradually  lose  their 
plumpness,  and  at  last  die  in  a  state  of  emaciation, — the  fatty  matter 
of  their  food  not  being  introduced  into  their  absorbent  system,  nor  ap- 
plied to  the  maintenance  of  their  respiration.  The  fatty  matter  of  the 
bile,  when  re-absorbed  with  that  of  the  newly-ingested  food,  is  proba- 
bly, like  it,  carried  off  by  the  respiratory  process :  but  it  is  easily  shown, 
that  the  biliary  matter  cannot  supply  more  than  one-sixth  or  one- 
eighth  of  the  amount  of  carbon  eliminated  from  the  lungs  in  the  form 
of  carbonic  acid ;  and  that  it  cannot  be  (as  supposed  by  Liebig)  the 
chief  fuel  of  the  process  of  combustion,  which  is  kept  up  through  the 
agency  of  those  organs. 

726.  The  elements  of  the  Bile  may  be  altogether  supplied  by  the 
disintegration  of  the  tissues;  and  this  must  certainly  be  the  case,  when 
the  amount  of  food  taken  is  no  more  than  enough  to  supply  the  waste 
of  the  system.  We  may  regard  it,  then,  as  one  office  of  the  Liver  to 
remove  from  the  blood  such  products  of  that  disintegration,  as  are  rich 
in  carbon  and  hydrogen.  But  there  can  be  little  doubt,  that  the  Liver 
has  also  for  its  office,  to  draw  off  from  the  blood  any  superfluity  which 
may  exist  in  the  non-azotized  compounds  derived  from  the  food,  be- 
yond the  amount  that  is  requisite  for  the  supply  of  the  respiratory  pro- 
cess, or  that  can  be  deposited  as  fat.  For  we  continually  witness  the 
results  of  habitual  excess  in  the  amount  of  such  sbstances,  in  pro- 
ducing that  state  of  the  system  commonly  termed  bilious;  of  which  all 
the  symptoms  are  referable  to  the  accumulation  of  the  elements  of  the 
bile  from  the  blood,  and  the  consequent  deterioration  in  the  purity  of 


416  COMPARATIVE  STRUCTURE  OP  KIDNEY. 

the  circulating  fluid.  Where  a  tendency  to  such  a  state  exists,  proper 
means  should  be  taken  to  stimulate  the  liver  to  increased  activity ;  but 
the  chief  reliance  should  be  placed  on  the  avoidance  of  those  articles  of 
diet,  which  contain  a  large  proportion  of  non-azotized  matter,  and  on 
abstinence  from  superfluous  nutriment  of  any  description.  That  the 
less  hydro-carbon  separated  from  the  blood  by  Respiration,  the  more  is 
eliminated  from  it  by  the  Biliary  secretion,  seems  to  be  a  general  prin- 
ciple throughout  the  Animal  kingdom ;  the  Liver  and  Respiratory 
organs  bearing,  almost  everywhere,  an  inverse  ratio  to  each  other  in 
their  degree  of.  development. 

3.   Of  the  Kidneys  and  the  Urinary  Excretion, 

727.  The  Kidneys  are  perhaps  the  most  purely  excreting  organs  in 
the  body;   their  function  being  to  separate  from  the  Blood  certain 
matters  that  would  be  injurious  to  it  if  retained ;  and  these  matters 
being  destined  to  immediate  and  complete  re- 
Fig^ii9.  moval  from  the  system.     We  have  seen  that, 

in  the  Lungs,  the  excretion  of  Carbonic  acid 
is  made  subservient  to  the  absorption  of  Oxy- 
gen ;  and  the  separation  of  a  fatty  acid  from 
the  blood,  which  is  effected  by  the  Liver,  is  a 
means  of  introducing  a  new  supply  of  fatty 
matter  into  the  system.  There  is  no  ulterior 
purpose  of  this  kind  in  the  secreting  action  of 
the  Kidney;  the  product  of  which  is  invari- 
ably conveyed  directly  to  an  outlet,  by  which 
it  may  be  discharged  from  the  body.  Some 
traces  of  Urinary  organs  may  be  detected  in 

Embryo  of  Green  Lizard:-  ^^^^  ^^  ^hc  higher  luVCrtebrata  ;  but  it  is  in 
a,  heart;  6,  duplex  aorta;  c,  FishcS,  that  they  first  prCSCUt  a  Considerable  de- 
vena  cava;    d,  intestine;    e,  ,  '        ,  %  .  ^  ,.  ,,  i     Ji       it 

liver;/,  rudiment  of  Wolffian  vclopmeut ;  ancl  lu  ascendmg  through  the  Ver- 
Siiifs/'  '"'^''"'"''  °' '''"  tebrated  series,  we  find  them  rapidly  increasing 
in  the  complexity  of  their  organization,  and  in 
their  functional  importance,  although  their  size  and  extent  are  not  so 
great.  In  Fishes  the  Kidneys  very  commonly  extend  the  whole 
length  of  the  abdomen  ;  and  they  consist  of  tufts  of  uniform  sized 
tubules,  which  shoot  out  transversely  at  intervals  from  the  long  ure- 
ter, and  which  are  connected  together  by  a  loose  w^eb  of  areolar  tis- 
sue, that  supports  the  network  of  vessels  distributed  upon  their  walls. 
This  condition  of  the  urinary  organs  is  very  analogous  to  that  of  the 
Corpus  Wolffianum  or  temporary  kidney  of  the  embryo  of  higher  ani- 
mals (Fig.  119,y*).  A  similar  condition  is  found  in  the  true  Kidney 
of  higher  animals  at  an  early  grade  of  development  (as  shown  in  Fig. 
120) ;  the  tubuli  uriniferi  being  short  and  straight.  In  their  more  ad- 
vanced condition,  however,  they  become  long  and  convoluted ;  and 
the  ramifications  of  the  capillary  vessels  come  into  very  close  relation 
with  them  (Fig.  121).   It  is  in  the  higher  Reptiles,  that  we  first  meet 


STRUCTURE  OF  HUMAN  KIDNEY. 


417 


with  the  distinction  between  the  cortical  and  medullary  substance  ; 
the  former  being  the  part  in  which  the  blood-vessels  are  most  copi- 


ng. 120, 


Kidney  of  foetal  Boa :— the  urinary  tubes  as  yet  short  and  straight. 

ously  distributed,  and  in  which  the  tubuli  have  the  most  convoluted 
arrangement ;  and  the  latter  consisting  chiefly  of  straight  tubuli,  con- 
verging towards  the  points  at  which  they  discharge  themselves  into 
the  ureter  (Fig.  122).     The  bundles  of  tubuli  and  their  vascular 


Fig.  121. 


Fig.  122. 


Portion  of  Kidney  from  Coluber :— a,  a,  vascular  trunk ; 
b,  6,  ureter;  c,  c,  converging  fasciculi  of  tubuli  uriniferi. 


Pyramidal  fasciculi  of  tubuli 
uriniferi  of  Bird,  terminating  in 
one  of  the  branches  of  the  ureter. 


plexuses  remain  distinct,  however,  in  Birds  and  in  the  lower  Mam- 
malia, so  as  to  give  to  the  gland  a  lobulated  character;  but  in  the 
Human  Kidney, they  come  into  closer  contact;  and  the  vascular  con- 
nection between  the  plexuses  of  the  different  bundles  is  such,  as  to 
prevent  any  separation  into  distinct  lobules. 

728.  The  act  of  secretion  appears  to  be  effected,  as  in  other  Glands, 
by  the  epithelial  cells  lining  the  tubuli  uriniferi ;  these  cells  drawing 
the  materials  of  their  development  from  the  vascular  plexus  upon  the 
exterior  of  these  tubuli ;  and  delivering  them  up,  when  they  have  com- 
pleted their  own  term  of  existence,  to  be  carried  off  through  the  open 
orifices  of  the  tubuli.  But  the  Kidney  contains  another  apparatus,  of 
a  very  peculiar  description  ;  which  appears  specially  destined  for  the 
separation  of  the  superfluous^wic?  of  the  system.  When  a  section  of 
the  Kidney  is  slightly  magnified  (Fig.  124,  b),  the  cut  surface  is  seen 
to  be  studded  by  a  number  of  little  dark  points  ;  each  one  of  which, 
when  examined  under  a  higher  magnifying  power,  is  found  to  consist 
of  a  knot  of  minute  blood-vessels,  formed  by  the  convolutions  of 
thin-walled  capillaries  (Fig.  125,  m).  According  to  the  recent  inqui- 
ries of  Mr.  Bowman,  each  one  of  these  knots  is  included  in  the 
extremity  of  one  of  tubuli  uriniferi,  which  swells  into  a  flask-like 
capsular  dilatation  to  receive  it.  Each  of  these  vascular  tufts  (called 
27 


418 


CIRCULATION  IN  THE  KIDNEY. 


Malpighian  bodies,  after  their  discoverer),  is  directly  supplied  by  a 
branch  of  the  renal  artery  (Fig.  125,  af) ;  which,  upon  piercing  the 


Fig. 123. 


Fig.  125. 


Portion  of  the  Kidney 
of  a  new-born  infant,  a, 
natural  size ;  1,  1.  Cor- 
pora Malpighiana,  as 
dispersed  points  in  the 
cortical  substance ;  2, 
papilla.  B,  a  smaller 
part  magnified ;  1, 1,  Cor- 
pora Malpighiana ;  2,  2, 
tubuli  urinifcri. 


Distribution  of  the  Renal  ves- 
sels ;  from  Kidney  of  Horse :— a, 
branch  of  Renal  artery ;  a/, 
afferent  vessel ;  m,  m,  Malpigh- 
ian tufts  ;  €/,  e/,  efferent  vessels; 
j7,  vascular  plexus  surrounding 
the  tubes ;  s/,  straight  tube ;  ci, 
convoluted  tube.  Magnified 
about  30  diameters. 


A  section  of  the  Kidney,  sur- 
mounted by  the  supra-renal  cap- 
sule; the  swellings  upon  the  surface 
mark  the  original  constitution  of 
the  organ,  as  made  up  of  distinct 
lobes.  1.  The  supra-renal  capsule. 
2.  The  vascular  portion  of  the  kid- 
ney. 3,  3.  Its  tubular  portion,  con- 
sisting of  cones.  4,  4.  Two  of  the 
papilla3  projecting  into  their  cor- 
responding calices.  5,  5,  5.  The 
ihree  infundibula;  the  middle  5  is 
situated  in  the  mouth  of  a  calyx.  6. 
The  pelvis.    7.  The  ureter. 

capsule,  subdivides  into  a  group  of  capillaries ;  and  these,  after  form- 
ing the  convoluted  tuft,  coalesce  into  a  single  efferent  trunk  (e/*), 
which  may  be  considered  as  representing  (in  a  small  way)  the  vena 
portse.  For  the  efferent  trunks  of  the  Malpighian  bodies  discharge 
their  blood  into  the  capillary  plexus,  which  surrounds  the  tubuli 
uriniferi,  and  from  which  the  solid  matter  of  the  urinary  secretion  is 
elaborated  ;  just  as  the  vena  portse  supplies  the  capillary  plexus,  from 
which  the  biliary  secretion  is  elaborated  in  the  liver.  The  special 
purpose  of  the  Malpighian  bodies  appears  to  be,  to  allow  of  the  trans- 
udation of  the  water  of  the  blood,  which  is  filtered  off  (so  to  speak) 
through  the  thin  walls  of  their  capillaries,  and  thus  passes  into  the 
tubuli  uriniferi.  It  is  well  known  that  the  fluid  and  solid  constituents 
of  the  urinary  secretion  bear  no  constant  relation  to  each  other ;  the 
amount  of  fluid  depending  mainly  upon  the  degree  of  fullness  of  the 
blood-vessels ;  whilst  the  amount  of  solid  matter  is  governed,  as  we 
shall  presently  see,  by  the  previous  waste  of  the  tissues.  The  quan- 
tity of  fluid  in  the  blood-vessels  is  governed  by  the  relative  amount 
that  has  been  absorbed,  and  that  which  has  been  exhaled  from  the 
skin  ;  so  that  the  quantity  to  be  drawn  off  by  the  Kidneys  is  increased, 
either  by  augmented  absorption,  or  by  diminished  exhalation.     The 


CHARACTERS  OF  THE  URINARY  EXCRETION.  419 

Malpighian  bodies  seem  to  act  the  part  of  a  system  of  regulating 
valves  ;  permitting  the  transudation  of  only  enough  fluid  to  dissolve 
the  solid  matter,  when  there  is  no  superfluity  of  water  in  the  vessels ; 
but  allowing  the  escape  of  an  almost  unlimited  amount  of  it,  when 
increased  imbibition  has  rendered  the  vessels  unusually  turgid. 

729.  The  average  amount  of  Urine  excreted  in  twenty-four  hours, 
by  adults  who  do  not  drink  more  than  the  wants  of  nature  require,  is 
probably  from  30  to  40  oz.  ;  and  its  average  specific  gravity  may  be 
about  1020.  The  quantity  of  fluid  is  usually  less,  and  the  specific 
gravity  of  the  secretion  consequently  greater  in  summer  than  in  win- 
ter ;  on  account  of  the  larger  proportion  of  fluid  exhaled  by  the  skin 
during  the  former  season.  The  quantity  of  solid  matter  has  been  found 
to  vary,  within  the  limits  of  ordinary  health,  from  3*6  to  6-7  per  cent.; 
and  the  extent  of  variation  in  disease  is  doubtless  much  greater. 
About  one-third  of  the  solid  matter  is  made  up  of  alkaline  and  earthy 
salts;  and  the  remainder  is  made  up  of  organic  compounds.  The 
salts  are  partly  those  of  the  blood,  which  will  not  be  separated  during 
the  transudation  of  the  serum  through  the  membranous  walls  of  the 
Malpighian  capillaries,  although  the  albuminous  matter  is  kept  back 
(§  196).  But  there  is  a  much  larger  proportion  of  the  alkaline  and 
earthy  phosphates  in  the  urine,  than  is  present  in  the  blood  ;  and  this 
is  liable  to  a  further  increase  under  circumstances  to  be  presently 
alluded  to. 

730.  The  organic  compounds  present  in  the  Urinary  secretion  (in 
its  healthy  state  at  least),  are  undoubtedly  the  result  of  the  waste  or 
disintegration  of  the  animal  fabric;  as  well  as  (in  certain  cases)  of  the 
decomposition  of  constituents  of  the  blood,  which  have  never  under- 
gone conversion  into  organized  tissue.  Their  unfitness  to  be  retained 
within  the  system,  is  proved  by  the  fatal  results  which  speedily  ensue, 
when  their  elimination  by  the  secreting  process  receives  a  check;  and 
also  by  the  crystaline  form,  in  which  the  most  characteristic  of  them 
present  themselves, — such  a  form  being  altogether  incompatible  with 
the  possession  of  plastic  or  organizable  properties.  Of  these  com- 
pounds, the  most  important,  in  Man,  is  that  which  is  named  Urea. 
It  exists  in  Urine  in  a  state  of  perfect  solution  ;  and  may  be  readily 
separated  from  it  in  the  form  of  transparent  colourless  crystals,  which 
have  a  faint  and  peculiar  but  not  urinous  odour.  In  its  ultimate 
composition  it  is  identical  with  Cyanate  of  Ammonia,  being  made  up 
of  2  Carbon,  4  Hydrogen,  2  Nitrogen,  and  2  Oxygen, — a  formula 
much  more  simple  than  that  of  almost  any  other  organic  substance. 
If  we  compare  its  composition  with  that  of  Proteine,  we  shall  find  that 
it  contains  a  far  larger  proportion  of  Nitrogen,  and  far  less  Carbon 
and  Hydrogen.  Thus,  making  Oxygen  the  standard  of  comparison, 
we  find  that 

1  Equivalent  of  Proteine  contains  40  C,  31  H,    5  N,  12  0. 
6  Equivalents  of  Urea  contain        12  C,  24  H,  12  N,  12  O. 

731.  Hence  it  seems  evident,  that  the  great  purpose  of  the  Urinary 


420  UREA,  AND  URIC  ACID. 

excretion  is  to  carry  off  those  products  of  the  metamorphosis  of  the 
azotized  tissues,  which  can  neither  be  set  free  in  the  condition  of  car- 
bonic acid  and  water  through  the  lungs,  nor  got  rid  of  by  the  agency 
of  the  liver  in  the  form  of  solid  biliary  matter.  The  amount  of  Urea 
in  the  Urine  is  liable  to  very  great  variation,  in  accordance  with  the 
degree  in  which  the  disintegrating  process  has  been  taking  place  in 
the  solid  fabric ;  and  also  in  conformity  with  the  amount  of  azotized 
matter,  which  has  been  taken  in  as  food.  Supposing  that  the  latter 
were  so  precisely  adjusted  to  the  wants  of  the  system,  as  to  supply 
only  that  which  is  required  for  its  maintenance,  w^e  might  then  mea- 
sure the  amount  of  previous  waste,  by  the  quantity  of  Urea  present 
in  the  Urine.  There  can  be  no  doubt  as  to  the  fact,  that,  other  things 
being  equal,  the  amount  of  Urea  is  greatly  increased  by  any  unusual 
exertion  of  the  Muscular  system  ;  but  such  an  increase  cannot  be  in- 
variably, or  even  usually,  attributed  to  this  cause ;  since  it  is  equally 
certain,  that  any  superfluity  in  the  amount  of  azotized  matter  received 
into  the  blood,  must  be  drawn  off  by  the  urinary  excretion,  and  thus 
that  an  increase  in  the  quantity  of  urea  may  be  occasioned  by  an  ex- 
cessive use  of  proteine-compounds  as  articles  of  food.  The  average 
proportion  of  Urea,  under  ordinary  circumstances  as  to  diet  and  exer- 
cise, seems  to  be  from  20  to  35  parts  in  1000  ;  but  it  may  be  raised 
to  45  parts  by  violent  exercise,  and  to  53  parts  by  an  exclusively  ani- 
mal diet ;  whilst  it  may  fall  as  low  as  from  12  to  15  parts,  when  the 
dijet  is  deficient  in  azotized  matter.  The  total  daily  excretion  of  Urea 
in  adult  males  seems  to  average  about  430  grains,  and  that  of  females 
nearly  300  grains;  but  these  averages  may  be  widely  departed  from, 
on  the  side  either  of  excess  or  diminution,  according  to  the  circum- 
stances already  noticed.  It  is  interesting  to  observe,  that  children  of 
eight  years  old  excrete,  on  the  average,  half  qs  much  Urea  as  adults; 
whilst,  in  very  old  persons,  the  quantity  sinks  to  one-third,  or  even 
less.  In  proportion  to  their  relative  bulks,  therefore,  children  excrete 
at  least  two  or  three  times  the  quantity  of  urea,  that  is  set  free  by 
adults  ;  and  four  or  five  times  that  which  is  excreted  by  old  persons; 
— a  fact  which  corresponds  with  other  indications  of  the  far  greater 
rapidity  of  interstitial  change  in  the  earlier  periods  of  life,  than  in 
adult  or  advanced  age. 

732.  There  is  an  organic  compound,  nearly  allied  to  Urea  in  com- 
position, but  differing  from  it  in  its  distinctly  acid  properties,  and  also 
in  its  com>parative  insolubility.  This  substance,  termed  Uric  or  Lithic 
Acid,  forms  but  a  small  proportion  of  the  solid  matter  of  Human 
Urine  in  the  state  of  health  ;  but  it  is  the  chief  element  in  the  Urine 
of  the  lower  Vertebrata;  and  its  presence  in  too  large  a  proportion  is 
a  frequent  source  of  disease  in  Man.  Its  ultimate  composition  is 
10  Carbon,  4  Hydrogen,  4  Nitrogen,  6  Oxygen;  it  crystalizes  in 
fine  scales  of  a  brilliant  white  colour  and  silky  lustre  ;  and  it  is  so 
sparingly  soluble  in  water,  that  at  least  10,000  times  its  own  weight 
of  fluid  is  required  to  dissolve  it.  In  healthy  Human  urine,  it  is  in  a 
state  of  perfect  solution;  but  it  is  precipitated  immediately  on  the  ad- 


URIC  AND  HIPPURIC  ACIDS.  421 

dition  of  a  small  quantity  of  any  acid,  even  the  Carbonic:  it  is  evi- 
dent, therefore,  that  it  is  held  in  solution  by  union  with  some  base ; 
and  according  to  Liebig,  this  base  is  Soda,  obtained  from  the  bibasic 
Phosphate  of  Soda,  which  is  present  in  the  urine,  and  which,  by 
yielding  up  a  part  of  its  base,  gives  the  acid  reaction  that  is  charac- 
teristic of  the  fluid  in  a  healthy  state.  It  is  not  unfrequently  seen, 
that  the  Urine,  although  clear  when  voided,  deposits  Lithic  acid  when 
it  is  cooled;  and  this  deposit  may  be  due  either  to  the  presence  of 
more  Lithic  acid  than  the  Phosphate  of  Soda  can  take  up  when  cold; 
or  to  the  presence  of  some  other  acids  in  the  Urine,  which  set  free  the 
Lithic  acid,  when  the  solvent  power  of  the  Phosphate  is  diminished 
by  the  depressed  temperature. 

733.  The  amount  of  Uric  acid  in  healthy  Urine  does  not  seem  to 
be  much  influenced  by  the  diet,  or  by  the  w^aste  of  the  tissues;  never 
varying  much,  either  by  excess  or  diminution,  from  1  part  in  1000. 
It  is  liable,  however,  to  be  greatly  increased  in  certain  disordered 
states  of  the  system  ;  and  the  surplus,  not  being  kept  in  solution  by 
the  Phosphate  of  Soda,  is  deposited  as  a  sediment,  which  usually  has 
a  crystaline  character,  and  is  tinged  of  a  reddish  hue  by  the  colour- 
ing matter  of  the  urine.  Not  unfrequently  the  Uric  acid  is  deposited 
in  combination  with  an  alkaline  base;  and  the  colour  of  the  sediment 
is  then  usually  of  a  brick-red.  Such  depositions  may  take  place 
directly  from  the  blood  ;  thus,  in  attacks  of  Gout,  urate  of  soda  is 
separated  from  the  circulating  blood,  and  is  deposited  in  the  tissues 
around  the  affected  joints,  forming  the  concretions  termed  "  chalk- 
stones."  There  can  be  no  doubt  that,  when  there  is  a  positive  ex- 
cess of  Uric  acid  in  the  Urine,  it  may  be  generally  reduced  by  dimin- 
ishing the  quantity  of  azotized  matter  in  the  food  ;  but  when  the 
deposit  is  consequent  upon  the  presence  of  some  other  acid  in  the 
urine,  our  treatment  should  be  rather  directed  to  the  neutralization  of 
this,  or  to  the  prevention  of  its  formation. 

734.  There  seems  reason  to  believe  that  we  are  to  regard  Hippuric 
acid  as  a  normal  element  of  the  Urine  of  Man,  although  it  has  been 
usually  supposed  to  be  restricted  to  the  Herbivorous  quadrupeds, 
"where  it  replaces  Uric  Acid.  Its  composition  and  properties  are  very 
different  from  those  of  that  substance.  When  pure,  it  forms  long 
transparent  four-sided  prisms;  it  is  soluble  in  400  parts  of  cold  water, 
and  dissolves  readily  at  a  boiling  heat;  and  it  has  a  strong  acid  reac- 
tion, with  a  bitterish  taste.  It  is  composed  of  18  Carbon,  8  Hydro- 
gen, 1  Nitrogen,  and  5  Oxygen,  w^ith  1  equiv.  of  Water.  When 
exposed  to  a  high  temperature,  or  subjected  to  the  putrefactive  pro- 
cess, it  is  partly  converted  into  Benzoic  acid  ;  and  it  is  on  the  presence 
of  the  latter  in  putrefied  Human  Urine,  that  the  belief  in  the  existence 
of  Hippuric  acid  in  the  same  fluid  w^hen  fresh,  is  chiefly  grounded. 
It  is  a  curious  fact,  that  the  administration  of  Benzoic  acid  causes 
the  appearance  of  a  large  additional  quantity  of  Hippuric  acid  in  the 
Urine;  so  that  its  presence  is  then  sufficiently  evident.  This  fact  has 
been  applied  to  the  treatment  of  disease ;  for  as  the  salts  of  Hippuric 


422  OTHER  CONSTITUENTS  OF  URINE. 

acid  are  much  more  soluble  than  those  of  Lithic  acid,  it  is  obviously 
advantageous  to  cause  the  effete  crystaline  matters,  which  are  de- 
stined for  elimination  from  the  system,  to  be  discharged  as  soluble 
Hippurates,  rather  than  to  be  deposited  as  insoluble  Lithates;  and  it 
is  asserted  by  Mr.  A.  Ure,  that  he  has  succeeded,  by  the  administra- 
tion of  Benzoic  acid,  in  preventing  the  deposition  of  Gouty  concre- 
tions, and  even  in  removing  them  when  they. had  been  formed. 

735.  Another  acid  has  usually  been  regarded,  until  recently,  as 
one  of  the  regular  constituents  of  healthy  urine,  and  as*  liable  to  un- 
dergo a  considerable  increase  in  disease.  This  is  the  Lactic;  an  acid 
which  is  readily  formed  in  Milk,  by  the  metamorphosis  of  its  saccha- 
rine elements.  But  it  seems  doubtful,  from  the  recent  inquiries  of 
Liebig,  whether  we  are  to  admit  it  as  a  regular  constituent  of  healthy 
human  Urine;  and  it  appears  that  a  peculiar  azotized  compound, 
which  is  not  entitled  to  the  designation  of  an  acid,  but  which  forms 
a  definite  combination  with  Zinc,  has  been  mistaken  for  it.  The 
amount  of  this  azotized  product,  and  of  the  compounds  it  forms 
(usually  designated  as  lactic  acid  and  the  lactates),  has  been  found 
to  undergo  considerable  increase,  when  the  food  ingested  was  alto- 
gether destitute  of  azote,  and  when  the  proportion  of  urea  was  the 
smallest.  It  would  seem  as  if  some  of  the  azotized  matter,  result- 
ing from  the  disintegration  of  the  tissues,  was  then  discharged  in 
this  form,  rather  than  in  that  of  the  more  highly  azotized  compound, 
urea. 

736.  Of  the  substances  ranked  under  the  head  of  Extractive  Mat- 
ters, very  little  is  definitely  known.  They  seem  to  consist,  for  the 
most  part,  of  non-azotized  compounds  in  a  state  of  change ;  and  their 
usual  proportion,  which  is  about  10  parts  in  1000,  has  been  found  to 
increase  to  16J  parts  when  the  diet  was  exclusively  vegetable,  and 
to  diminish  to  5  parts  when  only  animal  food  was  ingested. 

737.  The  Urine  also  contains  a  considerable  amount  of  Saline 
matter,  of  which  the  acids  as  well  as  the  bases  are  derived  from  the 
mineral  kingdom  ;  and  the  excretion  of  them,  after  they  have  served 
their  purpose  in  the  economy,  appears  to  be  one  of  the  chief  functions 
of  the  Kidney.  Of  these,  a  part  may  find  their  way  directly  into  the 
urine  from  the  serum  of  the  blood,  when  its  water  is  being  filtered  off 
(so  to  speak)  through  the  walls  of  the  Malpighian  capillaries  ;  for 
although,  from  the  peculiar  properties  of  animal  membranes  (§  196), 
the  albuminous  constituents  of  the  serum  are  held  back,  the  saline 
matter,  which  is  in  a  state  of  perfect  solution,  must  pass  with  the 
water.  This  is  probably  the  chief  source  of  the  large  quantity  of  the 
muriates  of  soda  and  ammonia  contained  in  the  urine.  But  the 
Urinary  secretion  seems  to  be  specially  destined  to  eliminate  the  saline 
compounds,  which  are  formed  by  the  acidification  of  the  Sulphur  and 
Phosphorus,  taken  in  with  the  proteine-compounds  as  food.  These 
substances  are  united  with  Oxygen  in  the  system,  and  are  thus  con- 
verted into  Sulphuric  and  Phosphoric  acids;  w^hich  acids  unite  with 
alkaline  bases,  that  were  ingested  in  combination  with  Citric,  Tartaric, 


» 


SALTS  OF  THE  URINE.  423 

Oxalic,  and  other  organic  acids;  the  latter  undergoing  decomposition 
within  the  system,  and  leaving  the  bases  ready  to  unite  with  others. 
Such  weakly  combined  bases  abound  in  the  food  of  Herbivorous  ani- 
mals ;  and  their  urine  is  almost  invariably  alkaline^  the  quantity  of  the 
Sulphuric  and  Phosphoric  acids  generated  in  the  system  not  being 
sufficient  to  neutralize  it.  On  the  other  hand,  they  are  nearly  absent 
in  the  food  of  the  Carnivora;  and  their  urine  is  therefore  almost  inva- 
riably acid^  from  the  want  of  neutralization  of  the  Sulphuric  and 
Phosphoric  acids. 

738.  The  Alkaline  Sulphates^  whether  taken  in  as  such,  or  formed 
in  the  manner  now  described,  are  soluble  enough  to  be  always  passed 
off  in  a  fluid  form  ;  but  this  is  not  uniformly  the  case  with  the  Phos- 
phates,  which  are  frequently  deposited  as  sediments  of  a  dead-white 
aspect,  sometimes  crystaline,  and  sometimes  wholly  or  partly  amor- 
phous. The  crystaline  sediment  consists  of  the  triple  phosphate,  or 
phosphate  of  ammonia  and  magnesia ;  the  amorphous  contains  an  ad- 
mixture of  the  phosphate  of  lime.  The  urine,  when  these  are  depo- 
sited, is  usually  alkaline,  sometimes  very  decidedly  so ;  and  there  is 
reason  to  think  that,  in  many  cases,  this  alkaline  character,  and  the 
deposit  of  phosphatic  sediments,  are  due  to  an  alkaline  secretion  from 
the  walls  of  the  bladder  and  urinary  passages,  which  result  from  an 
irritable  state  nf  their  membrane, — the  urine,  as  secreted  by  the  kid- 
ney, having  its  usual  properties.*  That  an  alkaline  condition  of  the 
urine,  resulting  from  the  presence  of  an  unusual  amount  of  bases,  is 
capable  of  producing  a  phosphatic  deposit,  is  shown  by  the  simple 
experiment  of  adding  ammonia  to  healthy  urine,  which  will  occasion 
a  precipitation  of  the  triple  phosphate. 

739.  But  there  can  be  little  doubt,  that  a  frequent  cause  of  the 
deposit  is  excessive  production  of  the  phosphatic  salts,  arising  from 
the  increased  waste  or  disintegration  of  Nervous  matter,  which  takes 
place  when  it  is  in  a  state  of  unusual  activity,  either  from  intense 
thought,  from  prolonged  exertion,  or  from  continued  anxiety.  The 
general  principles  already  set  forth,  in  regard  to  the  dependence  of 
the  functional  activity  of  the  Nervous  Centres  upon  a  supply  of  arte- 
rialized  blood  (§  384),  show  the  probability  that  every  act  of  theirs 
involves  the  oxygenation  of  a  certain  quantity  of  nervous  matter.  In 
this  oxygenation,  phosphoric  acid  will  be  produced,  from  the  large 
amount  of  phosphorus  contained  in  the  nervous  matter  ;  and  this  will 
unite  in  part  with  ammonia,  which  is  perhaps  set  free  by  the  same 
metamorphosis,  or  is  derived  from  other  sources;  and  in  part  with 
bases  derived  from  the  food.  The  experience  of  every  studious  man 
must  have  shown  him  (if  he  make  any  observations  on  the  matter  at 
all)  the  frequent  coincidence  between  the  presence  of  phosphatic 
deposits  in  his  urine,  and  an  excess  of  mental  labour ;  and  there  are 
many  instances  on  record,  in  which  the  periodical  recurrence  of  the 

*  See  Dr.  G.  O.  Rees  on  the  Analysis  of  the  Blood  and  Urine  in  Health  and  Dis- 
ease, 2d  Ed.  p.  136. 


424  DISORDERED  STATES  OF  THE  URINARY  SECRETION. 

latter  has  been  so  invariably  followed  by  the  recurrence  of  the  former, 
that  no  reasonable  doubt  can  exist  as  to  their  mutual  connection. 

740.  It  is  very  important,  for  the  successful  treatment  of  those 
Urinary  deposits,  which  consist  of  the  normal  elements  of  the  Urine, 
— namely,  Lithic  Acid,  and  the  Phosphates, — that  the  leading  facts 
already  stated  should  be  borne  continually  in  mind.  In  the  first  place, 
these  sediments  may  depend  upon  the  general  condition  of  the  fluid, 
and  not  upon  any  excess  in  the  constituents  of  which  they  are  com- 
posed ;  thus  a  lithic  deposit  may  result  from  the  presence  of  an  excess 
of  some  other  acid  in  the  urine ;  and  a  phosphatic  sediment  may  be 
produced  by  the  excess  of  bases.  In  such  cases,  then,  our  treatment 
should  be  directed,  not  to  diminish  the  quantity  of  the  peculiar  con- 
stituents of  the  deposits,  but  to  rectify  the  state  of  the  Urine  on  which 
their  precipitation  depends.  But,  in  the  second  place,  the  sediments 
may  be  present  in  such  great  amount,  as  to  indicate  that  their  consti- 
tuents are  present  in  the  urine  to  an  excessive  degree  ;  and  our  treat- 
ment must  then  be  directed  towards  the  diminution  of  the  quantity 
produced.  Thus  the  tendency  to  lithic  acid  deposit  may  be  frequently 
cured,  by  simply  diminishing  the  quantity  of  azotized  matter  in  the 
food  ;  and  the  undue  formation  of  the  phosphates  may  be  often  kept 
in  check  by  that  mental  repose,  which  is  peculiarly  required  after 
long-continued  and  severe  exercise  of  the  intellectual  faculties,  or 
strong  excitement  of  the  feelings. 

741.  There  is  no  doubt  whatever,  that  the  total  suspension  of  the 
Urinary  secretion  is  productive  of  rapidly  fatal  results,  from  the  accu- 
mulation of  the  elements  of  the  secretion  in  the  blood ;  and  it  would 
appear  that  the  tissue  on  which  their  presence  in  the  circulating  fluid 
exerts  the  most  injurious  effects,  is  the  Nervous.  It  is  probable  that 
Urea  is  the  substance,  which  is  most  directly  concerned  in  producing 
the  noxious  influence  ;  and  we  see  an  effort  made  by  the  system  (so  to 
speak)  to  get  rid  of  it,  in  those  cases  in  which  a  discharge  of  urinous 
fluid  takes  place  by  unusual  channels,  such  as  from  the  mucous  mem- 
brane of  the  stomach,  the  mamma,  the  umbilicus,  the  nose,&c.,  w^hen 
the  usual  secreting  action  of  the  Kidney  has  been  suspended.  Al- 
though the  accounts  of  such  cases  have  been  treated  w^th  ridicule  by 
some  Physiologists,  yet  there  seems  no  valid  reason  to  discredit  them, 
when  it  is  borne  in  mind  that,  in  persons  who  have  died  from  the 
complete  suspension  of  the  secretion,  effusions  containing  urea  have 
been  found  in  the  serous  cavities  of  the  trunk,  and  in  the  ventricles  of 
the  brain.  The  poisonous  influence  of  an  accumulation  of  urea  in  the 
blood,  when  strongly  exerted,  produces,  in  the  first  instance,  irregular 
or  convulsive  movements,  which  are  dependent  upon  irritation  of  the 
Spinal  system  of  nerves;  then  loss  of  consciousness,  depending  upon 
the  suspension  of  the  powers  of  the  Brain  ;  and,  lastly,  complete  sus- 
pension of  the  powers  of  the  spinal  system,  so  that  the  ordinary  reflex 
actions  cease,  and  life  becomes  extinct  from  the  stoppage  of  the  re- 
spiratory movements  (§  688).  There  is  reason  to  believe  that  many 
convulsive  motions,  for  which  no  obvious  cause  can  be  assigned,  have 


CUTANEOUS  GLANDULE. 


425 


their  origin  in  a  disordered  condition  of  the  blood,  resulting  from  im- 
perfect elimination  of  Urea;  thus  it  has  been  ascertained  that,  in  seve- 
ral cases  of  puerperal  convulsions,  urea  was  present  in  the  blood  ;  the 
functional  power  of  the  kidney  being  diminished  by  chronic  disease. 
It  is  especially  to  be  noticed,  that  most  of  the  cases  in  which  the 
urinary  secretion  is  discharged  through  some  irregular  channel,  occur 
in  persons  who  have  been  subject  to  those  convulsive  affections,  which 
are  commonly  designated  as  hysterical;  and  that  the  discharge  of  a  large 
quantity  of  urine  through  the  natural  channel,  is  often  the  termination 
of  an  hysterical  paroxysm.  It  is  desirable,  therefore,  that  in  all  such 
obscure  cases,  the  state  of  the  urinary  secretion  should  be  carefully 
looked  to. 


Fig.  126. 


I 


4.   Of  the  Cutaneous  and  Intestinal  Glandulce. 

742.  The  Glandulae  which  are  disposed  in  the  substance  of  the 
Skin,  and  in  the  walls  of  the  Intestinal  canal,  although  individually, 
minute,  make  up  by  their  aggregation  an  excreting  apparatus  of  no 
mean  importance.     The    Skin  is 

the  seat  of  two  processes  in  parti- 
cular ;  one  of  which  is  destined  to 
free  the  blood  of  a  large  quantity 
of  fluid  ;  and  the  other  to  draw 
off  a  considerable  amount  of  solid 
matter.  To  effect  these  processes, 
w^e  meet  with  two  distinct  classes 
of  glandulae  in  its  substance  ;  the 
Sudoriparous  or  sweat-glands ; 
and  the  Sebaceous  or  oil-glands. 
They  are  both  formed,  however, 
upon  the  same  simple  plan ;  and 
can  frequently  be  distinguished 
only  by  the  nature  of  their  secreted 
product. 

743.  The  Sudoriparous  or  per- 
spiratory glandules  form  small  oval 
or  globular  masses,  situated  just 
beneath  the  cutis,  in  almost  every 
part  of  the  surface  of  the  body. 
Each  is  formed  by  the  convolu- 
tion of  a  single  tube;  which  thence 
runs  towards  the  surface  as  the 
efferent  duct,  making  numerous 
spiral  turns  in  its  passage  through 
the  skin,  and  penetrating  the  epi- 
dermis rather  obliquely,  so  that  its 
orifice  is  covered  by  a  sort  of  little 
valve  of  scarf-skin,  which  is  lifted 


The  anatomy  of  the  skin.  1.  The  epidermis, 
showing  the  oblique  laminae  of  which  it  is  com- 
posedj  and  the  imbricated  disposition  of  the  ridges 
upon  Us  surface.  2.  The  rete  mucosum  or  deep 
layer  of  the  epidermis  3.  Two  of  the  quadrila- 
teral papillary  clumps,  such  as  are  seen  in  the 
palm  of  the  hand  or  sole  of  the  foot;  they  are 
composed  of  minute  conical  papillae.  4.  The 
deep  layer  of  the  cutis,  the  corium.  5.  Adipose 
cells.  6.  A  sudoriparous  gland  with  its  spiral 
duct,  such  as  is  seen  in  the  palm  of  the  hand  or 
sole  of  the  foot.  7.  Another  sudoriparous  gland 
with  a  straighter  duct,  such  as  are  seen  in  the 
scalp.  8.  Two  hairs  from  the  scalp,  enclosed  in 
their  follicles;  their  relative  depth  in  the  skin  is 
preserved.  9.  A  pair  of  sel)aceous  glands,  open- 
ing by  short  ducts  into  the  follicle  of  the  hair. 


426 


VARIATIONS  IN  CUTANEOUS  EXHALATION. 


up  as  the  fluid  issues  from  it.  The  convoluted  knot,  of  which  the 
gland  consists,  is  copiously  supplied  with  blood-vessels.  On  the 
palm  of  the  hand,  the  sole  of  the  foot,  and  the  extremities  of  the 
fingers,  the  apertures  of  the  perspiratory  ducts  are  visible  to  the  naked 
eye,  being  situated  at  regular  distances  along  the  little  ridges  of  sen- 
sory papillae,  and  giving  to  the  latter  the  appearance  of  being  crossed 
by  transverse  lines.  According  to  Mr.  Erasmus  Wilson,  as  many  as 
3528  of  these  glandulae  exist  in  a  square  inch  of  surface  on  the  palm 
of  the  hand ;  and  as  every  tube,  when  straightened  out,  is  about  a 
quarter  of  an  inch  in  length,  it  follows  that  in  a  square  inch  of  skin 
from  the  palm  of  the  hand  there  exists  a  length  of  tube  equal  to  882 
inches,  or  73J  feet.  The  number  of  glandulse  in  other  parts  of  the 
skin  is  sometimes  greater,  but  generally  less  than  this  ;  and  according 
to  Mr.  Wilson,  about  2800  inches  may  be  taken  as  the  average  num- 
ber of  pores  in  each  square  inch  throughout  the  body.  Now  the 
number  of  square  inches  of  surface,  in  a  man  of  ordinary  stature,  is 
about  2500 ;  the  number  of  pores,  therefore,  is  seven  millions  ;  and 
the  number  of  inches  of  perspiratory  tubing  would  thus  be  1,750,000; 
or  145,833  feet ;  or  48,611  yards  ;  or  nearly  28  miles. 

744.  From  this  extensive  system  of  glandulse,  a  secretion  of  watery 
fluid  is  continually  taking  place;  and  a  considerable  amount  of  solid 
matter  also  is  drawn  off  by  the  epithelium-cells  that  line  the  tubuli. 
Under  ordinary  circumstances,  the  fluid  is  carried  off  in  the  state  of 
vapour,  forming  the  insensible  perspiration ;  and  it  is  only  when  its 
amount  is  considerably  increased,  or  when  the  surrounding  air  is 
already  so  loaded  with  moisture  as  to  be  incapable  of  receiving  more, 
that  the  fluid  remains  in  the  form  of  sensible  perspiration  upon  the  sur- 
face of  the  skin.  It  is  difiicult  to  estimate  the  proportion  of  solid 
matter  contained  in  this  secretion  ;  partly  on  account  of  the  great 
variations  in  the  amount  of  fluid  eliminated  by  the  Sudoriparous 
glands,  which  are  governed  by  the  temperature  of  the  skin ;  and 
partly  because  the  secretion  can  scarcely  be  collected  for  analysis, 
free  from  the  sebaceous  and  other  matters  which  accumulate  on  the 
surface  of  the  skin.  According  to  Anselmino  it  varies  from  \  to  IJ 
per  cent.;  and  consists  in  part  of  lactic  acid,  to  which  the  acid  reac- 
tion and  sour  smell  of  the  secretion  are  due ;  in  part  of  a  proteine- 
compound,  which  is  probably  furnished  by  the  epithelium-cells  that 
line  the  tubes  ;  and  in  part  of  saline  matters,  directly  proceeding  from 
the  serum  of  the  blood. 

745.  The  amount  of  fluid  excreted  from  the  skin  is  almost  entirely 
dependent  upon  the  temperature  of  the  surrounding  medium ;  being 
increased  with  its  rise,  and  diminished  with  its  fall.  The  object  of 
this  variation  is  very  evident ;  being  the  regulation  of  the  temperature 
of  the  body.  When  the  surface  is  exposed  to  a  high  degree  of  external 
heat,  the  increased  amount  of  fluid  set  free  from  the  perspiratory 
glands  becomes  the  means  of  keeping  down  its  own  temperature ;  for 
this  fluid  is  then  carried  off  in  a  state  of  vapour,  as  fast  as  it  is  set 
free ;  and  in  its  change  of  form,  it  withdraws  a  large  quantity  of  caloric 


SUPPRESSED  EXHALATION.  ^  427 

from  the  surface.  But  if  the  hot  atmosphere  be  already  loaded  with 
vapour,  this  cooling  power  cannot  be  exerted  ;  the  temperature  of  the 
body  is  raised  ;  and  death  supervenes,  if  the  experiment  be  long  con- 
tinued. The  cause  of  the  increased  secretion  is  probably  to  be  looked 
for  in  the  increased  determination  of  blood  to  the  skin,  which  takes 
place  under  the  stimulus  of  heat. — The  entire  loss  by  Exhalation  from 
the  lungs  and  skin,  during  the  twenty-four  hours,  seems  to  average  a 
little  above  2  lbs.  In  a  warm  dry  atmosphere,  however,  it  has  been 
found  to  rise  to  as  much  as  5  lbs. ;  whilst  in  a  cold  damp  one,  it  may 
be  lowered  to  If  lb.  Of  this  quantity,  the  pulmonary  exhalation  is 
usually  somewhat  less  than  one-third,  and  the  cutaneous  somewhat 
more  than  two-thirds  ;  but  when  the  quantity  of  fluid  lost  is  unusually 
great,  the  increase  must  be  chiefly  in  the  Cutaneous  exhalation  ;  since, 
as  already  pointed  out  (§  701),  the  amount  of  exhalation  from  the 
lungs  is  not  influenced  by  the  external  temperature,  but  only  by  the 
degree  in  which  the  surrounding  air  is  previously  saturated  with 
moisture. 

746.  The  variations  in  the  amount  of  fluid  set  free  by  Cutaneous 
and  Pulmonary  Exhalation,  are  counterbalanced  by  the  regulating 
action  of  the  Kidney ;  which  allows  a  larger  proportion  of  water  to  be 
strained  off  in  a  liquid  state  from  the  blood-vessels,  as  the  Exhalation 
is  less, — and  vice  versa.  The  Cutaneous  and  tJrinary  excretions 
seem  to  be  vicarious,  not  merely  in  regard  to  the  amount  of  fluid 
which  they  carry  off'  from  the  blood ;  but  also  in  respect  to  the  solid 
matter  which  they  eliminate  from  it.  It  appears  that  at  least  100 
grains  of  effete  azotized  matter  are  daily  thrown  off*  from  the  skin ; 
and  any  cause  which  checks  this  excretion,  must  increase  the  labour 
of  the  Kidneys,  or  produce  an  accumulation  of  noxious  matter  in  the 
blood.  Hence  attention  to  the  functions  of  the  skin,  at  all  times  a 
matter  of  great  importance,  is  peculiarly  required  in  the  treatment  of 
Urinary  diseases ;  and  it  will  be  often  found  that  no  means  is  so  useful 
in  removing  the  lithic  acid  deposit,  as  copious  ablution  and  friction 
of  the  skin,  combined  with  exercise.  When  the  Exhalant  action  of 
the  skin  is  completely  checked,  by  the  application  of  an  impermeable 
varnish,  the  eff*ect  is  not  (as  might  be  anticipated)  an  elevation  of  the 
temperature  of  the  body ;  on  the  contrary  it  is  lowered,  in  conse- 
quence, as  it  would  appear,  of  the  interruption  to  the  aeration  of  the 
blood  through  the  skin,  which  is  a  function  of  such  importance  in  the 
lower  animals  (§  671),  and  of  no  trifling  account  in  Man;  and  in  a 
short  time,  a  fatal  result  ensues.  A  partial  suppression  by  the  same 
means  gives  rise  to  febrile  symptoms,  and  to  Albuminuria,  or  escape 
of  the  albuminous  part  of  the  liquor  sanguinis  into  the  urinary  tubes, 
in  consequence  (it  would  appear)  of  the  increased  determination  which 
then  takes  place  towards  the  kidneys.  These  facts  are  interesting,  as 
throwing  light  upon  the  febrile  disturbance,  which  accompanies  those 
cutaneous  diseases,  that  affect  the  whole  surface  of  the  skin  at  once, 
and  interfere  with  its  functions ;  and  as  accounting  also  for  the  Albu- 


J^  SEBACEOUS  GLANDS. 

minuria,  which  frequently  manifests  itself  during  their  progress,  espe- 
cially in  Scarlatina. 

747.  The  Skin  is  likewise  furnished  with  numerous  Sebaceous 
glands,  which  are  distributed  more  or  less  closely  over  the  whole 
surface  of  the  body ;  being  least  abundant  where  the  Perspiratory 
glandulse  are  most  numerous;  and  vice  versa.  They  are  altogether 
absent  on  the  palms  of  the  hands  and  the  soles  of  the  feet ;  and  are 
particularly  frequent  in  the  skin  of  the  face,  and  in  the  scalp.  They 
difier  greatly  in  size  and  in  degree  of  complexity;  sometimes  con- 
sisting of  short  straight  follicles ;  sometimes  closely  resembling  the 
Sudoriparous  glandulse,  the  tubes,  however,  being  usually  straighter 
and  wider;  and  being  sometimes  much  more  complex  in  structure, 
consisting  of  a  number  of  distinct  sacculi  clustered  round  the  extremity 
of  a  common  duct,  into  which  they  open,  and  forming  little  arborescent 
masses,  about  the  size  of  millet  seeds.  In  some  situations  they  ac- 
quire still  greater  complexity.  Thus  the  Meibomian  glandulse,  which 
are  found  at  the  edge  of  the  eyelids,  and  which  secrete  an  unctuous 
matter  for  their  lubrication,  are  long  sacculi  branching  out  at  the  sides 
(Fig.  107);  and  the  glandulse  of  the  ear  passage,  which  secrete  its 
cerumen  or  waxy  matter,  and  which  belong  to  the  general  Sebaceous 
system,  are  formed  of  long  tubes,  highly  contorted,  and  copiously  sup- 
plied with  blood-vessels.  In  the  hairy  parts  of  the  skin,  we  usually 
find  a  pair  of  Sebaceous  follicles  opening  into  the  passage  through 
which  every  hair  ascends  (Fig.  126,  9).  The  purpose  of  the  seba- 
ceous secretion  is  evidently  to  prevent  the  skin  from  being  dried 
and  cracked  by  the  influence  of  the  sun  and  air.  It  is  much  more 
abundant  in  the  races  of  mankind,  which  are  formed  to  exist  in  warm 
climates,  than  in  the  races  that  naturally  inhabit  cold  countries ;  and 
the  former  are  accustomed  to  aid  its  preservative  power,  by  lubri- 
cating their  skin  with  vegetable  oils  of  various  kinds;  which  process 
they  find  to  be  of  use  in  protecting  it  from  the  scorching  influence  of 
the  solar  rays. — The  Sebaceous  follicles  are  frequently  the  residence 
of  a  curious  parasite,  the  Bemodex  folliculorum ;  which  is  stated  by 
Mr.  Erasmus  Wilson  to  be  present  in  great  numbers  in  the  skin  of 
almost  all  inhabitants  of  large  towns ;  the  activity  of  their  cutaneous 
glandular  system  being  much  checked,  by  the  want  of  free  exposure 
to  pure  air,  and  by  inert  habits  of  life. 

748.  To  what  extent  the  Sebaceous  secretion  can  be  regarded  as 
destined  to  free  the  Blood  from  deleterious  matters,  it  may  not,  per- 
haps, be  very  easy  to  say;  but  with  regard  to  the  functions  of  the  skin 
taken  altogether,  as  a  channel  for  the  elimination  of  morbific  matters 
from  the  blood,  it  is  probable  that  they  have  been  much  underrated ; 
and  that  much  more  use  might  be  made  of  it,  in  the  treatment  of  dis- 
eases,— especially  of  such  as  depend  upon  the  presence  of  some  mor- 
bific matter  in  the  circulating  current, — than  is  commonly  thought 
advisable.  We  see  that  Nature  frequently  uses  it  for  this  purpose ;  a 
copious  perspiration  being  often  the  turning-point  or  crisis  of  febrile 
diseases,  removing  the  cause  of  the  malady  from  the  blood,  and 


ELIMINATING  ACTION  OF  THE  SKIN.  429 

allowing  the  restorative  powers  free  play.  Again,  certain  forms  of 
Rheuraatism  are  characterized  by  copious  acid  perspirations  ;  and 
instead  of  endeavouring  to  check  these,  we  should  rather  encourage 
them  as  the  best  means  of  freeing  the  blood  from  its  undue  accumu- 
lation of  lactic  acid.  And  it  is  recorded  that  in  the  "  sweating  sick- 
ness," which  spread  throughout  Europe  in  the  16th  century,  no  re- 
medies seemed  of  any  avail  but  diaphoretics  ;  which,  aiding  the  powers 
of  nature,  concurred  with  them  to  purify  the  blood  of  its  morbific 
matter.  The  hot-air  bath,  in  some  cases,  and  the  wet  sheet  (which, 
as  used  by  the  Hydropathists,  is  one  of  the  most  powerful  of  all  dia- 
phoretics), will  be  probably  employed  more  extensively  as  therapeutic 
agents,  in  proportion  as  the  importance  of  acting  on  the  skin,  as  an 
extensive  collection  of  glandulse,  comes  to  be  better  understood. 
The  absurdity  of  the  "Hydropathic"  treatment  consists  in  its  indis- 
criminate application  to  a  great  variety  of  diseases ;  no  person,  who 
has  watched  its  operation,  can  deny  that  it  is  a  remedy  of  a  most 
powerful  kind  ;  and  if  its  agency  be  fairly  tested,  there  is  strong  rea- 
son to  believe,  that  it  will  be  found  to  be  the  most  valuable  curative 
means  we  possess  for  various  specific  diseases,  which  depend  upon 
the  presence  of  a  definite  "  materies  morbi"  in  the  blood,  especially 
Gout  and  chronic  Rheumatism ;  as  well  as  for  that  depressed  state  of 
the  general  system,  which  results  from  the  "wear  and  tear"  of  the 
bodily  and  mental  powers. 

749.  The  Mucous  surface  of  the  Alimentary  Canal  is  furnished, 
like  the  skin,  with  a  vast  number  of  glandulee,  varying  in  complexity, 
from  the  simple  follicle,  to  a  mass  consisting  of  numerous  lobules 
opening  into  a  common  excretory  duct.  The  functions  of  these,  as 
already  pointed  out,  are  equally  various.  The  simple  follicles  ap- 
pear destined,  for  the  most  part,  to  secrete  the  protective  mucus,  which 
intervenes  between  the  membranous  wall  and  the  substances  contained 
in  the  canal,  and  which  serves  to  protect  the  former  from  the  irritat- 
ing action  of  the  latter.  The  more  complex  follicles  of  the  Stomach 
elaborate  the  Gastric  fluid,  which  is  the  prime  agent  in  the  digestive 
process  (§  496).  But  there  is  strong  reason  to  believe,  that  the  func- 
tion of  the  numerous  glandulse,  which  beset  the  walls  of  the  small 
intestine,  and  which  are  known  as  Brunner's  and  Peyer's  glands 
(after  the  names  of  their  discoverers),  is  purely  excretory  ;  and  that 
they  are  destined  to  eliminate  putrescent  matters  from  the  blood,  and 
to  convey  them,  by  the  readiest  channel,  completely  out  of  the  body. 
That  the  putrescent  elements  of  the  feces  are  not  immediately  de- 
rived from  the  food  taken  in,  so  much  as  from  the  secreting  action 
of  the  intestinal  glandulse,  appears  from  this  consideration  ; — that 
fecal  matter  is  still  discharged,  even  in  considerable  quantities,  long 
after  the  intestinal  tube  has  been  completely  emptied  of  its  alimentary 
contents.  We  see  this  in  the  course  of  many  diseases,  when  food  is 
not  taken  for  many  days,  during  which  time  the  bowels  are  com- 
pletely emptied  of  their  previous  contents  by  repeated  evacuations ; 
and  whatever  then  passes,  must  be  derived  from  the  intestinal  walls 


430  GENERAL  RELATIONS  OF  EXCRETING  PROCESSES. 

themselves.  Sometimes  a  copious  flux  of  putrescent  matter  con- 
tinues to  take  place  spontaneously  ;  whilst  it  is  often  produced  by  the 
agency  of  purgative  medicine.  The  "  colliquative  diarrhoea,"  which 
frequently  comes  on  at  the  close  of  exhausting  diseases,  and  which 
usually  precedes  death  by  starvation,  appears  to  depend,  not  so  much 
upon  a  disordered  state  of  the  intestinal  glandul8e,  as  upon  the  gene- 
ral disintegration  of  the  solids  of  the  body,  which  calls  them  into  ex- 
traordinary activity,  for  the  purpose  of  separating  the  decomposing 
matter. 

750.  Thus  we  perceive,  that  we  have  here,  also,  to  watch  for  the 
indications  of  Nature ;  and  that  this  extensive  system  of  intestinal 
glandulse,  being  the  principal  channel  for  the  elimination  of  putres- 
cent matters  from  the  blood,  should  be  especially  attended  to,  when 
there  is  reason  to  think  that  such  matters  are  present  in  too  large  an 
amount.  Hence,  when  diarrhoea  is  already  existing,  we  may  often 
do  more  good  by  allowing  it  to  take  its  course,  or  even  by  increasing 
it  by  the  agency  of  purgative  medicines,  than  by  attempting  to  check 
it,  and  thus  causing  the  retention  of  the  morbid  matter  in  the  circu- 
lating current.  But,  on  the  other  hand,  it  is  necessary  to  bear  in  mind 
the  extreme  irritability  of  the  intestinal  raucous  membrane ;  and  care- 
fully to  avoid  exciting  it,  when  it  is  already  in  excess,  or  when  there 
is  danger  that  it  will  supervene, — as  in  that  form  of  Fever  in  which 
there  is  a  peculiar  liability  to  inflammation  and  ulceration  of  the  walls 
of  the  alimentary  canal. 

5.   General  Summary  of  the  Excreting  Processes. 

751.  We  have  now  passed  in  review  the  various  processes,  by 
which  the  products  of  the  disintegration  of  the  animal  tissues  are  car- 
ried off*;  and  we  have  seen  that  the  necessity  for  their  removal  is 
much  more  urgent  than  for  their  replacement.  A  cold-blooded  animal 
may  subsist  for  some  weeks,  or  even  months,  without  a  fresh  supply 
of  food  ;  the  waste  of  its  tissues  being  so  small,  if  it  remain  in  a  state 
of  rest,  as  to  be  quite  compatible  with  the  continuance  of  its  life  ;  and 
a  warm-blooded  animal  may  live  for  many  days  or  even  weeks,  pro- 
vided that  it  has  in  its  body  a  store  of  fat  sufficient  to  keep  up  its 
heat  by  the  combustive  process.  But  in  either  case,  if  the  exhalation 
of  carbonic  acid  by  the  lungs,  the  elimination  of  biliary  matter  by  the 
liver,  the  separation  of  urea  or  uric  acid  by  the  kidneys,  or  the  with- 
drawal of  putrescent  matter  by  the  intestinal  glandule,  be  completely 
checked,  a  fatal  result  speedily  ensues; — more  speedily  in  warm- 
blooded animals  than  in  those  which  cannot  sustain  a  high  inde- 
pendent temperature,  on  account  of  the  greater  proneness  to  decom- 
position in  the  bodies  of  the  former,  than  in  those  of  the  latter; — and 
more  speedily  in  the  latter,  when  their  bodies  are  kept  at  an  elevated 
temperature  by  the  warmth  of  the  surrounding  medium,  than  when 
the  degree  of  heat  is  so  low,  that  there  is  little  proneness  to  sponta- 
neous change  in  the  substance  of  their  bodies. 


RELATIONS  OF  BILIARY  AND  PULMONARY  EXCRETIONS.       431 

752.  It  may  be  taken  as  a  general  principle,  in  regard  to  the 
Excreting  processes  (including  Respiration),  that  they  have  a  three- 
fold purpose  ; — in  the  first  place,  to  carry  off  the  normal  results  of  the 
waste  or  disintegration  of  the  solid  tissues,  and  of  the  decomposition 
of  the  fluids;  in  the  second  place,  to  draw  off  the  superfluous  aliment- 
ary matter,  which,  though  received  into  the  circulating  current,  is 
not  converted  into  solid  tissue,  in  consequence  of  the  want  of  demand 
for  it ; — and  in  the  third  place,  to  carry  off  the  abnormal  products, 
which  occasionally  result  from  irregular  or  morbid  changes  in  the 
system.  Thus  by  the  Lungs  are  excreted  a  large  amount  of  carbon, 
and  some  hydrogen,  resulting  from  the  disintegration  of  the  tissues, 
especially  the  nervous  and  muscular;  the  same  elements  in  animals 
that  take  in  a  large  proportion  of  farinaceous  or  oleaginous  aliment, 
may  be  derived  immediately  from  the  food,  without  any  previous 
conversion  into  solid  tissue ;  and  there  can  be  little  doubt  that  the 
respiratory  function  is  also  an  important  means  of  purifying  the  blood 
from  various  deleterious  matters,  either  introduced  from  without  (such 
as  narcotic  poisons),  or  generated  within  the  body  (such  as  the  poison 
of  fever*).  And  it  is  important  to  bear  this  last  circumstance  in  mind  ; 
since  it  enables  us  to   understand  how,  if  time  be  given,  the  system 

frees  itself  from  such  noxious  substances  ;  and  points  out  the  duty  of 
the  medical  attendant  to  be  rather  that  of  supporting  the  powers  of 
the  body  by  judiciously  devised  means,  and  of  aiding  the  elimination 
of  the  morbid  matter  through  the  lungs  and  skin  by  a  copious  supply 
of  pure  air,  than  of  interfering  more  actively  to  promote  that  which 
Nature  is  already  effecting  in  the  most  advantageous  manner. 

753.  In  like  manner,  the  Liver  is  charged  with  the  separation  of 
hydrocarbon,  in  a  fluid  form ;  for  which  a  supply  of  oxygen  is  not 
requisite.  This  product  is  partly  derived  from  the  waste  of  the  sys- 
tem; but  the  arrangement  of  the  biliary  vessels  leads  to  the  belief, 
that  much  of  it  is  at  once  derived  from  crude  matter,  taken  up  by  the 
mesenteric  veins,  and  eliminated  from  them  by  the  hepatic  cells, 
without  ever  passing  into  the  general  circulation.  And  various  facts 
seem  to  indicate,  that  the  Liver  is  also  destined  to  remove  from  the 
blood  extraneous  substances,  which  are  noxious  to  it.  Thus,  in  cases 
where  death  has  resulted  from  the  prolonged  introduction  of  the  salts 
of  Copper  into  the  system,  a  considerable  amount  of  that  metal  has 
been  obtained  from  the  substance  of  the  gland. — It  has  been  already 
pointed  out  (§  720)  that  the  Liver  and  Respiratory  organs  are  deve- 
loped in  an  inverse  proportion  to  each  other,  in  the  different  classes 
of  animals ;  the  Liver  being  largest  where  the  respiration  is  most 
feeble,  and  vice  versa.  Now  it  is  important  to  bear  in  mind,  that  the 
functional  activity  of  the  liver  in  any  individual  must  be  in  like 
manner  the  greater,  as  the  amount  of  respiration  is  less ;  the  hydro- 

*  There  is  strong  reason  to  believe  that,  in  many  instances,  a  small  amount  of 
poisonous  matter  introduced  from  without,  in  the  form  of  a  contagion  or  miasm,  may 
lead,  by  a  process  resembling  fermentation,  to  the  production  of  a  large  quantity  of 
similar  noxious  substances  in  the  animal  fluids. 


432  DEPURATING  ACTION  OF  THE  KIDNEYS. 

carbon,  which  is  eliminated  by  the  lungs,  when  their  activity  is  the 
greatest,  being  thrown  upon  the  liver  for  separation,  when  the  respi- 
ration is  feeble.  We  have  seen  that  the  amount  of  carbonic  acid 
exhaled  at  high  temperatures,  is  much  less  than  that  set  free  in  a 
colder  atmosphere ;  consequently,  the  liver  is  called  upon  to  do  more 
in  warm  climates,  and  is  therefore  peculiarly  liable  to  disordered 
action, — unless  the  diet  be  carefully  regulated,  in  accordance  with  the 
wants  of  the  system. 

754.  The  effects  of  diminished  respiration,  in  producing  an  increase 
in  the  fatty  constituents  of  the  liver,  are  peculiarly  well  marked  in  the 

diseased  condition  produced  in  the  geese,  that  are 
Fig.  127.  being  prepared  for  celebrated  Strasburg  pates.     The 

unfortunate  bird  is  closely  confined  at  a  high  tem- 
perature ;  so  that  the  respiration  is  reduced  to  its 
minimum  amount  by  the  combined  effects  of  warmth 
_  and  muscular  inaction ;  and  it  is  then  crammed  with 
ged^^with  Faf:-°a,  maizc,  which  contains  a  large  amount  of  oily  matter. 
So'^sl' globules.''  ^'  The  consequence  is,  that  its  liver  soon  enlarges,  and 
becomes  unusually  fatty ;  its  cells  being  gorged  with 
oil-globules,  instead  of  each  containing  no  more  than  one  or  two  :  and 
it  is  then  ready  for  the  epicureans  who  set  so  high  a  value  on  the 
pate  defoie  gras.  A  similar  diseased  condition  of  the  liver  frequently 
presents  itself  in  Man,  as  a  consequence  of  chronic  disorders  of  the 
respiratory  organs,  which  diminish  the  amount  of  hydrocarbon  elimi- 
nated through  their  agency ;  this  "  fatty  liver"  is  peculiarly  common 
in  the  advanced  stages  of  Phthisis. 

755.  With  regard  to  the  Kidneys,  it  has  been  already  pointed  out 
that  they  are  the  special  emunctories  of  the  azotized  products  of  the 
decomposition  of  the  tissues ;  and  that  they  serve  also  to  convey  away 
the  overplus  of  such  earthy  and  alkaline  salts,  as  are  readily  soluble. 
Moreover,  it  has  been  shown  that  the  surplus  proteine-compounds, 
which  are  not  required  for  the  nutrition  of  the  system,  must  be  ex- 
creted by  their  agency,  after  having  been  metamorphosed  into  urea. 
And  we  have  now  to  notice,  that  other  matters  of  an  injurious  charac- 
ter, whether  introduced  from  without,  or  generated  within  the  sys- 
tem, are  drawn  off  by  the  same  channel.  Thus  the  saline  compounds, 
taken  up  by  the  absorbent  process  (§  493),  are  for  the  most  part  set 
free  through  these  organs ;  especially  when  their  properties  are  such, 
as  to  excite  the  action  of  the  kidneys  in  a  peculiar  degree.  Thus, 
Prussiate  of  Potash  has  been  detected  in  the  urine,  within  two  mi- 
nutes after  it  had  been  introduced  into  the  stomach.  It  has  been 
sometimes  noticed  that  Iodide  of  Potassium,  when  administered  as 
a  medicine,  is  retained  w^ithin  the  body  for  some  days,  producing  ex- 
tensive cutaneous  eruptions,  or  some  other  unusual  consequence;  and 
that  it  then  suddenly  begins  to  pass  off  by  the  kidneys,  and  is  ex- 
creted in  very  large  quantities.  The  effect  of  the  inhalation  of  the 
vapour  of  turpentine,  even  in  a  very  diluted  state,  in  speedily 
imparting  to  the  urine  the  odour  of  violets,  is  an  evidence  that  not 


DEPURATING  ACTION  OF  SKIN,  ETC.  433 

merely  the  actual  substances  imbibed,  but  new  and  peculiar  com- 
pounds to  which  they  give  rise,  are  thus  eliminated  by  the  Kidneys. 

756.  The  most  singular  variations  in  the  excretory  function  of  the 
Kidneys  are  seen,  however,  when  the  Urine  is  charged  with  sub- 
stances which  are  not  only  foreign  to  it,  but  are  altogether  foreign 
to  the  healthy  body.  The  most  remarkable  instance  of  this  is  seen 
in  the  disease  termed  Diabetes,  in  which  a  large  quantity  of  Sugar  is 
formed,  either  directly  from  the  food,  or  by  the  disintegration  of  the 
solid  tissues ;  and  in  which  this  compound  is  eliminated  by  the  Kid- 
neys, imparting  to  the  urine  a  saccharine  taste.  And  another  example 
of  the  same  general  fact  is  seen  in  the  "oxalic  diathesis,"  in  which 
an  unusual  arrangement  of  the  elements,  that  usually  form  urea  or 
uric  acid,  gives  rise  to  a  new  and  peculiar  compound,  oxalate  of  am- 
monia; this  being  drawn  off'  by  the  kidneys,  and  being  decomposed 
by  the  calcareous  matter  present  in  the  urine,  gives  rise  to  a  deposit 
of  oxalate  of  lime.  In  the  treatment  of  such  diseases,  our  attention 
must  be  given,  not  so  much  to  the  secreting  organ,  as  to  the  condition 
of  the  system  at  large,  of  which  the  character  of  the  secreted  product 
is  the  indication  or  exponent. 

757.  To  what  has  already  been  stated  in  regard  to  the  exhalant 
functions  of  the  Lungs  and  Skin,  it  may  be  added  that  many  states 
of  disease  are  marked  by  an  unusual  odour  emitted  from  the  body; 
and  there  can  be  little  doubt  that  the  peculiar  odorous  matter  is  pre- 
formed in  the  blood, — as  we  know  that  the  ordinary  scent  of  any 
species  (whether  Man,  Dog,  Horse,  Goat,  &c.,)  may  be  set  free  from 
the  blood  of  that  species,  by  the  addition  of  sulphuric  acid.  The  ex- 
istence of  such  odours,  therefore,  is  not  to  be  attributed  to  disordered 
function  in  the  excreting  organs ;  but  to  the  formation  of  morbid  pro- 
ducts in  the  interior  of  the  body,  which  these  organs  do  their  best  to 
remove.  The  fetid  breath,  which  frequently  accompanies  an  attack 
of  indigestion,  is  another  instance  of  the  power  of  the  lungs  to  eli- 
minate not  merely  Carbonic  acid,  but  other  products  of  the  changes 
in  composition,  which  the  food  undergoes  when  introduced  into  the 
system. 

758.  The  same  remarks  apply,  and  with  yet  greater  force,  to  the 
intestinal  glandulse  ;  whose  function  it  is,  not  merely  to  remove  the 
putrescent  matter  ordinarily  formed  by  the  disintegration  of  the  tis- 
sues, or  by  the  decomposition  of  unassimilated  food,  but  also  to  draw 
off*  the  still  more  offensive  products  of  such  changes  as  take  place  in 
disease.  Thus  there  are  conditions  of  the  system,  in  which,  without 
any  well-marked  disorder,  the  feces  emit  a  peculiarly  fetid  odour ; 
and  with  these  is  almost  always  associated  a  depressed  state  of  mind. 
Now  it  can  scarcely  be  doubted,  that  the  real  fault  is  here  rather  in 
the  early  part  of  the  nutritive  operations,  than  in  the  excretory  func- 
tion; and  that  the  fetor  of  the  contents  of  the  intestine  depends  upon 
the  undue  formation  of  putrescent  naatter  in  the  system,  which,  by 
tainting  the  blood,  causes  its  action  upon  the  brain  to  become  un- 
healthy.    The  object  of  the  physician  will  be  here  to  eliminate  the 

28 


434  HEAT  OF  ANIMALS  AND  PLANTS. 

morbid  product,  by  the  moderate  use  of  purgatives ;  and  so  to  regu- 
late the  diet  and  regimen,  as  to  correct  the  tendency  to  its  formation. 
— An  excessive  fetor  in  the  evacuations,  as  well  as  in  the  exhalations 
from  the  skin  and  lungs,  is  peculiarly  characteristic  of  those  very  se- 
vere forms  of  typhus  (now,  happily,  of  comparatively  rare  occurrence), 
which  are  termed  putrid  fevers.  Here  the  whole  of  the  solids  and 
fluids  of  the  body  appear  to  have  an  unusual  tendency  to  decomposi- 
tion, in  consequence  of  the  introduction  of  some  morbid  agent,  which 
acts  as  a  ferment;  and  the  system  attempts  to  free  itself  from  the  pro- 
ducts of  that  decomposition,  by  the  various  organs  of  excretion,  par- 
ticularly the  Skin  and  intestinal  surface. 

759.  It  is  of  great  importance  that  the  Student  should  form  clear 
conceptions  on  this  subject;  and  that  he  should  not  (as  too  often 
happens),  by  directing  his  remedies  to  the  mere  symptoms  or  results 
of  a  disease,  act  in  precise  opposition  to  the  natural  tendency  of  the 
system  to  free  itself  from  some  unusual  noxious  matter,  through  those 
channels  which  are  ordinarily  destined  to  carry  off  only  the  regular 
products  of  its  disintegration. 


CHAPTER  X. 

OF  THE  DEVELOPMENT  OF  HEAT,  LIGHT,  AND  ELECTRICITY  IN  THE 
ANIMAL  BODY. 

760.  It  has  been  shown,  in  an  earlier  part  of  this  volume  (Chap. 
II.),  that  all  Vital  actions  require  a  certain  amount  of  Heat  for  their 
performance  ;  and  that  there  is  a  great  variety  amongst  the  different 
classes  of  Animals,  both  in  regard  to  the  degree  of  Heat  which  is 
most  favourable  to  the  several  processes  of  their  economy,  and  in 
regard  to  their  own  power  of  sustaining  it,  independently  of  oscilla- 
tions in  the  temperature  of  the  surrounding  medium.  As  a  general 
rule,  the  Invertebrated  animals  are  cold-blooded ;  that  is,  they  have 
little  or  no  power  of  sustaining  an  independent  temperature.  The 
degree  of  energy  of  their  vital  actions  entirely  depends,  therefore, 
upon  the  Avarmth  they  receive  from  the  air  or  water  they  inhabit;  they 
have  no  power  of  resisting  the  depressing  influence  of  cold  ;  and  they 
are  generally  so  organized,  as  to  pass  into  a  state  of  complete  inaction 
or  torpidity,  when  the  temperature  sinks  below  a  certain  point, — after 
gradually  becoming  more  and  more  inert  with  every  diminution  in  the 
heat  of  their  bodies.  The  same  is  true,  also,  of  most  Fishes  and 
Reptiles :  but  the  animals  of  the  former  class,  from  the  more  equable 
temperature  of  the  medium  they  inhabit,  are  not  so  liable  to  be  re- 
duced to  inaction  as  the  latter  ;  being  usually  so  organized,  as  to  retain 
their  activity  so  long  as  the  water  around  them  continues  liquid  ;  and 


HEAT  OF  ANIMALS  AND  PLANTS.  435 

being  actually  imbedded  in  a  frozen  state,  when  the  water  around 
them  is  converted  into  ice,  without  the  loss  of  their  vitality.  There 
are  certain  Fishes,  however,-r-such  as  the  Tunny,  Sword-fish,  and 
other  large  species  of  the  Mackarel  tribe, — which  are  able  to  sustain 
a  temperature  considerably  above  that  of  the  sea  they  inhabit ;  thus 
in  the  Bonito,  the  heat  of  the  body  has  been  found  to  be  99°,  when 
the  temperature  of  the  surrounding  sea  was  but  80^°.  It  is  not  pro- 
bable, however,  that  the  temperature  of  the  body  would  be  kept  up 
to  the  same  standard,  if  that  of  the  sea  should  be  considerably  low- 
ered ;  but  it  would  probably  remain  at  from  18°  to  20°  above  the  latter. 
And  in  like  manner,  it  has  been  noticed  that  many  of  the  more  active 
Reptiles  possess  the  power  of  sustaining  the  temperature  of  their 
bodies  at  10°  or  15°  above  that  of  the  surrounding  air. 

761.  The  classes  of  animals,  which  are  especially  endowed  with 
the  power  of  producing  and  maintaining  heat,  are  Insects,  Birds,  and 
Mammalia.  The  remarkable  variations  which  present  themselves  in 
the  temperature  of  the  first  of  these  classes,  and  the  connection  of 
these  variations  with  the  condition  of  the  animals,  in  regard  to  ac- 
tivity or  repose,  have  already  been  sufficiently  noticed  (§  123). — The 
temperature  of  Birds  is  higher  than  that  of  any  other  class  of  ani- 
mals; varying  from  100°  to  111°  or  112°.  The  lowest  degree  is 
found  in  some  of  the  aquatic  species,  as  the  Gull,  and  in  those  which 
principally  live  on  the  ground,  as  the  Fowl  tribe  ;  and  the  highest  in 
the  birds  of  most  active  flight,  as  the  Swallow.  The  temperature  of 
the  Mammalia  seems  to  range  from  about  96°  to  104°;  that  of  Man 
has  been  observed  as  low  as  96J°,  and  as  high  as  102°.  The  varia- 
tions are  dependent  in  part  upon  the  temperature  of  the  external  air; 
but  are  influenced  also  by  the  general  condition  of  the  body,  as  to 
repose  or  activity,  the  period  of  the  day,  the  time  that  has  elapsed 
since  a  meal,  &c.  A  somewhat  larger  amount  of  caloric  is  generated 
during  the  day,  than  in  the  night ;  and  the  body  is  usually  warmer, 
by  a  degree  or  two,  at  noon,  than  at  midnight.  There  is  also  a  slight 
increase  during  the  digestion  of  a  meal;  and  exercise  is  a  powerful 
means  of  raising  the  temperature. — The  range  of  temperature  is  much 
greater  in  disease  ;  thus  the  thermometer  has  been  seen  to  rise  to  106° 
in  Scarlatina  and  Typhus,  and  to  110f°  in  Tetanus;  whilst  it  has 
fallen  to  82°  in  Spasmodic  Asthma,  and  to  77°  in  Cyanosis  and  Asiatic 
Cholera. 

762.  In  searching  for  the  conditions,  on  which  this  production  of 
heat  within  the  Animal  body  is  dependent,  it  is  very  important  to 
bear  in  mind,  that  a  similar  generation  of  Caloric  may  be  observed 
in  the  Vegetable  kingdom.  It  appears  from  the  most  recent  and 
exact  experiments,  that  all  living  Plants  are  somewhat  warmer  than 
similar  dead  plants  exposed  to  the  same  atmosphere  ;  and  that  the 
elevation  is  the  greatest  in  the  leaves  and  young  stems,  in  which  the 
most  active  vital  changes  are  taking  place.  But  the  most  decided 
production  of  heat  occurs  in  \he  flowering  of  certain  Plants,  such  as 
the  Arum,  which  have  large  fleshy  receptacles,  on  which  a  great 


436  CONDITIONS  OF  DEVELOPMENT  OF  HEAT. 

number  of  blossoms  are  crowded  ;  thus  a  thermometer  placed  in  the 
centre  of  five  spadixes  of  the  Arum  cordifolium  has  been  seen  to 
rise  to  lll°;  and  one  placed  in  the  midst  of  twelve  spadixes  has  risen 
to  121°;  whilst  the  temperature  of  the  surrounding  air  was  only  Q>Q°, 
In  the  germination  of  seeds,  also,  a  great  elevation  of  temperature 
occurs;  which  is  rendered  most  evident  by  bringing  together  a  num- 
ber of  seeds,  as  in  the  process  of  malting^  so  that  the  caloric  is  not 
dissipated  as  fast  as  it  is  generated  ;  the  thermometer,  placed  in  the 
midst  of  a  mass  of  seeds  in  active  germination,  has  been  seen  to  rise 
to  110°. 

763.  Thus  it  is  evident  that  the  chemical  changes,  which  are  in- 
volved in  the  operations  of  Nutrition,  are  capable  of  setting  free  a 
large  amount  of  heat ;  which,  although  ordinarily  dissipated  from 
tiie  vegetating  surface  too  speedily  to  manifest  itself,  becomes  sensible 
enough,  when  this  rapid  loss  is  checked.  If  we  further  examine  into 
the  nature  of  the  chemical  changes,  which  appear  most  concerned  in 
this  elevation  of  temperature,  we  find  that  they  uniformly  consist  in 
the  combination  of  the  carbon  of  the  plant  with  the  oxygen  of  the 
atmosphere;  so  that  a  large  quantity  of  carbonic  acid  is  formed  and 
set  free,  precisely  in  the  manner  of  the  Respiration  of  Animals.  This 
process  is  so  slowly  performed,  in  the  ordinary  growth  of  Plants,  that 
it  is  concealed  (as  it  were)  by  the  converse  change, — Xh^  fixation  of 
carbon  from  the  carbonic  acid  of  the  atmosphere,  under  the  influence 
of  light  (§  83).  But  it  takes  place  with  extraordinary  energy  during 
flowering  and  germination;  a  large  quantity  of  carbon  being  set  free, 
'by  union  with  the  oxygen  of  the  air ;  and  the  starchy  matter  of  the 
Teceptacle,  or  of  the  seed,  being  converted  into  sugar.  Now  it  has 
been  ascertained  by  careful  experiments,  that  the  amount  of  heat  gene- 
rated is  in  close  relation  with  the  amount  of  carbonic  acid  set  free; 
and  that,  if  the  formation  of  the  latter  be  prevented,  by  placing  the 
flower  or  the  seed  in  nitrogen  or  hydrogen,  no  elevation  of  tempera- 
ture takes  place  ;  whilst  if  the  process  be  stimulated  by  pure  oxygen, 
so  that  a  larger  proportion  of  carbonic  acid  is  evolved,  the  elevation 
of  temperature  is  more  rapid  and  considerable  than  usual. 

764.  Upon  examining  into  the  conditions  under  which  Caloric  is 
generated  in  the  Animal  body,  we  find  them  essentially  the  same. 
Wherever  the  temperature  of  the  body  is  maintained  at  a  regular 
standard,  so  as  to  be  independent  of  variations  in  the  warmth  of  the 
surrounding  medium,  we  find  a  provision  for  exposing  the  blood  most 
freely  to  the  influence  of  oxygen,  and  for  extricating  its  carbonic  acid ; 
thus  in  Birds  and  Mammals,  the  blood  is  distributed,  in  a  minute  ca- 
pillary network,  on  the  walls  of  the  pulmonary  air-cells,  the  gaseous 
contents  of  which  are  continually  renewed  ;  and  in  Insects,  the  air  is 
carried  into  every  part  of  the  body,  by  the  ramifying  trachese.  We 
constantly  find  a  proportion  between  the  amount  of  heat  evolved,  and 
that  of  carbonic  acid  generated  ;  this  is  peculiarly  evident  in  Insects, 
whose  respiration  and  calorification  vary  so  remarkably  (§  123);  but 
it  is  also  proved  by  comparing  the  amount  of  carbonic  acid  generated 


CONDITIONS  OF  DEVELOPMENT  OF  HEAT,  437 

by  warm-blooded  animals,  when  the  external  temperature  is  low,  and 
when  more  heat  must  be  evolved  to  keep  the  temperature  of  their 
bodies  up  to  its  proper  standard,  with  that  generated  by  the  same 
animals  in  a  warmer  atmosphere,  when  the  proper  animal  heat  is 
diminished  in  amount  (§  691). 

765.  The  sources  of  the  Carbonic  Acid  thrown  off  by  the  lungs, 
have  been  already  pointed  out  (Chap.  VIII.):  it  is  partly  derived 
from  the  metamorphosis  of  the  tissues;  but  partly,  in  all  but  purely 
carnivorous  animals,  more  directly  from  the  non-azotized  portion  of 
the  food.  The  precise  mode  in  which  the  carbon  of  this  is  united 
with  the  oxygen  derived  from  the  atmosphere,  is  not  yet  known  ;  but 
it  is  certain  that,  in  whatever  manner  the  combination  takes  place,  a 
certain  measure  of  caloric  must  be  generated.  It  appears,  however, 
from  various  experiments,  that  the  whole  quantity  of  caloric  gene- 
rated by  an  animal  in  a  given  time,  is  greater  than  that  which  would 
be  evolved  by  the  combustion  of  the  carbon,  included  in  the  carbonic 
acid  evolved  during  the  same  time.  Hence  it  is  evident  that  other 
chemical  processes  occurring  within  the  body  are  concerned  in  the 
maintenance  of  the  temperature  ;  and  it  is  not  difficult  to  point  to 
some  of  these.  It  is  probable,  in  the  first  place,  that  some  of  the 
hydrogen  of  the  food  may  be  "  burned  off"  by  union  with  the  oxygen 
of  the  atmosphere,  so  as  to  form  part  of  the  water  which  is  exhaled 
from  the  lungs.  Again,  the  sulphur  and  phosphorus  of  the  food 
are  converted,  by  oxygenation,  into  sulphuric  and  phosphoric  acids; 
in  which  process,  heat  must  be  generated.  In  the  composition  of 
urea,  moreover,  oxygen  is  present  in  much  larger  proportion,  than  it 
is  in  the  proteine-compounds  by  the  metamorphosis  of  which  it  is 
formed  ;  so  that  in  its  production,  too,  caloric  will  be  generated.  In 
fact  it  may  be  stated  as  a  general  truth,  that  the  whole  excess  of  the 
oxygen  absorbed  over  that  which  is  contained  in  the  carbonic  acid 
exhaled  (§  690),  must  be  applied  to  purposes  in  the  laboratory  of 
the  system,  in  which  caloric  will  be  disengaged.  Still,  the  amount 
of  carbonic  acid  exhaled  must  always  be  the  measure  of  the  chemical 
processes,  by  which  heat  is  generated  in  the  body ;  because  it  is 
itself  the  result  of  the  chief  of  these  processes  (the  union  of  carbon 
and  oxygen),  and  because  the  surplus  amount  of  oxygen  which  is 
absorbed,  and  w^hich  is  applied  to  other  purposes,  entirely  depends 
upon  it. 

766.  The  power  of  maintaining  a  high  independent  temperature  is 
usually  much  less  in  young  warm-blooded  animals,  than  in  adults. 
There  are  considerable  variations  in  this  respect,  however,  amongst 
different  species ;  for  where  the  young  animal  is  born  in  such  an  ad- 
vanced condition,  as  to  be  thenceforth  almost  independent  of  parental 
assistance,  it  is  capable  of  maintaining  its  own  temperature  ;  but 
where  it  is  born  in  such  a  state  as  to  require  to  be  supplied  wdth 
food  by  the  parent  for  some  time,  it  is  also  more  or  less  dependent 
upon  the  warmth  imparted  to  it  from  the  parental  body.  This  is 
peculiarly  the  case  with  the  young  of  the  Human  species,  which  is 


438  REGULATION  OF  HEAT  IN  MAN. 

longer  dependent  upon  parental  aid,  than  that  of  any  other  animal. 
In  the  case  of  children  born  very  prematurely,  the  careful  sustenance 
of  their  heat  is  one  of  the  points  most  to  be  attended  to  in  rearing 
them  ;  and  even  the  most  vigorous  infants,  born  at  the  full  time,  are 
far  from  being  able  to  keep  up  their  proper  standard  without  assist- 
ance, if  exposed  to  a  cool  atmosphere.  It  has  been  ascertained  that, 
during  the  first  month  of  infant  life,  the  mortality  in  winter  is  nearly 
double  that  of  summer, — being  1*39  in  January  to  0-78  in  July  ;  and 
this  striking  difference  cannot  be  attributed  to  any  other  cause,  than 
the  injurious  influence  of  external  cold,  which  the  calorifying  powers 
of  the  infant  do  not  enable  it  to  resist.  As  age  advances,  the  power 
of  generating  heat  increases,  and  the  body  becomes  much  more  inde- 
pendent of  external  vicissitudes  ;  so  that,  in  adult  life,  the  winter 
mortality  is  to  that  of  summer,  only  as  1*05  to  0-91,  or  less  than  one- 
sixth  more.  In  advanced  age,  the  calorifying  power  again  diminishes ; 
and  this  we  should  anticipate,  from  the  general  torpor  of  the  nutritive 
operations  in  old  persons.  Between  50  and  65  years  of  age,  the  re- 
lative winter  and  summer  mortality  are  nearly  as  in  the  first  month  of 
infancy ;  and  at  90  years,  the  average  mortality  of  winter  is  much 
more  than  twice  that  of  summer,  being  as  1*58  to  64. 

767.  It  appears  that  there  is  not  merely  a  difference  in  calorifying 
power  at  different  ages,  but  at  different  seasons ;  the  amount  of  heat 
generated  in  summer  not  being  sufficient,  in  many  animals,  to  prevent 
the  body  from  being  cooled  down  by  prolonged  exposure  to  a  tempe- 
rature, which  is  natural  to  them  in  winter.  To  what  extent  this  is 
the  case  with  Man,  it  is  difficult  to  say.  His  constitution  is  distin- 
guished by  its  power  of  adapting  itself  to  circumstances  ;  and  he  can 
live  under  extremes  of  temperature  more  wide  than  those,  which  most 
other  animals  can  endure  (§  113).  Whether  in  the  torrid  zone,  or 
in  the  arctic  regions,  he  can  maintain  his  healthy  condition  under 
favourable  circumstances;  in  each  case  his  natural  appetite  leading 
him  to  the  use  of  that  kind  and  amount  of  food,  which  are  best  suited 
to  the  wants  of  his  system.  But  the  longer  he  has  been  habituated 
to  a  very  warm  or  a  very  cold  climate,  the  more  difficult  he  at  first  finds 
it  to  live  comfortably  in  one  of  an  opposite  character ;  as  his  consti- 
tution, having  become  adapted  to  one  particular  set  of  circumstances, 
requires  time  to  accommodate  itself  to  an  opposite  one. 

768.  The  means  by  which  the  heat  of  the  body  is  prevented  from 
rising  above  its  normal  standard,  even  in  the  midst  of  a  very  high 
temperature  in  the  surrounding  air,  are  of  the  most  simple  character. 
The  excreting  action  of  the  skin  is  directly  stimulated  by  the  applica- 
tion of  warmth  to  the  surface;  and  the  fluid  which  is  poured  forth, 
being  immediately  vaporized,  converts  a  large  quantity  of  sensible 
caloric  into  latent,  and  thus  keeps  down  the  temperature  of  the  skin. 
By  this  provision,  the  body  may  be  exposed  with  impunity  to  dry  air 
of  600°  or  more,  so  long  as  the  supply  of  fluid  be  maintained.  But 
it  cannot  long  sustain  exposure  to  air  saturated  with  vapour,  even 


ANIMAL  LUMINOSITY.  439 

though  it  may  not  be  many  degrees  hotter  than  the  body ;  because 
the  cooling  act  of  evaporation  from  the  skin  cannot  then  be  carried  on. 

769.  The  evolution  of  Light  is  a  very  interesting  phenomenon, 
chiefly  witnessed  among  the  lower  Animals,  and  usually  supposed  not 
to  occur  in  any  class  above  Fishes.  It  is  particularly  remarkable 
among  the  Radiata  and  inferior  Mollusca.  A  large  proportion  of  the 
Acalephce,  or  Jelly-fish  tribe  possess  the  property  of  luminousness  in 
a  greater  or  less  degree ;  and  it  is  to  small  animals  of  this  class,  which 
sometimes  multiply  to  an  amazing  extent,  that  the  beautiful  phenome- 
non oi phosphorescence  of  the  sea  is  chiefly  due.  In  the  midst  of  the  soft 
diflfused  light  thus  occasioned,  brilliant  stars,  ribbons,  and  globes  of 
fire  are  frequently  seen ;  these  appearances  being  due  to  the  lumino- 
sity of  the  larger  species  of  the  same  tribe,  or  to  that  of  other  marine 
animals. — Some  of  the  most  remarkable  examples  of  luminosity,  in 
regard  to  the  brilliancy  of  the  light  emitted,  occur  in  the  class  of 
Insects.  Here  the  emission  is  confined  to  one  portion  of  the  body, 
or  to  two  or  more  isolated  spots,  instead  of  being  diffused  over  a  larger 
surface ;  and  it  is  proportionably  increased  in  intensity. 

770.  The  phenomenon  of  Animal  Luminousness  appears  usually 
attributable  to  the  formation  of  a  peculiar  secretion  ;  which,  in  many 
instances,  continues  to  shine  after  removal  from  the  Animal,  so  long 
as  it  is  exposed  to  the  influence  of  oxygen :  and  it  seems  not  unrea- 
sonable to  believe,  that  it  depends  upon  a  slow  process  of  combustion, 
analogous  to  that  which  takes  place  when  phosphorus  is  exposed  to 
the  air.  There  is  a  special  provision,  in  Insects,  for  conveying  a 
large  supply  of  air  through  the  peculiar  substance,  which  is  deposited 
beneath  the  luminous  spots ;  and  the  power  which  Glow-w^orms,  Fire- 
flies, &c.,  possess,  of  suddenly  extinguishing  their  light,  and  as  sud- 
denly renewing  it,  seems  to  depend  upon  their  control  over  the  air- 
aperture  or  spiracle  by  which  air  is  admitted, — the  stoppage  of  the 
supply  of  air  causing  the  immediate  cessation  of  the  luminousness, 
and  its  re-admission  occasioning  a  renewal  of  the  process  on  which  it 
depends. — It  is  probable,  however,  that  in  certain  cases,  the  lumino- 
sity is  rather  of  an  electrical  character.  There  are  several  of  the  smaller 
Annelida  or  marine  Worms,  which  are  brilliantly  luminous  when  irri- 
tated ;  the  luminosity  having  the  character,  however,  of  a  succession 
of  sparks,  rather  than  of  a  steady  glow.  It  appears  from  the  recent 
experiments  of  M.  Quatrefages,  that  this  peculiar  luminosity  is  the 
especial  attribute  of  the  muscular  system ;  and  that  it  is  produced  w4th 
every  act  of  muscular  contraction  in  these  animals. 

771.  Although  no  such  luminosity  is  commonly  manifested  in  any 
of  the  higher  vertebrata,  or  in  Man,  yet  there  are  well-authenticated 
cases,  in  which  the  phenomenon  has  presented  itself  in  the  living  sub- 
ject,*— luminous  emanations  from  dead  animal  matter  being  of  no 
unfrequent  occurrence.     In  most  of  these  cases,  however,  the  indi- 

*  See  an  account  of  several  cases  of  the  Evolution  of  Light  in  the  Living  Human 
Subject,  by  Sir  Henry  Marsh,  M.  D.,  M.  R.  L  A.,  &,c.^ 


440  ANIMAL  ELECTRICITY.— ELECTKIC  FISHES. 

viduals  exhibiting  the  luminosity  had  suffered  from  consumption,  or 
some  other  wasting  disease,  and  were  near  the  close  of  their  lives  at 
the  time ;  so  that  it  is  probable  that  a  decomposition  of  the  tissues  was 
actually  in  progress,  analogous  to  that  which,  when  it  occurs  after 
death,  imparts  luminosity  to  the  decaying  body.  One  instance  is 
recorded  in  which  a  large  cancerous  sore  of  the  breast  emitted  light 
enough,  to  enable  the  hands  on  a  watch-dial  to  be  distinctly  seen  when 
it  was  held  within  a  few  inches  of  the  ulcer ;  here,  too,  decomposition 
was  obviously  going  on,  and  the  phosphorescent  matter  produced  by 
it  was  exposed  to  the  oxygenating  action  of  the  atmosphere. 

771.  Slight  manifestations  of  free  Electricity ^  or,  in  other  words, 
disturbances  of  Electric  equilibrium,  are  very  frequent  in  living  ani- 
mals ;  and  they  are  readily  accounted  for,  when  we  bear  in  mind  that 
nearly  all  chemical  changes  are  attended  with  some  alteration  in  the 
electric  state  of  the  bodies  concerned ;  and  when  we  consider  the 
number  and  variety  of  such  changes  in  the  living  animal  body. 
When  slight,  however,  they  can  only  be  detected  by  refined  means 
of  observation;  and  it  is  only  when  they  are  considerable,  that  they 
attract  notice.  The  most  remarkable  examples  of  the  evolution  of 
free  Electricity  in  Animals,  are  to  be  found  in  certain  species  of  the 
class  of  Fishes ;  the  best  known  of  which  are  the  Torpedo  or  Elec- 
tric Ray,  and  the  Gymnotus  or  Electric  Eel.  These  possess  organs, 
in  which  Electricity  may  be  generated  and  accumulated  in  large  quan- 
tities, and  from  which  it  may  be  discharged  at  will.  The  shock  of  a 
large  and  vigorous  Gymnotus  is  sufficiently  powerful  to  kill  small 
animals,  and  to  paralyze  large  ones,  such  as  men  and  horses :  that  of 
the  Torpedo  is  less  severe,  but  it  is  sufficient  to  benumb  the  hand  that 
touches  it. 

772.  The  electric  organs  of  the  Torpedo  (which,  from  being  found 
on  European  shores,  has  been  the  most  studied)  are  of  flattened  shape, 
and  occupy  the  front  and  sides  of  the  body ;  forming  two  large  masses, 
which  extend  backwards  and  outwards  from  each  side  of  the  head. 
They  are  composed  of  two  layers  of  membrane  separated  by  a  con- 
siderable space ;  and  this  space  is  divided  by  vertical  partitions  into 
hexagonal  cells  like  those  of  a  honeycomb,  the  ends  of  which  are 
directed  towards  the  two  surfaces  of  the  body.  These  cells,  which 
are  filled  with  a  whitish  soft  pulp,  somewhat  resembling  the  substance 
of  the  brain,  but  containing  more  water,  are  again  subdivided  hori- 
zontally by  membranous  partitions;  and  all  these  partitions  are  pro- 
fusely supplied  with  blood-vessels  and  nerves. — The  electrical  organs 
of  the  Gymnotus  are  essentially  the  same  in  structure ;  but  they  differ 
in  shape,  in  accordance  with  the  conformation  of  the  animal. — In 
these,  and  the  other  Electrical  fishes,  the  electric  organs  are  supplied 
with  nerves  of  very  great  size,  larger  than  any  others  in  the  same 
animals,  and  larger  than  any  nerves  in  other  animals  of  similar  bulk. 
These  nerves  arise  from  the  top  of  the  spinal  cord,  and  seem  analo- 
gous to  the  pneumogastrics  of  other  animals. 

773.  The  following  conditions  appear  to  be  essential  to  the  mani- 


r 


ELECTRIC  FISHES.  441 

festation  of  the  Electric  powers  of  these  animals.  Two  parts  of  the 
body  must  be  touched  at  the  same  time ;  and  these  two  must  be  in 
different  electrical  states.  The  most  energetic  discharge  is  procured 
from  the  Torpedo,  by  touching  its  back  and  belly  simultaneously;  the 
electricity  of  the  back  being  positive,  and  that  of  the  belly  negative. 
When  two  parts  of  the  same  surface,  at  an  equal  distance  from  the 
electric  organ  are  touched,  no  effect  is  produced,  as  they  are  equally 
charged  with  the  same  electricity;  but  if  one  point  be  further  from  it 
than  the  other,  a  discharge  occurs,  the  intensity  of  which  is  propor- 
tioned to  the  difference  in  the  distance  of  the  points  from  the  electric 
organ.  However  much  a  Torpedo  is  irritated,  no  discharge  can  take 
place  through  a  single  point;  but  the  fish  makes  an  effort  to  bring  the 
border  of  the  other  surface  in  contact  with  the  offending  body,  through 
which  a  shock  is  then  transmitted.  This,  indeed,  is  probably  the  usual 
way  in  which  the  discharge  is  effected. — The  identity  of  animal  with 
common  Electricity  is  proved,  not  merely  by  the  similarity  of  the 
effects  upon  the  feelings  produced  by  the  shock  of  both  ;  but  also  by 
the  fact  that  a  spark  may  be  obtained,  and  chemical  decompositions 
effected  by  the  former,  precisely  as  by  the  latter. 

774.  The  voluntary  power  of  the  animal  over  its  Electric  organs,  is 
dependent  upon  their  connection  with  the  nervous  centres.  If  all  the 
nerve-trunks  supplying  the  organ  on  one  side,  be  divided,  the  animal's 
control  over  that  organ  will  be  destroyed  ;  but  the  power  of  the  other 
may  remain  uninjured.  If  the  nerves  be  partially  divided  on  either 
or  both  sides,  the  power  is  retained  by  the  portions  of  the  organs, 
which  are  still  connected  with  the  brain  by  the  trunks  that  remain. 
Even  slices  of  the  organ,  entirely  separated  from  the  body  except  by  a 
nervous  fibre,  may  exhibit  electrical  properties.  Discharges  may  be 
produced,  by  irritating  the  part  of  the  nervous  centres  from  which  the 
trunks  proceed,  so  long  as  the  latter  are  entire  ;  or  by  irritating  the 
portions  of  the  divided  trunks,  which  remain  in  connection  with  the 
electric  organs ;  or  even  by  irritating  portions  of  the  electric  organs 
themselves,  when  separated  from  the  nervous  centres. — In  all  these 
respects,  there  is  a  strong  analogy  between  the  action  of  the  nerves  on 
the  Electric  organs,  and  their  action  on  the  Muscles.  And  as  the 
latter  contract  by  their  own  inherent  powers,  when  stimulated  by  nerv- 
ous influence,  so  does  there  seem  reason  to  believe,  that  the  evolution 
of  Electricity  takes  place  from  some  peculiar  changes  in  the  electric 
organs,  of  which  changes  the  agency  of  the  nerves  is  one  of  the  con- 
ditions. To  the  idea  that  the  nervous  centres  produce  the  electricity, 
that  the  nervous  trunks  convey  it,  and  that  the  electric  organs  serve 
merely  to  store  it  up,  there  are  several  objections,  and  especially 
these ; — that  there  is  nothing  whatever  in  the  structure  of  the  brains 
of  the  Electrical  Fishes,  that  marks  them  out  as  essentially  differ- 
ent from  those  of  the  species  to  which  they  are  otherwise  allied ; — 
that  the  power  of  the  nerve-trunk,  in  conveying  the  requisite  stimu- 
lus to  the  electric  organs,  is  destroyed  as  completely  by  tying,  as  by 
dividing  the  trunk,  which  would  not  be  the  case  if  the  nervous 


442  MANIFESTATIONS  OF  ELECTRICITY. 

agency  were  itself  of  the  nature  of  ordinary  electricity  (§  396); — 
and  that  electric  manifestations  may  be  procured  from  the  electric 
organs,  by  stimuli  applied  to  themselves,  after  the  complete  severance 
of  their  connection  with  the  brain, — ^just  as  muscles  may  be  thrown 
into  contraction  by  direct  stimulation,  under  the  same  circumstances 
(§348). 

775.  It  is  another  interesting  point  of  analogy  between  the  action 
of  Muscles,  and  that  of  the  Electrical  organs,  that  the  former  (as  is 
now  fully  proved  by  the  elaborate  and  exact  researches  of  Matteuci), 
is  attended  with  electrical  disturbance.  In  any  fresh  vigorous  mus- 
cle, in  a  state  of  passive  or  tonic  contraction,  there  is  a  continual 
electric  current  from  the  interior  to  the  exterior,  sufficient  to  excite 
the  leg  of  a  frog  to  energetic  contraction,  when  its  nerve  is  so  ap- 
plied to  the  muscle,  as  to  receive  the  influence  of  this  current.  And 
a  much  more  powerful  current  is  produced,  when  the  muscle  is  thrown, 
by  a  stimulus  applied  to  its  own  nerve,  into  a  state  of  energetic  con- 
traction. The  explanation  of  the  constant  direction  of  the  current, 
from  the  interior  towards  the  exterior  of  the  muscle,  seems  to  be,  that 
the  changes  connected  with  the  nutrition  and  disintegration  of  the 
muscular  tissue  go  on  more  energetically  in  its  interior,  than  they  do 
nearer  its  surface,  where  the  proper  muscular  fibres  are  mingled  with 
a  large  proportion  of  areolar  and  tendinous  substance. 

776.  It  has  also  been  shown  that  there  exists  in  the  Frog,  during 
its  whole  life,  a  continual  current  of  Electricity,  passing  from  its 
extremities  towards  its  head.  The  conditions  on  which  this  current 
depends  do  not  seem  very  evident;  and  as  it  has  been  detected  in 
no  other  animal,  it  has  been  termed  the  courant  propre,  or  peculiar 
current,  of  the  Frog.  It  bears  this  curious  analogy  to  the  electric 
discharges  of  Fishes;  that  it  is  not  manifested,  if  the  connection  be 
made  between  corresponding  points  of  the  opposite  sides;  but  that  it 
shows  itself,  when  the  communication  is  made  between  points  higher 
or  lower  in  the  body,  whether  on  the  same  or  on  opposite  sides. 

777.  Manifestations  of  Electricity  may  be  produced,  in  most  animals 
having  a  soft  fur,  by  rubbing  the  surface,  especially  in  dry  weather ; 
this  is  a  fact  sufficiently  well  known  in  regard  to  the  domestic  Cat. 
Some  individuals  of  the  Human  race  exhibit  spontaneous  manifesta- 
tions of  electricity,  which  are  occasionally  of  very  remarkable  power. 
There  are  persons,  for  instance,  who  scarcely  ever  pull  off  articles  of 
dress,  which  have  been  worn  next  their  skin,  without  sparks  and  a 
crackling  noise  being  produced,  especially  in  dry  weather.  This  is 
partly  due,  however,  to  the  friction  of  these  materials  with  the  surface, 
and  with  each  other.  But  the  case  of  a  lady  has  been  recently  put 
on  record,  who  was  for  many  months  in  an  electric  state  so  different 
from  that  of  surrounding  bodies,  that,  whenever  she  was  but  slightly 
insulated  by  a  carpet  or  other  feebly-conducting  medium,  sparks 
passed  between  her  person  and  any  object  which  she  approached. 
When  she  was  most  favourably  circumstanced,  four  sparks  per  minute 
would  pass  between  her  finger  and  the  brass  ball  of  a  stove  at  a  dis- 


f  I 


REPRODUCTION.  443 

tance  of  IJ  inch.  Various  experiments  were  tried,  with  the  view  of 
ascertaining  if  the  Electricity  was  produced  by  the  friction  of  articles 
of  dress ;  but  no  change  in  these  seemed  to  modify  its  intensity.  From 
the  pain  which  accompanied  the  passage  of  the  sparks,  this  condition 
was  a  source  of  much  discomfort  to  the  subject  of  it. 


CHAPTER  XL 

OF    REPRODUCTION. 

1 .  General  View  of  the  J\*ature  of  the  Process. 

778.  There  is  no  one  of  the  functions  of  living  beings,  that  dis- 
tinguishes them  in  a  more  striking  and  evident  manner  from  the  inert 
bodies  which  surround  them,  than  the  process  of  Reproduction.  By 
this  function,  each  race  of  Plants  and  Animals  is  perpetuated;  whilst 
the  individuals  composing  it  successively  disappear  from  the  surface 
of  the  earth,  by  that  death  and  decay  which  are  the  common  lot  of  all. 
There  are  certain  tribes,  in  which  the  death  of 

the  parent  is  necessary  for  the  liberation  of  the  ^'^-  ^-^■ 

germs,  from  which  a  new  race  is  to  spring  up. 

This  is  the   case,  for  example,  in  some  of  the 

simplest  Cellular  Plants;  in  which  every  cell 

lives  for  itself  alone,  and   performs  its  w^hole 

series  of  vital  operations  independently  of  the 

rest;  and  in  which  the  process  of  reproduction 

consists  in  the  rupture  of  the  parent-cell,  and  the 

emission  of  the  contained  reproductive  particles, 

every  one   of  which  is  capable  of  developing        simple isoiat<dceiiscon- 

itself  into   a  new  cell,  resembling  that   of  its      Ss".^  reproductive  moie- 

parent  and  capable  of  going  through  the  same 

series  of  changes  (§  31).     But  as,  in  more  complex  organisms,  we 

find  certain  cells  set  apart  for  Absorption,  others  for  Secretion,  &c., 

so  do  we  find  a  particular  group  of  cells  set  apart  for  Reproduction ; 

and  these   go  through  a  series  of  changes   analogous  to  those  juvSt 

described,  yet  without  interfering  with  the  general  life  of  the  structure. 

779.  Among  many  of  the  lower  Animals,  a  multiplication  of  indi- 
viduals takes  place  by  a  process  that  closely  resembles  the  budding  of 
Plants ;  this  must  be  regarded,  however,  not  as  a  proper  act  of  Repro- 
duction, but  as  a  modification  of  the  ordinary  Nutritive  process.  The 
same  may  be  said  of  the  powers  of  reparation,  which  every  Animal 
body  possesses  in  a  greater  or  less  degree,  but  which  are  by  far  the 
most  remarkable  among  the  lower  tribes  ;  for  when  an  entire  member 
is  renewed  (as  in  the  Star-fish),  or  even  the  whole  body  is  regenerated 


444  SIMPLEST  FORMS  OF  REPRODUCTIVE  PROCESS. 

from  a  small  fragment  (which  is  the  case  in  many  Polypes),  it  is  by  a 
process  exactly  analogous  to  that  which  is  concerned  in  the  repara- 
tion of  the  simplest  wound  in  our  own  bodies,  and  which,  as  already 
explained  (§  636),  is  but  a  modification  of  the  process  that  is  con- 
stantly renewing,  more  or  less  rapidly,  every  portion  of  their  fabric. 
The  essential  character  of  the  special  function  of  Reproduction,  con- 
sists in  the  entire  separation  of  certain  germs  from  the  parent  structure ; 
which  are  capable,  by  their  own  inherent  powers,  of  developing 
themselves  into  new  individuals:  the  only  conditions  requisite,  being 
a  proper  supply  of  nutriment,  and  a  certain  amount  of  warmth.  In 
the  case  of  the  simple  Cellular  Plants  just  now  adverted  to,  the  germs, 
when  set  free  from  the  parent-cell,  are  thrown  at  once  upon  their  own 
resources,  and  draw  from  the  surrounding  elements  the  materials  of 
their  growth  and  development  (§  32).  But  in  the  higher  Plants,  we 
find  not  only  a  set  of  germ-preparing  organs,  or  reproductive  cells 
(the  pollen-grains),  but  also  a  set  of  germ-nourishing  organs  (the 
ovules);  into  which  the  reproductive  granules  are  received,  and  in 
which  they  are  supplied  with  nutriment  previously  elaborated  by  the 
parent,  that  serves  to  nourish  them  during  the  early  stages  of  their 
development. 

780.  This  is  the  universal  method  in  which  the  Reproductive  pro- 
cess is  effected  in  Animals ;  the  concurrence  of  two  sets  of  organs 
being  always  necessary, — the  germ-preparing  organs,  or  seminal  cells; 
and  the  germ-nourishing  organs,  or  ova.  These  may  be  united  in  the 
same  individual,  as  they  are  in  most  plants;  and  the  ova  may  be  fer- 
tilized from  the  seminal  cells  of  the  same  being; — as  happens  in  some 
of  the  lowest  tribes  of  MoUusca.  Or,  the  two  sets  of  organs  being 
present  in  each  individual,  it  may  not  be  capable  of  self-impregnation; 
but,  in  the  congress  of  two  individuals,  each  impregnates,  and  is  im- 
pregnated by  the  other ; — as  may  be  observed  in  the  Snail,  and  many 
of  the  higher  Mollusks.  Or  the  sexes  may  be  altogether  distinct ; 
one  individual  possessing  only  the  male  or  germ-preparing  organs ; 
and  the  other  the  female,  or  germ-nourishing  apparatus. 

781.  The  early  Development  of  Animals  may  be  so  much  better 
understood,  when  the  general  history  of  that  of  Plants  is  compre- 
hended, that  it  is  desirable  here  to  give  an  outline  of  the  latter  sub- 
ject.— Where,  as  in  the  simplest  Cellular  Plants,  each  individual 
consists,  even  in  its  adult  state,  but  of  a  single  cell,  the  development 
of  one  of  the  reproductive  granules  into  the  complete  cell  constitutes 
the  whole  history  of  its  growth.  In  other  cases,  however,  w^e  have 
an  extension  of  the  original  structure  by  a  process  of  budding;  so 
that,  from  the  first-formed  cell,  a  cluster,  or  filament,  may  be  pro- 
duced, according  to  the  mode  in  which  this  budding  takes  place. 
Thus  it  may  occur,  as  in  Palmella,  very  much  in  the  manner  of  or- 
dinary Cartilage-cells,  (§  267,  Fig.  37,)  so  as  to  produce  a  cluster  of 
2,  4,  8  or  more  ;  or  it  may  proceed  in  a  linear  direction,  as  in  Carti- 
lage-cells near  the  ossifying  surface,  (Fig.  48,)  so  that  a  filament  is  the 
result,  as  the  ordinary  ConfervcB.     Now  if  the  cells  of  one  of  the  sim- 


REPRODUCTIVE  PROCESS  IN  PLANTS.  445 

pie  Confervse,  which  is  composed  of  single  rows,  bud  out  laterally,  as 
well  as  longitudinally,  a  leaf-like  expansion  is  formed,  like  that  of 
the  Sea-weeds.  This  simple  organ  has  the  power  of  performing  the 
functions  of  absorption,  digestion,  respiration,  &c.,  as  well  as  that  of 
reproduction  ;  and  as  it  differs  from  the  leaves  of  the  higher  plants 
(to  which  it  otherwise  bears  a  close  resemblance),  in  its  power  of  per- 
forming the  last-named  function,  it  is  distinguished  by  the  name  of 
frond. 

782.  Although,  in  the  highest  Cryptogamia,  the  character  of  the 
Plant  is  ultimately  to  become  very  different  from  this,  its  formation 
commences  in  precisely  the  same  manner;  so  that  the  young  Fern, 
which  is  afterwards  to  send  a  w^oody  stem  and  beautifully-formed 
leaves  into  the  air,  and  to  transmit  its  solid  roots  deep  into  the  ground, 
might  be  readily  mistaken  for  an  humble  Liverwort,  whose  frond  is 
not  destined  to  raise  itself  from  the  ground,  but  creeps  along  its  sur- 
face, and  obtains  its  nourishment  by  the  slight  fibres  which  insinuate 
themselves  into  the  soil.  In  both  cases,  the  primary  frond  is  evolved, 
in  a  precisely  similar  manner,  by  the  budding  of  the  original  cell; 
but  the  Liverwort  remains  upon  the  lower  grade,  beyond  which  it  is 
never  destined  to  pass, — the  primary  frond  being,  in  that  class,  the 
permanent  plant ;  w^hilst  in  the  Fern,  the  primary  frond  is  a  tempo- 
rary organ  merely,  the  purpose  of  which  is  to  obtain  and  elaborate 
the  nutriment,  that  is  destined  for  the  evolution  of  the  permanent 
structure.  It  is  from  the  centre  of  this  leafy  expansion,  that  the  true 
stem  and  roots  of  the  Fern  are  subsequently  put  forth  ;  and  the  whole 
of  the  primary  frond  decays  away,  as  soon  as  the  first  true  leaf  has 
unfolded  itself. 

783.  Although  the  embryo  of  the  Flowering  Plant  is  developed 
under  different  conditions, — that  is,  at  the  expense  of  the  nutriment 
provided  for  it  in  the  seed,  within  which  it  is  contained, — yet  the 
history  of  its  growth  is  essentially  the  same.  The  mass  of  cells,  which 
originates  from  the  pollen-granules  that  fertilize  the  ovule,  does  not 
at  first  take  the  form  which  the  young  plant  is  afterwards  to  present ; 
but  spreads  itself  out  into  a  single  or  double  cotyledon^  which  is  a 
leaf-like  expansion,  closely  resembling  the  primary  frond  of  the  Fern. 
It  is  by  this  organ,  that  the  nourishment  provided  in  the  ovule  is  ab- 
sorbed and  prepared  for  the  development  of  the  young  plant ;  the 
permanent  fabric  of  which,  even  when  the  seed  is  mature,  forms  but 
a  very  small  proportion  of  it.  The  development  of  the  permanent 
structure  takes  place  rapidly,  however,  during  the  process  of  germi- 
nation; in  which  all  the  nourishment  contained  in  the  seed  is  pre- 
pared for  the  embryo  by  the  cotyledons  ;  these  serving  the  purpose  of 
leaves,  until  the  stem  and  roots  have  been  developed,  and  the  true 
leaves  unfolded.  By  the  time  that  this  store  has  been  exhausted,  the 
development  of  the  embryo  has  advanced  sufficiently  far,  to  enable  it 
to  support  itself;  and  the  cotyledons  then  decay  away. 

784.  Thus  we  see  that  even  the  highest  Plants  have  to  pass  through 
the  conditions,  which  are  permanently  shown  in  the  lower;  and  that 


446 


REPRODUCTION  IN  ANIMALS.— ACTION  OF  MALE. 


the  parts  which  are  first  formed,  are  destined  for  a  temporary  purpose 
only.  We  shall  find,  in  tracing  the  history  of  the  development  of 
Animals,  that  exactly  the  same  general  fact  may  be  observed,  in  even 
a  higher  degree; — the  number  of  different  stages  being  greater;  and 
an  even  larger  proportion  of  the  parts  first  formed,  in  the  embryo  of 
the  higher  tribes,  having  a  merely  temporary  purpose,  and  being 
destined  to  an  early  decay,  as  soon  as  the  more  permanent  portions  of 
the  fabric  have  been  evolved. 


Fig.  129. 


2.  Jiction  of  the  Male, 

785.  The  share  in  the  Reproductive  function,  which  belongs  to 
the  Male  Sex,  essentially  consists  in  the  formation  and  liberation  of 
the  reproductive  particles.     These  are  prepared  within  peculiar  cells, 

as  already  described  (§  240) ;  and  the 
cells  are  either  scattered  through  the 
soft  parenchyma  of  the  body,  as  hap- 
pens among  some  of  the  lowest  ani- 
mals ;  or  they  are  confined  to  certain 
parts  of  it,  as  in  those  a  little  more 
elevated  in  the  scale ;  or  they  are 
formed  within  follicles  or  tubes,  clus- 
tered together  into  an  organ  of  a  gland- 
ular character,  known  as  the  Testis. 
Such  an  organ  is  found  in  all  Insects 
and  Mollusca ;  as  well  as  in  Verte- 
brated  Animals.  In  the  first  of  these 
classes,  it  is  formed  on  the  general 
plan  of  their  proper  glands  (§  720); 
being  usually  composed  of  tubes,  more 
or  less  elongated,  and  sometimes  ter- 
In  the  Mollusks,  on  the  other  hand, 
it  is  almost  invariably  composed  of  clusters  of  follicles.  In  either 
case,  the  seminal  cells  are  developed  within  the  tubes  or  follicles,  as 
are  the  ordinary  secreting  cells  of  the  Liver  or  Kidney  within  the 
tubes  or  follicles  of  those  glands ;  and  their  contents  are  discharged 
by  an  excretory  duct,  which  terminates  in  an  organ  that  conveys  them 
out  of  the  body,  either  emitting  them  into  the  surrounding  water  (as 
happens  with  many  Mollusca),  or  depositing  them  within  the  body  of 
the  female.  It  is  curious  that,  in  some  of  the  lowest  Fishes,  we  should 
return  to  one  of  the  simplest  conditions  of  this  organ, — a  mass  of  vesi- 
cles, without  an  excretory  duct.  In  these  cases,  the  secretion  formed 
within  the  vesicles  escapes,  by  their  rupture,  into  the  abdominal 
cavity ;  whence  it  passes  out  by  openings  that  lead  directly  to  the 
exterior. 

786.  The  Testis  in  Man  is  formed,  in  every  essential  particular, 
upon  the  plan  of  the  ordinary  Glands.  It  consists  of  several  distinct 
lobules,  separated  by  processes  of  the  fibrous   envelop,  or  tunica 


Formation  of  Spermatozoa  within  semi- 
nal cells  :— a,  ihe  original  nucleated  cell; 
b.  the  same  enlarged,  with  the  formation  of 
the  Spermatozoa  in  progress ;  c.  the  Sper- 
matozoa nearly  complete,  but  still  enclosed 
within  the  cell. 


minating  in  enlarged  follicles. 


STRUCTURE  OF  THE  TESTIS. 


447 


Fig.  130. 


albuo^inea,  which  pass  down  between  them  ;  and  each  lobule  consists 
of  a  mass  of  convoluted  tubuli  seminiferi,  through  which  blood-ves- 
sels are  minutely  distributed.  The 
diameter  of  these  tubuli  is  tolerably  uni- 
form ;  being,  when  thev  are  not  over- 
distended,  from  l-195th  to  1- 170th  of 
an  inch.  They  form  frequent  anasto- 
moses with  each  other ;  and  on  this 
account  it  is  difficult  to  trace  out  their 
free  or  caecal  extremities.  The  tubuli 
of  each  testis  discharge  their  contents 
into  an  efferent  duct,  the  Vas-deferens; 
and  by  this  the  product  is  conveyed 
into  the  Vesicula  seminalis  on  each 
side,  which,  like  the  gall-bladder  and 
Urinary  bladder,  serves  to  store  up  the 
secretion  until  the  proper  time  for  dis- 
charging it.  The  product  of  the  action 
of  the  Testis  consists  of  a  fluid,  through 
which  the  Spermatozoa  are  diffused, — 
these  last  bodies  being  usually  set  free 
by  the  rupture  of  the  seminal  cells  be- 
fore they  leave  the  tubuli  of  the  testis. 
It  is  difficult  to  determine  the  precise 
characters  of  the  fluid  portion  of  the 
secretion ;  as  this  is  mingled  with  other 
secretions  (such  as  that  of  the  Prostate 
gland,  and  of  the  mucous  lining  of 
the  Vesiculse  seminales  and  spermatic 
ducts)  before  it  is  emitted.  And  an  exact  analysis  is  not  of  much 
consequence ;  since  there  can  be  no  doubt  that  the  peculiar  powers 
of  the  fluid  depend  upon  the  Spermatozoa.  It  may  be  stated,  how- 
ever, that  the  Spermatic  fluid  has  an  alkaline  reaction,  and  that  it 
contains  albumen,  together  with  a  peculiar  animal  principle  termed 
Spermatine  ;  and  that  it  also  includes  saline  matter,  consisting  chiefly 
of  the  muriates  and  phosphates,  especially  the  latter,  which  form  crys- 
tals when  the  fluid  has  stood  for  some  little  time. 

787.  The  minute  filamentous  bodies  set  free  by  the  rupture  of  the 
spermatic  cells,  are  distinguished  by  their  power  of  spontaneous  move- 
ment, which  occasioned  them  to  be  long  regarded  as  proper  Animal- 
cules. It  is  now  clear,  however,  from  the  history  of  their  develop- 
ment, as  well  as  from  other  considerations,  that  they  cannot  be  justly 
regarded  in  this  light;  and  that  they  are  analogous  to  the  reproductive 
particles  of  Plants,  which,  in  many  cases,  exhibit  a  spontaneous  mo- 
tion of  extraordinary  activity,  after  they  have  been  set  free  from  the 
parent  structure.  The  human  Spermatozoon  consists  of  a  little  oval 
flattened  body,  from  the  l-600th  to  the  l-800th  of  a  line  in  length; 
from  which  proceeds  a  filiform  tail  gradually  tapering  to  a  very  fine 


Anatomy  of  the  Testis : — 1,  1,  The  tu- 
nica albuginea.  2,  2.  The  mediastinum 
testis.  3,  3.  The  lobuli  testis.  4,  4.  The 
vasa  recta.  5.  The  rete  testis.  6.  The 
vasa  efferentia,  of  which  six  only  are 
represented  in  this  diagram.  7.  The  coni 
vasculosi,  constituting  the  globus  major  of 
the  epididymis.  8.  The  body  of  the  epi- 
didymis. 9.  The  globus  minor  of  the 
epididymis.  10.  The  vas  deferens.  11. 
The  vasculum  aberrans. 


448  FORMATION  OP  SEMINAL  SECRETION. 

point,  of  l-50th  or  at  most  l-40th  of  a  line  in  length.  The  whole  is 
perfectly  transparent ;  and  nothing  that  can  be  called  structure  can  be 
satisfactorily  distinguished  within  it.  The  movements  are  principally 
excited  by  the  undulations  of  the  tail ;  which  give  a  propulsive  action 
to  the  body.  They  may  continue  for  many  hours  after  the  emission 
of  the  fluid;  and  they  are  not  checked  by  its  admixture  with  other 
secretions,  such  as  the  urine  and  the  prostatic  fluid.  When  the  semi- 
nal fluid  remains  in  contact  with  a  living  surface  (as  when  deposited 
in  the  generative  organs  of  the  female)  the  Spermatozoa  may  retain 
their  vitality  for  some  days  ;  and  an  instance  has  already  been  referred 
to  (§  240),  in  which  the  later  stages  of  the  development  of  the  Sper- 
matozoa actually  take  place  in  this  situation, — the  seminal  fluid 
emitted  by  the  male  (among  many  Crustacea)  not  containing  any 
Spermatozoa  completely  formed,  but  numerous  spermatic  cells,  which 
undergo  the  remainder  of  their  development,  and  then  rupture  and 
set  free  their  contents,  within  the  oviducts  of  the  female. 

788.  The  power  of  procreation  does  not  exist  in  the  Human  Male 
(except  in  rare  cases)  until  the  age  of  from  14  to  16  years;  at  which 
epoch,  the  sexual  organs  undergo  a  much  increased  development ;  and 
the  instinctive  desire,  which  leads  to  the  use  of  them,  is  awakened  in 
the  mind.  From  that  time,  to  an  advanced  age,  the  procreative  power 
remains,  in  the  healthy  state  of  the  system  ;  unless  it  be  exhausted  by 
excessive  use  of  it,  or  by  too  energetic  a  direction  of  the  mental  or 
corporeal  powers  to  some  other  object.  The  formation  of  Seminal 
fluid  being,  like  the  proper  acts  of  Secretion,  very  much  influenced  by 
conditions  of  the  nervous  system,  is  increased  by  the  continual  direc- 
tion of  the  mind  towards  objects  which  arouse  the  sexual  propensity; 
and  thus,  if  sexual  intercourse  be  very  frequent,  a  much  larger  quan- 
tity of  the  fluid  will  be  produced,  than  if  it  is  more  rarely  emitted, 
although  the  amount  discharged  on  each  occasion  will  be  less.  The 
formation  of  this  product  is  evidently  a  great  tax  upon  the  corporeal 
powers;  and  it  is  a  well-known  fact,  that  the  highest  degree  of  bodily 
and  mental  vigour  is  inconsistent  with  more  than  a  very  moderate 
indulgence  in  sexual  intercourse ;  whilst  nothing  is  more  certain  to 
reduce  the  powers,  both  of  body  and  mind,  than  excess  in  this  respect. 

789.  It  may  be  stated  as  a  general  law,  prevailing  equally  in  the 
Vegetable  and  Animal  kingdoms, — that  the  development  of  the  indi- 
vidual, and  the  reproduction  of  the  species,  stand  in  an  inverse  ratio 
to  each  other.  We  have  seen  that,  in  many  organized  beings,  the 
death  of  the  parent  is  necessary  to  the  production  of  a  new  generation  ; 
and  even  in  numerous  species  of  Insects,  it  follows  very  speedily  upon 
the  sexual  intercourse.  It  is  a  curious  fact,  that  Insects  which  usu- 
ally die,  the  male  almost  immediately  after  the  act  of  copulation, 
and  the  female  very  soon  after  the  deposition  of  the  eggs,  may  be 
kept  alive  for  many  weeks  or  even  months,  by  simply  preventing 
their  copulation.  And  there  can  be  no  doubt,  that,  in  the  Human 
race,  early  death  is  by  no  means  an  unfrequent  result  of  the  excessive 
or  premature  employment  of  the  genital  organs ;  and  where  this  does 


DEPENDENCE  OF  ANIMAL  EMBRYO  ON  FEMALE  PARENT.   449 

not  produce  an  immediately  fatal  result,  it  lays  the  foundation  of  future 
debility,  that  contributes  to  produce  any  forms  of  disease  to  which 
there  may  be  a  constitutional  predisposition,  especially  those  of  a 
Scrofulous  nature. 

790.  The  emission  of  the  Spermatic  fluid  is  an  act  of  a  purely  refiex 
nature;  the  Will  having  no  power  either  to  efTect  or  to  restrain  it. 
The  stimulus  is  given  by  the  friction  of  the  surface  of  the  Glans  Penis 
against  the  rugous  walls  of  the  Vagina;  the  sensibility  of  the  organ 
being  at  the  same  time  much  increased,  by  the  determination  of  blood 
to  it.  The  impression  is  at  last  sufficiently  strong  to  produce,  through 
the  medium  of  the  lower  part  of  the  Spinal  cord,  (which  is  the  gangli- 
onic centre  of  the  circle  of  afferent  and  efferent  nerves  connected  with 
this  organ,)  a  reflex  contraction  of  the  muscles  surrounding  the  vesi- 
culse  seminales.  These  receptacles  discharge  their  contents  (which 
consist  partly  of  the  Spermatic  fluid,  and  partly  of  a  secretion  of  their 
own),  into  the  Urethra ;  and  from  this  they  are  expelled  with  some 
degree  of  force  and  with  a  kind  of  spasmodic  action,  by  its  own 
Compressor  muscles.  Although  the  sensations  concerned  in  this  act 
are  ordinarily  most  acutely  pleasurable,  yet  there  appears  to  be  suffi- 
cient evidence  that  they  are  by  no  means  essential  to  its  performance; 
and  that  the  impression  conveyed  to  the  Spinal  cord  may  excite  the 
contraction  of  the  Ejaculator  muscles,  like  other  reflex  operations,, 
without  producing  sensation  (§  394). 

3.  Action  of  the  Female. 

791.  As  it  is  the  office  of  the  Male  to  prepare  the  germ  of  the 
future  being,  and  then  to  set  it  free,  so  is  it  the  part  of  the  Female  to 
receive  this  germ,  and  to  supply  it  with  the  materials  for  its  develop- 
ment, up  to  the  condition  in  w^hich  it  can  support  its  own  life.  The 
mode  in  which  this  is  accomplished,  is  essentially  the  same  with  that, 
in  which  the  process  is  effected  in  Plants.  In  certain  parts  of  the 
female  structure  are  developed  peculiar  bodies  termed  oi;a;  which, 
contain  a  store  of  nutriment,  adapted  to  supply  the  wants  of  the  germ. 
The  reproductive  particles  find  their  way  into  these,  and  begin  to- 
grow  at  the  expense  of  the  materials  which  they  meet  with  in  their 
interior.  This  may  enable  the  embryo  to  develop  itself,  without  any 
further  assistance  (save  a  warm  temperature),  into  the  form  it  is  per- 
manently to  assume  ;  as  in  the  case  of  Birds  and  Reptiles,  which  do' 
not  come  forth  from  the  investments  of  the  e^^^  until  they  have  at- 
tained the  form  characteristic  of  the  group  to  which  they  belong.  Or 
it  may  only  serve  for  the  early  part  of  the  process  ;  and  one  of  two 
methods  may  then  be  employed  to  complete  it.  Either  a  new  con- 
nection is  formed  between  the  parent  and  embryo,  by  which  the 
former  continues  to  supply  the  latter  with  nutriment,  more  directly 
from  its  blood  ;  as  is  the  rase  with  Mammalia — or  the  embryo  issues 
from  the  egg,  in  a  condition  very  unlike  that  which  it  is  permanently 
to  attain,  but  in  a  form  which  enables  it  to  acquire  its  own  nourish- 

29 


450  DEVELOPMENT  OF  OVA  IN  OVARIUM. 

ment,  and  to  pass  through  the  latter  stages  of  its  evolution  quite  inde- 
pendently of  any  assistance  from  its  parent ;  this  is  the  case  with  a 
large  proportion  of  the  Invertebrata. 

792.  Sometimes  the  permanent  form  of  the  latter  is  elaborated,  as 
it  were,  out  of  the  temporary,  by  the  gradual  development  of  new 
parts ;  as  happens  in  most  of  the  Worm  tribe, — the  animal,  at  the 
time  of  its  first  emersion  from  the  egg,  possessing  but  a  few  segments, 
or  even  but  a  single  one  ;  but  afterwards,  by  the  progressive  develop- 
ment of  new  segments,  to  the  number  in  some  instances  of  several 
hundreds,  acquiring  a  great  length.  In  other  cases,  there  is  a  com- 
plete metamorphosis  or  change  of  form  ;  the  animal  at  its  emersion 
from  the  egg,  not  merely  having  an  aspect  which  is  entirely  different 
from  that  which  it  is  ultimately  to  present,  but  possessing  organs 
which  it  is  afterwards  to  lose.  Thus  the  Frog  emerges  in  the  state  of 
a  Fish  ;  and  in  this,  its  Tadpole  condition,  it  breathes  by  gills,  swims 
by  its  tail,  and  has  all  the  essential  characters  of  the  class  below  its 
own.  Certain  of  its  organs  gradually  disappear  altogether,  whilst 
others  are  as  gradually  developed;  and  in  this  manner  the  temporary 
Fish  is  converted  into  the  permanent  Reptile.  The  metamorphosis  is 
even  more  striking  in  Insects ;  which  come  forth  from  the  egg  as 
"Worms ;  and  which  attain  their  complete  form  by  what  appears  to  be 
a  sudden  change, — this  change  being  really,  however,  of  a  very  gra- 
dual character,  the  organs  characteristic  of  the  perfect  Insect  being 
slowly  developed,  during  the  preceding  state  of  quiescence  which 
usually  characterizes  the  life  of  the  Chrysalis,  but  being  displayed 
and  brought  into  use  only  when  the  Chrysalis-skin  is  thrown  off. 
Thus  the  whole  life  of  the  Insect,  up  to  this  last  change,  may  be  re- 
garded as  one  of  embryonic  development ;  and  the  same  may  be  said 
of  the  condition  of  the  Frog,  up  to  the  time  w^hen  its  permanent 
organs  are  fully  evolved. 

793.  The  Ova,  like  the  seminal  cells,  are  scattered  through  the  soft 
parenchyma  of  the  body,  in  animals  of  the  lowest  class;  but  they  are 
more  commonly  developed  in  certain  distinct  portions  of  the  fabric  ; 
being  sometimes  formed  in  the  midst  of  solid  masses  of  areolar  or 
cellular  texture  ;  whilst  in  other  instances  they  are  developed,  like 
the  spermatic  cells,  in  the  interior  of  tubes  and  vesicles  resembling 
those  of  glands,  and  furnished  with  an  excretory  duct.  The  latter 
condition  obtains  in  the  greater  proportion  of  the  higher  In  vertebrated 
animals,  and  in  some  Fishes  ;  but  in  the  Vertebrated  classes  we  return 
to  the  type  w^hich  characterizes  the  egg-producing  organs  in  many 
Zoophytes, — namely,  the  development  of  the  egg  in  the  midst  of  a 
mass  of  solid  parenchyma,  from  which  it  gradually  makes  its  way,  to 
escape  into  the  abdominal  cavity.  The  Ovarium  of  the  Mammal, 
Bird  or  Reptile,  as  well  as  that  of  most  Fishes,  differs  entirely,  there- 
fore, from  that  of  the  Invertebrata  ;  for  the  latter  have  all  the  essen- 
tial characters  of  true  glands  ;  whilst  the  former  are  nothing  else  than 
masses  of  parenchyma,  copiously  supplied  with  blood-vessels,  and 
having  dispersed  through  their  substance  certain  peculiar  cells,  termed 


STRUCTURE  AND  DEVELOPMENT  OF  OVUM.        451 

ovisacs^  within  which  the  ova  are  developed.  In  order  that  the  latter 
may  be  set  free,  not  only  must  the  ovisac  itself  burst  (like  parent-cells 
in  general),  but  the  peculiar  tissue,  and  the  envelops,  of  the  ovarium 
must  likewise  give  way.  When  the  ova  thus  escape  into  the  ab- 
dominal cavity,  they  may  lie  there  for  some  time,  at  last  to  be  dis- 
charged through  simple  openings  in  its  walls,  as  happens  in  those 
Fishes  which  have  this  form  of  ovarium  ;  or  they  may  be  at  once 
received  into  the  trumpet-shaped  expansions  of  tubes,  that  shall  con- 
vey them  to  these  orifices.  These  tubes  are  termed  oviducts,  in  com- 
mon with  the  excretory  ducts  of  the  glandular  ovaria  of  Invertebrated. 
animals  ;  for  their  function  is  the  same, — that  of  conveying  the  ova 
to  the  outlet  by  which  they  are  extruded  from  the  body.  They  are 
represented  in  Mammalia  by  the  Fallopian  tubes,  which  are  true  ovi- 
ducts ;  but  these  unite  and  enlarge  to  form  a  Uterine  cavity,  in  which 
the  embryo  may  be  retained,  whilst  it  is  receiving  the  further  assist- 
ance to  its  development,  in  the  manner  to  be  presently  explained. 
This  uterine  cavity  is  peculiar  to  the  Mammalia ;  but  there  are  many 
cases  among  the  lower  classes,  in  which  the  ovum  is  retained  within 
the  oviduct,  so  that  the  young  comes  into  the  world  alive  ;  and  a  few 
in  which,  during  this  delay,  it  receives  a  direct  supply  of  additional 
nourishment  from  the  fluids  of  its  parent. 

794.  The  essential  structure  of  the  ovule,  or  unfertilized  egg,  ap- 
pears to  be  the  same  in  all  animals.  It  consists  externally  of  a  mem- 
branous sac,  termed,  from  the  nature  of  its  contents,  the  yelk-bag. 
The  yelky  or  contained  fluid,  consists  chiefly  of  albumen  and  oil- 
globules  ;  and  it  is  this  substance,  which,  like  the  starchy  and  oily 
matter  laid  up  in  the  seed  of  the  Plant,  is  destined  to  afford  support 
to  the  embryo,  until  it  is  able  to  obtain  its  own  nutriment,  or,  as  in 
Mammalia,  forms  a  new  connection  with  the  parent.  Floating  in 
this  fluid  is  a  cell  of  peculiar  aspect,  termed  the  germinal  vesicle  ;  and 
upon  its  wall  is  a  very  distinct  nucleus,  termed  the  germinal  spot. — 
The  layer  of  albumen  surrounding  the  yelk,  and  termed  the  white  of 
the  Bird's  egg,  together  with  the  membrane  which  envelops  this  and 
forms  the  basis  of  the  shell,  are  not  added  until  after  the  ovum  has 
left  the  ovarium.  They  are  not  present  in  the  eggs  of  many  of  the 
lower  Invertebrata ;  these  consisting  merely  of  the  parts  which  are 
formed  within  the  ovarium. 

795.  The  structure  of  the  ovule  in  Mammals  differs  in  no  essential 
particular  from  that  just  described  ;  but  the  yolk  is  much  less  in 
amount,  than  in  the  ovules  of  Invertebrated  animals  ;  since  only  the 
very  earliest  stages  of  the  development  of  the  embryo  are  to  take 
place  at  its  expense.  We  shall  find  that  the  ovule,  after  leaving  the 
ovarium  and  receiving  the  fertilizing  influence,  becomes  enclosed, 
whilst  passing  through  the  Fallopian  tube,  with  a  layer  of  albumi- 
nous matter,  which  represents  the  white  of  the  Bird's  egg;  and  with 
an  additional  fibrous  envelop,  which  corresponds  with  the  membrane 
enveloping  the  latter.  This  fibrous  membrane,  termed  the  Chorion, 
afterwards    becomes    subservient,    however,    to    various    important 


452  PUBERTY.— MENSTRUAL  DISCHARGE. 

changes ;  by  means  of  which  the  ovum  is  again  brought  into  con- 
nection with  the  parent,  to  derive  from  the  blood  of  the  latter  the 
materials  requisite  for  the  continued  development  of  the  embryo. 
These  changes  will  be  described  hereafter  (§  811). 

796.  The  Ovisac  of  Mammalia  forms  the  inner  layer  of  what  is 
termed  the  Graafian  follicle^  after  the  name  of  its  discoverer ;  and 
instead  of  closely  enveloping  the  ovulum,  as  it  does  in  oviparous 
animals,  it  contains,  in  addition  to  it,  a  quantity  of  granular  matter, 
consisting  of  cells  arranged  in  membranous  layers,  together  with  fluid. 
Of  these  layers,  one  surrounds  the  ovulum,  and  is  termed  the  tunica 
granulosa;  another  lines  the  ovisac,  and  is  named  the  memhrana 
granulosa;  whilst,  to  certain  bands  passing  from  the  former  to  the 
latter,  and  suspending  the  ovule  (as  it  were)  in  the  cavity  of  the 
ovisac,  the  name  of  retinacula  h^s  been  given  by  their  discoverer, 
Dr.  Barry. — The  outer  layer  of  the  Graafian  follicle  is  formed  by  a 
thickening  and  condensation  of  the  surrounding  parenchyma. of  the 
ovarium  ;  and  it  is  quite  distinct  from  the  ovisac  which  it  envelops. 
It  is  extremely  vascular,  and  is  evidently  destined  to  afford  to  the 
structures  within  the  materials  for  their  development,  which  they  re- 
ceive and  appropriate  by  their  own  powers  of  absorption  and  assimi- 
lation. 

797.  The  Mammalian  Ovarium  may  be  seen,  even  in  the  foetal 
animal,  to  contain  immature  ova,  enclosed  within  their  ovisacs;  and 
the  several  parts  of  the  former  may  be  clearly  distinguished,  in  those 
which  are  in  the  more  advanced  stages  of  development.  It  appears 
that,  during  the  period  of  childhood,  there  is  a  continual  rupture  of 
the  ovisacs  (or  parent-cells),  and  a  discharge  of  ova,  at  the  surface  of 
the  ovarium  ;  but  these  ova  never  attain  so  high  a  degree  of  develop- 
ment, as  to  render  them  fit  for  impregnation.  Their  evolution  takes 
place  more  completely,  as  well  as  more  rapidly,  at  the  period  of 
puberty,  when  there  is  a  greatly  increased  determination  of  blood  to 
the  genital  organs,  and  a  correspondingly  augmented  energy  in  their 
nutritive  operations.  At  this  epoch,  the  parenchyma  of  the  ovarium 
is  crowded  with  ovisacs ;  which  are  still  so  minute,  that  in  the  Ox, 
according  to  Dr.  Barry's  computation,  a  cubic  inch  would  contain 
200  millions  of  them.  Some  of  those  nearest  the  surface,  however, 
are  continually  attaining  increased  development;  and  a  rupture  of 
some  of  the  Graafian  follicles,  and  a  discharge  of  ova  prepared  for 
impregnation,  from  the  exterior  of  the  ovarium,  thenceforth  take 
place,  with  more  or  less  tendency  to  periodicity,  during  the  whole 
time  that  the  female  is  in  a  state  of  aptitude  for  procreation. 

798.  In  the  Human  female,  the  period  of  Puberty  usually  occurs 
between  the  13th  and  16th  year.  The  dififerences  in  the  time  of  its 
advent  partly  depend  upon  individual  constitution,  and  partly  upon 
various  external  circumstances,  such  as  temperature,  habits  of  life,  &c. 
As  a  general  rule,  habitual  exposure  to  a  warm  atmosphere,  an  inert 
life,  sensual  indulgence,  and  circumstances  that  excite  the  sexual 
feelings,  favour  the  approach  of  Puberty ;  whilst  a  cold  climate  and 


^ 


MENSTRUAL  DISCHARGE.— MATURATION  OF  OVA.  453 

hardy  life  retard  it.  The  appearance  of  the  Catamenial  discharge 
usually  takes  place  whilst  the  evolution  of  the  genital  organs  is  in 
progress  ;  and  it  is  a  decided  indication,  when  it  occurs,  that  the 
aptitude  for  procreation  has  been  attained.  It  is  not  unfrequently 
delayed  much  longer,  however;  and  its  absence  is  by  no  means  to  be 
regarded  as  a  proof  of  inability  to  conceive.  The  Catamenial  secre- 
tion, which  proceeds  from  the  lining  membrane  of  the  Uterus,  seems 
to  consist  of  the  elements  of  Blood,  in  an  altered  condition.  It  con- 
tains a  considerable  amount  of  red  colouring  matter ;  but  the  albu- 
minous and  fibrinous  constituents  seem  to  be  present  in  smaller 
proportion  than  in  Blood.  The  coagulating  power  is  for  the  most 
part  wanting,  when  the  function  is  performed  in  a  healthy  manner  ; 
the  appearance  of  clots  being  an  indication  that  blood  is  escaping 
from  the  secreting  surface.  The  coagulation  of  the  fibrin  normally 
present  in  the  secretion,  appears  to  be  prevented  by  admixture  with 
the  vaginal  mucus  ;  but  when  an  increased  amount  is  poured  forth, 
this  admixture  is  not  sufficient  to  destroy  its  power  of  forming  a  clot. 
In  some  cases  of  difficult  Menstruation,  which  seem  to  depend  upon 
a  state  of  low  inflammation  in  the  Uterus,  the  fibrin  has  such  a  tend- 
ency to  become  organized,  as  to  form  shreds,  or  layers  of  false 
membrane,  which  sometimes  plug  up  the  os  uteri.  The  healthy 
Menstrual  secretion  is  remarkable  for  its  very  acid  character. 

799.  This  flux  of  altered  blood  from  the  lining  membrane  of  the 
Uterus,  is  not  confined  to  the  Human  female,  as  was  formerly  sup- 
posed ;  but  occurs  in  most  of  the  lower  Mammalia  in  the  state  of 
heat^  or  periodical  aptitude  for  procreation,  at  which  time  the  ova- 
rium contains  ova  ready  for  impregnation.  The  chief  peculiarity 
attending  its  appearance  in  the  Human  female,  is  its  regular  monthly 
return.  In  the  natural  condition  of  many  of  the  lower  Mammalia,  as 
in  Oviparous  animals,  the  period  of  heat  recurs  ai  some  one  time  of 
the  year, — usually  in  the  spring ;  or,  in  the  smaller  and  more  prolific 
species,  from  two  to  six  times.  And  in  those  which  have  undergone 
a  change  by  domestication,  the  recurrence  is  usually  irregular,  de- 
pending upon  various  circumstances  of  regimen,  temperature,  &c. 
The  general  analogy  between  the  Menstruation  of  the  Human  female 
and  the  heat  of  the  lower  Mammalia, — consisting  in  the  peculiar  apti- 
tude for  impregnation  which  then  exists,  in  consequence  of  the  matu- 
ration of  ova  in  the  ovarium, — cannot  now  be  questioned  ;  but  it 
appears  that,  in  the  Human  female,  ova  may  be  matured  and  impreg- 
nated at  any  part  of  the  period,  which  elapses  between  the  occur- 
rences of  the  Catamenial  discharge ;  though  it  is  certain  that  the  apti- 
tude for  conception  is  much  greater,  during  the  few  days  which 
precede  and  follow  the  menstrual  period,  than  at  any  intervening 
time.  The  duration  of  the  period  of  aptitude  for  procreation,  which 
is  marked  by  the  continued  appearance  of  the  Catamenia,  is  more 
limited  in  Women  than  in  Men  ;  usually  terminating  at  about  the 
45th  year.  It  is  sometimes  prolonged,  however,  for  ten  or  even  fif- 
teen years  longer ;  but  cases  are  rare,  in  which  women  above  50 


454  MATURATION  OF  OVA. 

years  of  age  have  borne  children.  There  is  usually  no  menstrual 
flow  during  pregnancy  and  lactation  ;  in  fact,  the  cessation  of  the 
Catamenia  is  usually  one  of  the  first  signs  indicating  that  conception 
has  taken  place.  It  is  by  no  means  uncommon,  however,  for  them 
to  appear  once  or  twice  subsequently  to  Conception  ;  and  their  ap- 
pearance during  Lactation,  especially  if  it  be  much  prolonged,  is  still 
more  frequent;  hence  it  might  be  inferred,  that  the  continuance  of 
Lactation  would  not  prevent  a  fresh  conception, — which  is  found  to 
be  true  in  practice. 

800.  We  shall  now  take  a  brief  survey  of  the  changes  which  occur 
in  the  Ovulum,  when  it  is  being  prepared  for  fecundation  ;  and  of  the 
principal  features  of  its  subsequent  development. — Up  to  the  period 
when  the  Ovule  is  nearly  brought  to  maturity,  it  remains  suspended 
in  the  centre  of  the  cavity  of  the  Ovisac  ;  but  it  then  begins  to  move 
towards  that  side  of  the  Graafian  follicle,  which  is  nearest  the  surface 
of  the  ovarium.  An  important  change  is  at  the  same  time  occurring 
in  the  Graafian  follicle  itself;  for  whilst  the  part  with  which  the  ovule 
comes  in  contact  gradually  thins  away,  the  outer  or  vascular  layer  of 
the  remainder,  especially  on  that  side  most  deeply  imbedded  in  the 
ovary,  becomes  much  increased  in  thickness ;  and  a  deposition  of 
fibrinous  matter  seems  to  take  place  at  that  part,  between  this  layer 
and  the  inner  layer  or  proper  ovisac.  This  fibrinous  matter  is  destined 
subsequently  to  become  more  or  less  completely  organized ;  receiv- 
ing vessels,  which  are  prolonged  into  it  from  its  enveloping  mem- 
brane: and  it  then  forms  the  corpus  luteum.  The  escape  of  the  ovule 
from  the  ovarium  involves  processes  which  are  essentially  the  same, 
whether  it  be  impregnated  or  not ;  but  the  subsequent  changes  difTer 
in  the  two  cases,  so  that  the  corpus  luteum  which  accompanies  the 
pregnant  state  is  a  much  more  highly  organized  body  than  that  which 
is  found  in  the  ovary  of  the  unimpregnated  female.  This  difference 
may  be  due  in  part  to  the  absence,  in  the  latter  case,  of  that  special 
determination  of  blood  to  the  genital  organs,  which  takes  place  in  the 
former. 

801.  When  the  ovule  is  being  thus  brought  near  the  surface  of  the 
Ovary,  a  series  of  remarkable  changes  takes  place  in  its  interior. 
The  yelk  becomes  filled  with  cells;  which,  after  passing  through 
several  .generations  (during  which  the  transparency  of  the  yelk  is 
much  interfered  with),  completely  disappear,  leaving  the  fluid  appa- 
rently in  the  same  condition  as  before.  This  process  of  cell-develop- 
ment in  the  substance  of  the  yelk,  continues  for  some  time  after 
fecundation  ;  and  it  probably  has  for  its  purpose,  to  prepare  the  mat- 
ter of  the  yelk  for  its  subsequent  functions ;  just  as  we  have  seen 
reason  to  believe,  that  the  albuminous  matter  of  the  chyle  is  ren- 
dered fit  for  the  nutrition  of  the  body,  by  the  development  of  floating 
cells  in  its  current  (§  213).  But  the  most  curious  changes  are  those, 
which  take  place  within  the  germinal  vesicle.  Though  previously 
in  the  centre  of  the  yelk,  it  now  moves  up  towards  one  side  of  it, 
and  becomes  flattened  against  the  yelk-bag.     At  the  same  time,  the 


FERTILIZATION  OF  OVA.  455 

edge  of  its  nucleus  begins  to  resolve  itself  into  a  ring  of  cells;  which 
sprout  forth,  as  it  were,  from  its  inner  wall,  into  its  cavity.  These 
cells  enlarge ;  and  another  ring  is  developed  nearer  the  centre  of  the 
nucleus,  pushing  the  former  one  outwards.  A  third  ring  is  next 
formed  internally  to  the  second  ;  and  a  similar  development  of  suc- 
cessive annuli  of  minute  cells,  one  within  another,  continues,  until 
the  whole  germinal  vesicle  is  filled  with  minute  cells ;  of  which  those 
constituting  the  outer  and  first  formed  rings  are  the  largest,  whilst 
those  forming  the  central  rings  are  very  minute.  The  centre  of  what 
was  the  germinal  spot  remains  transparent ;  and  into  this  the  germ 
finds  its  way  in  the  act  of  fertilization,  by  the  means  to  be  presently 
described.  All  these  cells,  like  those  of  the  yelk,  have  a  merely 
temporary  existence,  and  speedily  deliquesce  again  ;  and  their  func- 
tion appears  to  be,  to  prepare  the  contents  of  the  germinal  vesicle  for 
being  applied  to  the  nutrition  of  the  germ,  which  is  to  be  subsequently 
introduced  into  it. 

802.  By  the  changes  in  the  position  of  the  Ovulum  and  of  its  con- 
tained parts,  which  have  been  already  noticed,  the  germinal  vesicle 
is  brought  into  very  close  proximity  with  the  surface  of  the  Ovary. 
It  is  still  covered,  however,  by  the  peritoneal  coat  of  the  ovary;  by  a 
thin  layer  of  the  fibrous  substance  of  that  organ  ;  by  the  ovisac  ;  and 
by  the  yelk-bag,  which,  in  the  Mammalian  ovum,  is  known  as  the 
zona  pellucida.  The  three  former  of  these  envelops  gradually  thin 
away,  and  at  last  rupture,  and  give  passage  to  the  ovule;  which  thus 
escapes  from  the  surface  of  the  ovarium.  At  about  the  same  time,  a 
chink  or  fissure  is  formed  in  the  part  of  the  yelk-bag,  that  covers  the 
central  pellucid  space  of  the  germinal  spot ;  and  into  this  space  the 
fertilizing  influence  appears  to  be  introduced  ;  for  we  find  it  afterwards 
occupied  by  two  new  cells,  of  very  diflf'erent  appearance  from  the  rest, 
from  which  the  whole  of  the  embryonic  structure  is  subsequently  to 
be  developed. 

803.  Much  discussion  has  taken  place,  with  regard  to  the  exact 
point  at  which  the  fertilization  of  the  ovulum  takes  place  ;  but  this  does 
not  seem  to  be  a  matter  of  much  consequence,  as  we  find  the  order  of 
the  diflferent  steps  to  vary  considerably  in  diflferent  classes  of  animals. 
Thus  in  many  aquatic  Mollusca,  and  even  in  a  large  proportion  of 
the  class  of  Fishes,  there  is  no  act  of  copulation  whatever ;  but  the 
spermatic  fluid,  when  emitted  by  the  male,  is  diflfused  through  the 
water,  and  fertilizes  the  ova,  which  have  been  deposited  by  the 
female  in  his  neighbourhood.  In  the  Frog,  again,  and  in  other  Rep- 
tiles, the  spermatic  fluid  is  emitted  upon  the  ova,  at  the  time  that  they 
are  being  extruded  by  the  female.  In  many  Insects  and  Crustacea, — 
in  which  a  single  congress  often  serves  to  fertilize  many  thousand 
eggs,  the  deposition  of  which  occupies  a  period  of  several  weeks  or 
months, — the  spermatic  fluid  is  received  and  stored  up  in  a  saccular 
dilatation  of  the  oviduct  of  the  female,  which  is  termed  the  spermo- 
theca  ;  and  in  this  manner  it  serves  to  impregnate  the  ova,  as  they  are 
successively  developed,  and  are  conveyed  to  the  outlet  of  the  oviduct. 


456  EARLY  CHANGES  IN  FERTILIZED  OVUM. 

In  Birds,  we  find  that  ova  are  often  set  free  from  the  ovarium  in  a 
state  of  full  maturity,  but  without  fertilization ;  and  that  they  receive 
their  additional  layer  of  albumen  and  their  shelly  envelop,  in  passing 
down  the  oviduct,  so  as,  at  the  time  of  their  deposition,  to  differ  in 
no  obvious  particular  from  fertile  eggs.  It  is  doubtful,  in  regard  to 
Mammalia,  whether  the  act  of  fertilization  takes  place  before  the  ovum 
has  been  actually  discharged  from  the  ovisac,  or  subsequently  to  its 
finally  quitting  the  ovarium  and  being  received  into  the  Fallopian 
tube.  It  is  quite  certain  that  the  spermatozoa  frequently,  if  not  inva- 
riably, find  their  way  to  the  surface  of  the  ovary,  being  carried  thither 
by  their  own  spontaneous  movements ;  and  it  seems  on  the  whole 
most  probable,  that  the  fertilization  of  the  ova  usually  takes  place 
before  they  have  been  discharged  from  the  ovisac,  or  whilst  they  are 
still  in  the  commencement  of  the  Fallopian  tube.  It  is  not  unlikely 
that  the  place  of  the  act  of  fecundation  varies,  according  to  the  point 
at  which  the  ovule  and  the  seminal  fluid  first  come  into  contact, — 
which  may  depend  upon  the  degree  of  maturity  of  the  ova  at  the 
period  of  copulation. 

804.  Everything  indicates  that  the  contact  of  the  Spermatozoon 
with  the  Ovulum  is  the  one  thing  needful  in  the  act  of  fecundation  ; 
and  there  is  strong  reason  to  believe,  that  the  large  end  of  the  Sper- 
matozoon finds  its  way  into  the  fissure  just  described,  which  is  formed 
in  the  Zona  pellucida  ;  and  that  it  there  deposits  the  germs  of  the  two 
new  cells,  which  are  afterwards  seen  within  the  germinal  vesicle. 
We  have  seen  that  this  is  the  essential  nature  of  the  fecundating  pro- 
cess in  the  Flowering  Plant ;  the  reproductive  granules,  prepared 
within  the  pollen-cell,  being  conveyed  by  the  pollen-tube  within  the 
ovule,  where  they  speedily  develop  themselves  into  the  first  cells  of 
the  embryonic  structure.  The  manner  in  which  the  reproductive 
germs  of  the  Animal  find  their  way  to  the  ovary,  is  different,  as  we 
have  seen  ;  a  power  of  spontaneous  movement  (which  finds  its  resem- 
blance in  that  of  the  sporules  of  the  Confervae,  &c.)  being  imparted 
to  them,  by  which  they  bring  themselves  into  contact  with  the  ovum. 

805.  From  this  stage,  an  entirely  new  set  of  changes  begins  to  take 
place  in  the  interior  of  the  Ovum,  during  its  passage  along  the  Fallo- 
pian tube  or  oviduct.  The  two  new  cells,  which  at  first  occupy  only 
the  pellucid  centre  of  the  germinal  spot,  rapidly  increase  in  size,  and 
begin  to  develop  new  cells  in  their  own  interior.  At  the  same  time 
they  press  upon  the  cells,  which  filled  the  germinal  vesicle  previously 
to  its  fertilization;  and  these  gradually  liquefy  or  dissolve  away,  until 
all  trace  of  them  is  lost;  and  the  twin-cells,  with  their  offspring,  are 
alone  contained  within  the  germinal  vesicle.  Each  of  the  first-formed 
cells  gives  birth,  by  the  usual  process  of  cell-development,  to  a  new 
generation  of  two  ;  so  that  the  number  is  now  four;  from  these  four 
is  produced  a  third  generation  of  eight;  and  these  go  on  progressively 
doubling,  until  at  last  a  mass  is  produced,  closely  resembling  a  mul- 
berry, in  which  the  number  of  cells  is  too  great  to  admit  of  being 
counted.     This  "  mulberry  mass"  is  obviously  analogous  to  the  col- 


GERMINAL  MEMBRANE.— CICATRICULA.  457 

lection  of  cells,  which  is  first  developed  within  the  seed  of  the  Flower- 
ing Plant  (§  783);  and  between  the  condition  of  the  Animal  and  that 
of  the  Vegetable  embryo,  at  this  period,  there  would  not  seem  to  be 
any  essential  difference. 

806.  In  the  next  stage,  however,  a  marked 

difference  shows  itself,  which  is  very  charac-  Fig.isi. 

teristic  of  the  two  kingdoms  respectively.  The 
mass  of  cells,  which  is  the  rudiment  of  the 
Vegetable  embryo,  spreads  itself  out  into  a  flat 
leaf-like  expansion, — the  primary  frond,  or  co- 
tyledon,— which  remains  as  the  permanent 
form  of  the  lowest  plants,  but  is  only  tempo- 
rary in  the  higher  (§  782).  But  in  the  embryo 
of  the  Animal,  the  ''  mulberry  mass,"  having 
moved  up  to  the  side  of  the  yelk,  and  having       Plan  of  early  uterine  ovum. 

1  n    .,  1  ■       .   ',  1       •  Within  the  external  ring,  or 

become  flattened  against  its  enveloping  mem-  zona  peiiucida,  are  the  serous 
brane,  sends  off  from  its  edges  a  layer  of  cells,  IrSpiem^e'rnb^r'yo;  c.'  "'^ 
which  passes  round  the  yelk,  so  as  completely 

to  enclose  it  within  a  membranous  envelop,  the  exterior  of  which  is  in 
contact  with  the  yelk-bag.  A  second  layer  is  afterwards  formed 
within  the  preceding,  from  the  central  part  of  the  mulberry  mass ;  and, 
in  the  higher  animals,  a  third  is  subsequently  formed  between  them. 
This  membranous  formation,  as  a  whole,  is  known  as  the  germinal 
membrane  ;  its  external  pellicle  is  termed  the  serous  layer  ;  the  internal 
is  termed  the  mucous  layer ;  and  the  intermediate  one,  which  gives 
origin  to  the  first  vessels  of  the  embryonic  structure,  is  termed  the 
vascular  layer. 

807.  Thus  the  first  development  of  the  Animal  embryo  is  into  a 
sac,  enclosing  the  store  of  nutriment  that  has  been  prepared  for  it, — 
in  fact,  a  stomach ;  and  we  shall  presently  see,  that  it  is  by  the  agency 
of  the  walls  of  this  sac,  that  the  nutrient  materials  which  it  encloses 
are  prepared  for.  being  appropriated  to  the  development  of  the  more 
permanent  part  of  the  fabric,  which  is  to  be  evolved  from  the  centre  of 
the  mulberry  mass.  But  we  may  here  stop  to  notice  the  interesting 
fact,  that  the  development  of  the  ovum  in  the  /oz^es^  classes  of  animals 
may  be  said  almost  to  stop  at  this  point ;  the  external  layer  of  the 
germinal  membrane  remaining  as  the  integument ;  the  internal  layer 
becoming  the  lining  of  the  stomach ;  and  the  space  occupied  by  the 
yelk  forming  the  digestive  cavity,  into  which  an  entrance  or  mouth  is 
formed,  by  the  thinning-away  of  the  germinal  membrane  at  a  certain 
point,  round  which  tentacula  or  prolonged  lips  are  usually  developed. 
This  is  the  essential  part  of  the  history  of  development  in  the  simpler 
Polypes ;  and  we  see  how  remarkably  it  corresponds  with  the  history 
of  development  of  the  lower  Cryptogamic  plants,  in  which  the  first- 
formed  membranous  expansion,  or  primary  frond,  remains  as  the  per- 
manent leaf. 

808.  In  the  higher  Animals,  on  the  other  hand,  the  greater  part  of 
the  germinal  membrane,  and  of  the  cavity  which  it  forms,  have  a 


458  FORMATION  OF  CHORION. 

merely  temporary  purpose ;  being  cast  off,  when  they  have  performed 
their  function,  like  the  cotyledons  of  Flowering  Plants.  Nearly  the 
whole  of  the  permanent  structure  of  the  embryo  is  formed  from  a 
single  large  cell;  which  at  first  occupies  the  centre  of  the  "mulberry 
mass ;"  but  which  is  seen  at  the  surface  of  the  latter,  when  this  under- 
goes the  flattening  already  described.  This  cell,  together  with  the 
cluster  of  ordinary  cells  that  surrounds  it,  is  that  which  forms  the 
cicatricula  or  germ-spot  upon  the  surface  of  the  yelk-bag,  in  the  im- 
pregnated ovum  of  the  Fowl;  and,  whilst  still  retaining  its  clearness, 
it  forms  a  large  round  transparent  space  in  the  centre  of  the  cicatricula, 
which  is  known  as  the  Area pellucida.  The  nucleus  of  this  Embryonic 
cell,  which  was  at  first  annular,  changes  its  form  into  that  of  a  pear, 
and  then  into  that  of  a  violin  ;  and  consists  at  last  of  two  long  parallel 
lines,  enclosing  a  narrow  space  between  them,  but  separating  and 
enclosing  a  wider  space  at  one  extremity.  In  this  state,  it  is  called 
the  Primitive  Trace.  The  same  process  then  takes  place  within  the 
Embryonic  cell,  which  has  been  described  as  occurring  within  the 
Germinal  vesicle ;  the  granules  forming  the  outer  border  of  the  nucleus 
being  first  developed  into  cells;  these  being  pushed  outwards  by  a 
new  series  subsequently  generated  nearer  the  centre;  and  these  being 
displaced,  in  their  turn,  by  a  continuance  of  the  same  process.  It  is 
from  the  peripheral  cells  originating  in  this  primitive  trace,  that  the 
inner  layers  of  the  germinal  membrane  (§  806)  seem  to  be  developed ; 
the  cells  that  originate  nearer  its  centre,  are  those  from  which  the 
more  permanent  portions  of  the  embryonic  fabric  are  evolved.  The 
principal  steps  of  that  process  will  be  presently  noticed ;  we  must  now 
stop  to  consider  the  changes  which  take  place  in  the  female  gene- 
rative apparatus,  subsequently  to  the  liberation  of  the  ovum  from  the 
ovarium,  but  having  relation  to  the  new  connection,  which  is  to  be 
afterwards  formed  between  the  embryo  and  its  parent. 

809.  During  the  time  which  is  occupied  by  these  important  changes, 
the  Ovum  passes  through  the  Fallopian  tubes,  and  makes  its  way  into 
the  Uterus.  During  its  transit  through  the  Fallopian  tubes,  the  Mam- 
malium  ovum, — like  the  ovum  of  Birds  in  its  passage  through  the  ovi- 
duct,— receives  an  additional  layer  of  albuminous  matter  secreted  from 
the  walls  of  the  tube ;  and  this  is  surrounded  by  a  fibrous  membrane, 
whose  structure  and  mode  of  formation  have  been  described  on  a  for- 
mer occasion  (§  181).  The  outer  layer  of  this  envelop,  in  the  egg  of 
the  Bird,  is  further  consolidated  by  the  deposition  of  particles  of  car- 
bonate of  lime  in  its  areolae  ;  but  it  undergoes  no  higher  organization. 
In  the  Mammal,  however,  this  new  envelop  (termed  the  Chorion)  is 
a  formation  of  great  importance  ;  being  the  medium  through  which  the 
whole  subsequent  nutrition  of  the  embryo  is  derived.  This  is  at  first 
taken  in  by  means  of  a  number  of  villous  processes,  proceeding  from 
the  entire  surface  of  the  Chorion,  and  giving  it  a  spongy  or  shaggy 
appearance  ;  these  processes  (which  are  composed  of  nucleated  cells) 
serve  as  absorbing  radicles,  which  draw  in  the  fluids  afforded  by  the 
parent ;  and  they  thus  make  up  for  the  early  exhaustion  of  the  small 


FORMATION  OF  DECIDUA,  AND  VILLI  OF  CHORION.  459 

supply  of  nutritious  matter  stored  up  in  the  ovum  itself.  The  contained 
embryo  appropriates  the  fluid  which  is  thus  imbibed,  by  simple  ab- 
sorption through  its  surface;  and  thus  it  is  nourished,  until  a  more 
special  provision  for  its  development  comes  into  action.  The  struc- 
ture of  this  organ,  termed  the  Placenta^  cannot  be  understood,  until 
the  concurrent  changes  in  the  lining  membrane  of  the  Uterus  have 
been  considered. 

810.  This  membrane,  in  its  natural  condition,  presents  on  its  free 
surface  the  orifices  of  numerous  cylindrical  follicles ;  which  are  ar- 
ranged parallel  to  each  other,  and  at  right  angles  to  the  surface.  In  the 
spaces  between  these  follicles,  the  blood-vessels  form  a  dense  capillary 
network.  When  impregnation  takes  place,  this  mucous  membrane 
swells  and  becomes  lax  ;  its  capillaries  increase  in  size ;  the  follicles 
are  turgid  with  a  white  epithelium ;  and  the  interfollicular  spaces  are 
crowded  with  nucleated  cells,  which  fill  up  the  meshes  of  the  capillary 
network.  In  this  peculiar  condition,  the  uterine  mucous  membrane 
is  termed  the  Beddua.  At  a  later  period,  the  decidua  may  be  found 
to  consist  of  two  distinct  layers ;  the  decidua  vera^  lining  the  uterus ; 
and  the  decidua  reflexa,  covering  the  exterior  of  the  ovum.  It  was 
formerly  supposed  that  the  latter  was  a  portion  of  the  former,  which 
had  been  pushed  before  the  ovum  at  its  entrance  into  the  uterus;  but 
the  two  layers  are  now  known  to  be  so  different  in  texture,  that  they 
cannot  be  supposed  to  have  the  same  origin ;  and  there  seems  much 
probability  in  Mr.  Goodsir's  view,  that  the  decidua  vera  is  chiefly 
formed  by  the  highly  vascular  mucous  membrane  itself,  and  the  deci- 
dua reflexa  by  the  abundant  production  of  epithelial  cells  from  its 
follicles. 

811.  When  the  ovum  has  arrived  in  the  Uterus,  therefore,  and  the 
villous  tufts  of  its  chorion  are  developed,  these  come  into  contact,  in 
the  first  instance,  w^ith  the  layer  of  cellular  decidua,  which  intervenes 
between  them  and  the  vascular  decidu?i.  Through  this  cellular  mem- 
brane, therefore,  the  ovum  must  derive  its  nutriment  from  the  vascular 
surface ;  and  it  cannot  be  deemed  improbable,  that  the  office  of  the 
cellular  decidua  is  to  draw  from  the  subjacent  vessels  the  materials 
which  are  to  serve  for  the  nutrition  of  the  ovum,  and  to  present  it  to 
the  villous  tufts  of  the  chorion.  Each  of  these,  as  already  mentioned, 
is  composed  of  an  assemblage  of  nucleated  cells,  which  are  found  in 
various  stages  of  development;  and  these  are  always  enclosed  within 
a  layer  of  basement-membrane,  which  seems  itself  to  be  composed  of 
flattened  cells  united  by  their  edges.  At  the  free  extremity  of  each 
villus,  is  a  bulbous  expansion,  the  cells  composing  which  are  arranged 
round  a  central  spot ;  and  it  is  at  this  point  that  the  most  active  pro- 
cesses of  growth  take  place,  the  villus  elongating  by  the  development 
of  new  cells  from  its  germinal  spot,  and,  like  the  spongiole  of  the 
plant,  drawing  in  nutriment  from  the  soil  in  which  it  is  imbedded. — 
In  its  earliest  grade  of  development,  as  already  remarked,  the  chorion 
and  its  villi  contain  no  vessels ;  and  the  fluid  drawn  in  by  the  tufts  is 
communicated  to  the  embryo,  by  the  absorbing  powers  of  its  germinal 


460       FORMATION  OF  VERTEBRAL  COLUMN,  AND  OF  VESSELS. 


membrane.  But  when  the  tufts  are  penetrated  by  blood-vessels,  and 
their  communication  with  the  embryo  becomes  much  more  direct,  the 
means  by  which  they  communicate  with  the  parent  are  found  to  be 
essentially  the  same  ; — namely,  a  double  layer  of  cells,  one  layer 
belonging  to  the  foetal  tuft,  the  other  to  the  vascular  maternal  surface. 
(See  §  819.) 

812.  We  now  return  to  the  Embryo  itself;  the  general  history  of 
whose  development  has  been  already  traced,  up  to  the  period  at  which 
the  inner  part  of  the  elongated  nucleus  of  the  embryonic  cell  is  begin- 
ning to  give  origin  to  the  permanent  structures  of  the  foetus.  The 
parts  first  formed  in  the  embryo  of  Vertebrated  animals,  are  such  as 
most  characteristically  distinguish  them  from  all  others ; — namely,  the 
Vertebral  column,  and  Spinal  Cord.  The  latter  is  formed  in  the 
groove,  which  runs  along  the  median  line  of  the  primitive  trace ;  and 
it  is  surrounded,  when  first  developed,  by  a  tubular  structure,  which 
has  but  a  temporary  existence  in  the  higher  Vertebrata,  but  which  is 
permanent  in  the  lower  Fishes.  This  structure,  termed  the  Chorda 
dorsalis,  is  found  to  be  composed,  wherever  it  exists,  of  nucleated 
cells.  From  the  cells  exterior  to  this,  the  vertebral  column  is  deve- 
loped ;  and  this  makes  its  first  appearance  in  the  condition  of  two 
rows  of  minute  opaque  plates,  imbedded  in  ridges  that  rise  up  on 
either  side  of  the  central  groove,  and  constituting  the  arches  of  the 
incipient  vertebrae.  These  ridges  incline  towards  each  other;  and  at 
last  meet  and  cover-in  the  groove,  so  as  to  complete  the  bony  cylinder 
protecting  the  spinal  cord.  Towards  the  anterior  extremity,  how- 
ever, they  do  not  at  once  close  in ;  and  the  large  cells,  in  which  the 
great  divisions  of  the  Encephalon  originate,  may  be  seen  between 
them. 

813.  During  the  progress  of 
this  change,  another  very  im- 
portant one  is  taking  place,  which 
has  reference  to  the  nutrition  of 
the  embryo  during  its  further  de- 
velopment. This  is  the  formation 
of  vessels  in  the  substance  of  the 
germinal  membrane ;  which  ves- 
sels serve  to  take  up  the  nourish- 
ment supplied  by  the  yelk,  as 
well  as  that  derived  from  the 
chorion  externally,  and  to  con- 
vey it  through  the  tissues  of  the 
embryo.  These  vessels  are  first 
seen  in  that  part  of  the  vascular 
lamina  of  the  germinal  mem- 
brane, which  immediately  sur- 
rounds the  embryo ;  and  they 
form  a  network,  bounded  by  a 
circular  channel,  which  is  known 


Fig.  132. 


Vascular  Area  of  Fowl's  egg,  at  the  beginning  of 
the  third  day  of  incubation ;— a,  a,  yelk;  6,  b,  6,  b, 
venous  sinus  bounding  the  area:  c,  aorta;  d,  punc- 
tum  saliens,  or  incipient  heart;  e,  e,  area  pellucida; 
/,/,  arteries  of  the  vascular  area;  §■,§•,  veins;  A,  eye. 


FORMATION  OF  VESSELS  AND  DIGESTIVE  CAVITY.  461 

under  the  name  of  the  Vascular  Area  (Fig.  132).  This  gradually 
extends  itself,  until  the  vessels  spread  over  the  whole  of  the  germinal 
membrane.  The  vessels  are  probably  formed  by  the  coalescence  of 
the  original  cells  of  the  layer;  and  the  first  blood-discs  which  they 
contain  seem  to  originate  in  the  nuclei  of  these  cells.  This  network 
of  vessels  serves  to  receive  the  nutritious  matter  contained  in  the 
yelk-bag,  and  to  convey  it  to  the  embryo ;  but  the  act  of  absorption 
seems  to  be  performed  here  as  elsewhere,  by  cells, — a  layer  of  which 
always  intervenes  between  the  vascular  layer  and  the  yelk  itself. 
These  cells  probably  correspond  in  function  with  those  of  the  villi  of 
the  intestinal  canal  in  the  adult  (§  242);  as  the  vessels  of  the  yelk- 
bag,  or  temporary  digestive  cavity,  represent  those  of  the  alimentary 
canal,  to  be  afterwards  developed  from  a  portion  of  it.  The  vessels 
of  the  yelk-bag  terminate  in  two  large  trunks,  which  enter  the  embryo 
at  the  point  that  afterwards  becomes  the  umbilicus,  and  which  are 
known  as  the  Omphalo- Mesenteric^  Meseraic,  or  Vitelline  vessels.  The 
first  movement  of  fluid  takes  place  towards  the  embryo ;  and  this  may 
be  witnessed  before  any  distinct  heart  is  evolved. 

814.  The  formation  of  the  Heart  takes  place  in  the  substance  of 
the  Vascular  layer ;  by  a  dilatation  of  the  trunk,  into  which  the  blood- 
vessels unite.  At  first  it  appears  as  a  mere  excavation,  surrounded 
by  cells ;  but  its  walls  gradually  acquire  firmness  and  consistency, 
and  are  endowed  with  a  contractile  power  that  enables  them  to  exe- 
cute regular  pulsations.  In  this  early  condition,  the  heart  is  known 
as  the  punctum  saliens  {d,  Fig.  132).  The  first  appearance  of  the 
heart  in  the  Chick  is  at  about  the  27th  hour;  the  time  of  its  forma- 
tion in  Mammalia  has  not  been  distinctly  ascertained. 

815.  Concurrently  with  the  formation  of  the  Vascular  system,  the 
production  of  the  permanent  Digestive  cavity  commences.  This 
originates  in  the  separation  of  a  small  portion  of  the  yelk-bag,  lying 
immediately  beneath  the  embryo,  from  the  general  cavity,  in  the  fol- 
lowing manner. — At  about  the  25th  hour  of  incubation,  in  the  Fowl's 
egg,  the  parts  of  the  germinal  membrane  which  lie  beyond  the  extre- 
mities, and  which  spread  out  from  the  sides  of  the  embryo,  are  doubled 
in,  so  as  to  make  a  depression  upon  the  yelk ;  and  their  folded  edges 
gradually  approach  one  another  under  the  abdominal  surface  of  the 
embryo,  so  as  at  last  to  meet  and  enclose  a  cavity,  which  is  at  first 
simple  in  its  form,  but  which  is  subsequently  rendered  more  complex 
by  the  prolongation  and  involution  of  its  walls  in  various  parts,  so  as 
to  form  the  stomach  and  intestinal  tube  (Figs.  133,  134,  135).  This 
digestive  cavity  communicates  for  some  time  with  the  yelk-bag  (from 
which  it  has  been  thus  pinched  off,  as  it  were),  by  a  wide  opening, 
that  is  left  by  the  imperfect  meeting  of  the  folds  of  the  germinal 
membrane  that  constitute  its  walls.  In  the  Mammalia,  this  orifice  is 
gradually  narrowed,  and  is  at  last  completely  closed  ;  and  the  yelk- 
bag,  thus  separated,  is  afterwards  thrown  off.  It  may  be  detected, 
however,  upon  the  umbilical  cord,  up  to  a  late  period  of  pregnancy, 
and  is  known  as  the  Umbilical  vesicle.     In  Birds,  and  other  oviparous 


462 


FORMATION  OF  DIGESTIVE  CAVITY  AND  AMNION. 


animals,  the  whole  of  the  yelk-bag  is  ultimately  drawn  into  the  abdo- 
men of  the  embryo  ;  the  former  gradually  shrinking,  as  its  contents 
are  exhausted  ;  and  the  latter  enlarging,  so  as  to  receive  it  as  a  little 
pouch  or  appendage.  In  Fishes,  the  hatching  of  the  egg  very  com- 
monly takes  place  before  the  process  has  been  completed  ;  so  that 
the  little  Fish  swims  about  with  the  yelk-bag  hanging  from  its  body. 
816.  Whilst  these  processes  are  going  on  in  the  Vascular  and  Mu- 
cous layers  of  the  Germinal  membrane,  a  remarkable  change  is  taking 
place  in  that  portion  of  the  Serous  lamina,  which  surrounds  the  Area 
pellucida.     This  rises  up  on  either  side  in-^two  folds  (Fig.  133) ;  and 


Fig.  133. 


Fig.  134. 


Diagram  of  ovum  at  later  stage  ;  the  digestive 
cavity  beginning  to  be  separated  from  the  yelk- 
sac,  and  the  amnion  beginning  to  be  formed:— a, 
chorion;  b,  yelk-sac ;  c,  embryo;  d  and  e,  folds 
of  the  serous  layer  rising  up  to  form  the  Amnion. 


The  Amnion  in  process  of  formation,  by  the 
arching  over  of  the  serous  lamina :— a,  the  cho- 
rion; &,  the  yelk-bag,  surrounded  by  serous  and 
vascular  laminaj;  c,  the  embryo;  d,  e,  and/,  ex- 
ternal and  internal  folds  of  the  serous  layer,  form- 
ing the  amnion ;  g,  incipient  allantois. 


these  gradually  approach  one  another,  at  last  meeting  in  the  space  be- 
tween the  general  envelop  and  the  embryo,  so  as  to  form  an  addi- 
tional investment  to  the  latter.  As  each  fold  contains  two  layers  of 
membrane,  a  double  envelop  is  thus  formed  ;  of  which  the  outer  layer 
(Fig.  134,  d,  e,  and  Fig.  135,  A),  afterwards  adheres  to  the  inner  sur- 
face of  the  chorion, — the  original  yelk-bag,  or  Zona  pellucida,  being 
now  lost  sight  of;  whilst  the  inner  one  (Fig.  134,y*,y*,  and  Fig.  135, 
jT),  remains  as  a  distinct  sac,  to  which  the  name  of  Amnion  is  given. 
This  takes  place  during  the  third  day  in  the  Chick  ;  but  the  period  at 
which  it  occurs  in  the  Human  Ovum  has  not  yet  been  clearly  ascer- 
tained. 

817.  The  embryo,  like  the  adult,  has  need  of  Respiration  ;  in  or- 
der that  the  carbonic  acid  set  free  in  the  Nutritive  operations  may 
be  removed  from  its  fluids.  In  Fishes,  the  surrounding  water  acts 
with  sufficient  powder  upon  the  vessels  of  the  yolk-bag,  to  produce  the 
required  aeration,  up  to  the  time  when  the  gills  of  the  young  animal 
are  ready  to  come  into  play.  But  in  the  higher  oviparous  animals, 
whose  development  proceeds  further  before  they  leave  the  egg,  a 
more  special  provision  is  made  for  the  purpose.  A  bag,  termed  the 
allantois,  sprouts  (as  it  were)  from  the  lower  end  of  the  intestine  (Fig. 


RESPIRATION  OF  EMBRYO  ;—ALLANTOIS. 


463 


Fig.  135 


134,^);  and  gradually  enlarges,  passing  round  the  embryo  (Fig 
135,  g),  so  as  in  Birds  almost  com- 
pletely to  enclose  it,  intervening  be- 
tween the  germinal  membrane  and 
the  shell,  and  receiving  the  direct 
influence  of  the  air  that  penetrates 
the  latter.  It  is  thus  the  temporary 
lung  of  the  air-breathing  oviparous 
animal ;  and  it  serves  for  the  aera- 
tion of  its  fluids,  up  to  the  time 
when  it  quits  the  egg.  In  the  Ovum 
of  the  Mammal,  the  chief  office  of 
the  Allantois  is  to  convey  the  ves- 
sels of  the  Embryo  to  the  Chorion ; 
and  its  extent  bears  a  pretty  close 
correspondence  with  the  extent  of 
surface,  through  which  the  Chorion 
comes  into  vascular  connection  with 


the  Decidua, — this    extent  varying 


Diagram  representing  a  Human  Ovura  in 
second  month  : — a,  1,  smooth  portion  of  cho- 
rion; a,  2,  villous  portion  of  chorion;  k,  k, 
elongated  villi,  beginning  to  collect  into  Pla- 
centa; 6,  yolk-sac  or  umbilical  vesicle;  c,  em- 
bryo ;  /,  amnion  (inner  layer);  §■,  allantois; 
/i,  outer  layer  of  amnion,  coalescing  with 
chorion. 


considerably  in  the  different  orders 
of  Mammalia.  Thus  in  the  Car- 
nivora,  whose  placenta  extends  like  a  band  around  the  whole  ovum, 
the  allantois  also  lines  the  whole  inner  surface  of  the  chorion,  except 
where  the  umbilical  vesicle  comes  into  contact  with  it.  On  the  other 
hand,  in  Man  and  the  Quadrumana,  whose  placenta  is  restricted  to 
one  spot,  the  allantois  is  small,  and  conveys  the  foetal  vessels  to  one 
portion  only  of  the  Chorion.  When  these  vessels  have  reached  the 
Chorion,  they  ramify  in  its  substance,  and  send  filaments  into  its 
villi ;  and  in  proportion  as  these  villi  form  that  connection  with  the 
uterine  structure  which  has  been  already  described  (§  811),  do  the 
vessels  increase  in  size.  They  then  pass  directly  from  the  fcetus  to 
the  chorion ;  and  the  allantois,  being  no  longer  of  any  use,  shrivels 
up  like  the  Yelk-bag,  and  remains  as  a  minute  vesicle,  only  to  be 
detected  by  careful  examination.  The  lower  part  of  it,  however, 
pinched  off  (as  it  w^ere)  from  the  rest,  remains  as  the  Urinary  blad- 
der; and  the  Urachus  or  suspensory  ligament  of  the  latter  represents 
the  duct,  by  which  the  Allantois  was  originally  connected  with  the 
abdominal  cavity. 

818.  The  connection  which  is  thus  formed  between  the  Vascular 
system  of  the  fcetus  and  that  of  the  parent,  is  the  only  one  that  exists 
in  the  lower  Mammalia  ;  which  are  thus  properly  designated  as  '*  non- 
placental."  Each  villus  of  the  Chorion  contains  a  capillary  loop  ;  this 
is  enclosed  in  a  layer  of  cells;  and  this  again  in  a  lamina  of  base- 
ment-membrane ; — the  whole  forming  the  fcetal  tuft.  This  comes 
into  contact  with  the  cellular  decidua,  which  lies  upon  the  basement- 
membrane  covering  the  vascular  layer  of  the  decidua.  Now  the 
Placenta  is  composed  of  these  very  elements,  arranged  in  a  more 
complex  manner.     It  is  formed  by  an  extension  of  the  vascular  tufts 


464 


STRUCTURE  OF  THE  PLACENTA. 


of  the  chorion  at  certain  parts ;  and  a  corresponding  adaptation,  on 
the  part  of  the  Uterine  structure,  to  afford  to  these  an  increased 
supply  of  nutritious  fluid.  These  specially  prolonged  portions  are 
scattered,  in  the  Ruminants  and  some  other  Mammalia,  over  the 
whole  surface  of  the  Chorion,  forming  what  are  termed  the  Cotyle- 
dons; but  in  the  higher  orders,  and  in  Man,  they  are  concentrated 
in  one  spot,  forming  the  Placenta.  In  some  of  the  lower  tribes,  the 
maternal  and  foetal  portions  of  the  placenta  may  be  very  easily  sepa- 
rated ;  the  former  consisting  of  the  thickened  decidua ;  and  the  latter 
being  composed  of  the  prolonged  and  ramifying  vascular  tufts  of  the 
Chorion,  which  dip  down  into  it.  But  in  the  Human  placenta,  the 
two  elements  are  mingled  together  through  its  whole  substance. 

819.  The  Foetal  portion  of  the  placenta  consists  of  the  branches  of 
the  umbilical  vessels;  which  subdivide  at  the  point  at  which  they 
enter  the  mass,  and  form,  by  their  minute  ramifications,  a  large  part 
of  its  substance.  Each  villus  contains  a  capillary  vessel,  which 
forms  a  series  of  loops,  communicating  with  an  artery  on  the  one 
side,  and  with  a  vein  on  the  other;  but  the  same  capillary  may  enter 
several  villi,  before  re-entering  a  larger  vessel.  The  vessels  of  the 
villi  (Fig.  136,  g)  are  covered,  as  in  the  chorion,  by  a  layer  of  cells, 
(y*,)  enclosed   in  basement-membrane  (e) ;    but  the   foetal  tuft   thus 


Fig.  136. 


Fig.  137. 


Extremity  of  a  placental  villus:— a,  external  Portion  of  the  external  membrane,  with  the 

membrane  of  the  villus,  continuous  witii   the  external  cells,  of  a  placental  villus: — a,  cells 

lining  membrane  of  the  vascular  system  of  the  seen  through  the  membrane  ;  6,  cells  seen  from 

mother;  b,  external  cells  of  the  villus,  belonging  v^^ithin  the  villus;  e,  cells  seen  in  profile  along 

to  the  placental  decidua;  c,  c,  germinal  centres  the  edge  of  the  villus, 

of  the  external  cells;  d.  the  space  between  the 
maternal  and  foetal  portions  of  the  villus;  e,  the 
internal  membrane  of  the  villus,  continuous  with 
the  external  membrane  of  the  chorion;/,  the  in- 
ternal cells  of  the  villus,  belonging  to  the  cho- 
rion; g,  the  loop  of  umbilical  vessels. 

formed  is  enclosed  in  a  second  series  of  envelops  (a,  6,  c),  derived 
from  the  maternal  portion  of  the  placenta, — a  space  (d)  being  left 
between  the  two,  however,  at  the  extremity  of  the  tuft.  The  vas- 
cular tufts  not  unfrequently  extend  beyond  the  uterine  surface  of  the 
placenta,  and  dip  down  into  the  uterine  sinuses,  where  they  are 
bathed  in  the  maternal  blood.  The  Maternal  portion  of  the  Placenta 
may  be  regarded  as  a  large  sac,  formed  by  a  prolongation  of  the 
internal  coat  of  the  great  Uterine  vessels.  Against  the  foetal  surface 
of  this  sac,  the  tufts  just  described  may  be  said  to  push  themselves, 


STRUCTURE  OF  THE  PLACENTA. 


465 


Fig.  138. 


Diagram  ilJustrating  the  arrangement  of  the  pla- 
cental decidua:  —  a,  decidua  in  contact  with  the 
interior  of  the  uterus;  6,  venous  sinus  passing  ob- 
liquely through  it  by  a  valvular  opening;  c,  a  curling 
artery  passing  in  the  same  direction;  rf,  the  lining 
membrane  of  the  maternal  vascular  system,  passing 
in  from  the  artery  and  vein  lining  the  bag  of  the  pla- 
centa, and  covering  e,  e,  the  foetal  tufts,  passing  on  to 
them  from  their  stems  from  the  foetal  side  of  the 
cavity,  also  by  the  terminal  decidual  bars/,/,  from 
the  uterine  side,  and  from  one  tuft  to  the  other  by  the 
lateral  bar,  g;  h,h,  separated  foBtal  tufts,  showing  the 
internal  membrane  and  cells,  which,  with  the  loops- 
of  umbilical  vessels,  constitute  the  true  foelal  portion 
of  the  tufts. 


SO  as  to  dip  down  into  it,  carrying  before  them  a  portion  of  its  thin 
wall,  which  constitutes  a  sheath  to  each  tuft.  In  this  manner,  the 
whole  interior  of  the  placental 
cavity  is  intersected  by  nume- 
rous tufts  of  foetal  vessels,  dis- 
posed in  fringes,  and  bound 
down  by  the  membrane  that 
forms  its  proper  wall, — ^just  as 
the  intestines  are  covered  and 
held  in  their  places  by  the 
peritoneum.  Now  as  this  di- 
latation of  the  uterine  blood- 
vessels carries  the  decidua 
before  it,  every  one  of  the 
vascular  tufts  that  dips  down 
into  it  will  be  covered  with  a 
layer  of  the  cellular  structure 
of  the  latter  (Fig.  137,  and 
Fig.  138,  e) ;  and  this  will  also 
form  a  part  of  all  the  bands 
that  connect  and  tie  down  the 
tufts  (Fig.  138,^).  The  blood 
is  conveyed  into  the  cavity  of 
the  placenta  by  the  '^  curling 
arteries,"  so  named  from  their 

peculiar  course  (Fig.  138,  c),  which  proceed  from  the  arteries  of  the 
uterus ;  and  it  is  returned  by  large  short  straight  trunks,  which  pass 
obliquely  through  the  decidua  (Fig.  138,  6),  and  discharge  their  con- 
tents into  the  great  uterine  sinuses. 

820.  There  is  no  more  direct  communication  between  the  Mother 
and  Foetus  than  this ;  all  the  observations,  which  have  been  supposed 
to  prove  a  direct  vascular  continuity,  being  certainly  fallacious.  The 
function  of  the  Placenta  is  manifestly  double.  The  foetal  tufts  draw, 
from  the  maternal  blood,  the  materials  w^hich  are  required  for  the 
nutrition  of  the  embryo, — these  materials  having  been  first  selected 
and  partially  elaborated  by  the  two  sets  of  intervening  cells :  and  in 
this  character,  the  foetal  tufts  resemble  the  villi  of  the  intestinal  sur- 
face, which  dip  down  into  the  fluids  of  the  alimentary  canal,  and 
absorb  the  nutritive  material  which  they  furnish.  But  the  Placenta 
also  serves  as  a  respiratory  organ  ;  aerating  the  blood  of  the  foetus, 
by  exposing  it  to  the  influence  of  the  oxygenated  blood  of  the  Mother : 
and  in  this  respect  the  foetal  tufts  bear  a  close  correspondence  with 
the  gills  of  aquatic  animals,  bringing  the  blood  into  relation  with  a 
surrounding  fluid  medium  containing  oxygen,  which  is  imbibed  by 
the  blood  in  exchange  for  the  carbonic  acid  given  ofl". 

821.  The  formation  of  the  Human  Placenta  commences  in  the  latter 
part  of  the  second  month  of  utero-gestation ;  during  the  third,  it  ac- 
quires its  proper  character;  and  it  subsequently  goes  on  increasing,  in 

30  :  "!  vii.. 


466 


CIRCULATION  IN  FCETUS. 


Fig.  139. 


o   o 


K)  V 


The  fcEtal  circulation  1.  The  umbilical  cord, 
consisting  of  ihe  umbilical  vein  and  two  umbilical 
arteries :  proceeding  from  the  placenta  (2).  3.  The 
umbilical  vein  dividing  into  three  branches;  two 
(4.  4)  to  be  distributed  to  the  liver;  and  one  (5),  the 
ductus  venosus,  vv^hich  enters  the  inferior  vena 
cava  (6).  7  The  portal  vein,  returning  the  blood 
from  the  intestines,  and  uniting  with  the  right 
hepatic  branch.  8.  The  right  auricle  ;  the  course 
of  the  blood  is  denoted  by  the  arrow,  proceeding 
from  8  to  9,  the  left  auricle.  10.  The  left  ventricle  ; 
the  blood  following  the  arrow  to  the  arch  of  the 
aorta  (11).  to  be  distributed  through  the  branches 
given  off  by  the  arch  to  the  head  and  upper  ex- 
tremities. The  arrows  12  and  13.  represent  the 
return  of  the  blood  from  the  head  and  upper  extre- 
mities through  the  jugular  and  subclavian  veins, 
to  the  superior  vena  cava  (14),  to  the  right  auricle 
(8).  and  in  the  course  of  the  arrow  through  the 
right  ventricle  (15),  to  the  pulmonary  artery  (16). 
17.  The  ductus  arteriosus,  which  appears  lo  be  a 
proper  continuation  of  the  pulmonary  artery  ;  the 
offsets  at  each  side  are  the  right  and  left  pulmo- 
nary artery  cut  off;  these  are  of  extremely  small 
size  as  compared  with  the  ductus  arteriosus.  The 
ductus  arteriosus  joins  the  descending  aorta  (18, 
18).  which  divides  into  the  common  iliacs,  and 
these  into  the  internal  iliacs,  which  become  the 
hypogastric  arteries  (19),  and  return  the  blood 
along  the  umbilical  cord  to  the  placenta;  while 
the  other  divisions,  the  external  iliacs  (20),  are 
continued  into  the  lower  extremities.  The  arrows 
at  the  terminations  of  these  vessels  mark  the  re- 
turn of  the  venous  blood  by  the  veins  to  the  inferior 
cava. 


accordance  with  the  growth  of  the 
ovum.  The  vessels  of  the  Ute- 
rus undergo  great  enlargement 
throughout;  but  especially  at  the 
part  to  which  the  Placenta  is  at- 
tached ;  and  the  blood,  in  moving 
through  them,  produces  a  peculiar 
murmur,  which  is  usually  audible 
with  distinctness  at  an  early  period 
of  pregnancy,  and  which  may  be 
regarded  (when  due  care  is  taken 
to  avoid  sources  of  fallacy)  as  one 
of  its  most  unequivocal  physical 
signs.  The  sound  is  most  com- 
monly heard  near  the  situation  of 
the  Fallopian  tube  of  the  right 
side ;  and  it  corresponds  with  the 
pulse  of  the  mother. 

822.  It  would  be  inconsistent 
with  the  character  and  objects  of 
this  Treatise,  to  follow,  in  any 
detail,  the  history  of  the  develop- 
ment of  the  Foetus,  during  its 
intra-uterine  life ;  and  a  general 
account  of  the  evolution  of  most 
of  the  chief  organs,  is  given  in 
connection  with  that  of  their  struc- 
ture. The  condition  of  the  Cir- 
culating apparatus,  however,  at 
the  period  of  birth,  deserves  espe- 
cial notice.  A  general  account  of 
the  development  of  the  simple 
pulsating  trunk,  which  constitutes 
its  first  form,  into  the  four-cavitied 
heart  of  the  higher  Vertebrata, — 
and  of  the  conversion  of  the  single 
trunk  proceeding  from  it,  with  its 
four  pairs  of  branchial  arches, 
into  the  aorta  and  pulmonary  arte- 
ries, with  their  chief  subdivisions, 
has  been  already  given  (§  ^^6). 
Up  to  the  time  of  birth,  however, 
the  partition  between  the  Auricles 
is  incomplete  ;  a  large  aperture, 
the  foramen  ovale^  existing  in  it. 
There  is  also  a  direct  communi- 
cation between  the  pulmonary 
artery  and  the  aorta,  by  the  ductus 
arteriosus;    and    another    direct 


F(ETAL  CIRCULATION.  467 

channel  between  the  umbilical  vein  and  the  vena  cava,  by  the  ductus 
venosus. 

823.  The  following  is  the  course  of  the  Circulation  of  the  Blood  in 
the  Foetus.  The  fluid  brought  from  the  placenta  by  the  umbilical 
vein  (Fig.  139,  3),  is  partly  conveyed  at  once  to  the  vena  cava  as- 
cendens,  by  means  of  the  ductus  venosus  (5),  and  partly  flows  through 
two  trunks  (4,  4),  that  unite  with  the  portal  vein  (7),  returning  the 
blood  from  the  intestines,  into  the  substance  of  the  liver,  thence  to  be 
returned  to  the  vena  cava  by  the  hepatic  vein.  Having  thus  been 
ti*ansmitted  through  the  two  great  depurating  organs,  the  placenta  and 
the  liver,  the  blood  that  enters  the  vena  cava  is  purely  arterial  in  its 
character ;  but  being  mixed  in  the  vessels  with  the  venous  blood  that 
is  returned  from  the  trunk  and  lower  extremities,  it  loses  this  character 
in  some  degree,  by  the  time  that  it  reaches  the  heart.  In  the  right 
auricle,  which  it  then  enters,  it  would  also  be  mixed  with  the  venous 
blood  which  is  brought  down  from  the  head  and  upper  extremities  by 
the  descending  cava  ;  were  it  not  that  a  very  curious  provision  exists^ 
to  impede  (if  it  does  not  entirely  prevent)  any  further  admixture. 
This  consists  in  the  arrangement  of  the  Eustachian  valve;  which 
directs  the  arterial  current  (that  flows  upwards  through  the  ascending 
cava)  into  the  left  side  of  the  heart,  through  the  foramen  ovale  : 
whilst  it  directs  the  venous  current  (that  is  being  returned  by  the 
descending  cava)  into  the  right  ventricle.  When  the  ventricles  con- 
tract, the  arterial  blood  contained  in  the  left  is  propelled  into  the 
ascending  Aorta,  and  supplies  the  branches  that  proceed  to  the  head 
and  upper  extremities,  before  it  undergoes  any  further  admixture : 
whilst  the  venous  blood  contained  in  the  right  ventricle,  is  forced 
into  the  Pulmonary  artery,  and  thence  through  the  ductus  arteriosus 
(17)  which  is  like  a  continuation  of  its  trunk,  into  the  descending 
aorta,  mingling  with  the  arterial  current  which  that  vessel  previously 
conveyed,  and  thus  supplying  the  trunk  and  lower  extremities  with  a 
mixed  fluid.  A  portion  of  this  is  conveyed,  by  the  umbilical  arteries, 
to  the  Placenta;  in  which  it  undergoes  the  renovating  influence  of 
the  maternal  blood  ;  and  from  which  it  is  returned  in  a  state  of  purity. 

824.  Hence  the  head  and  superior  extremities,  whose  development 
is  required  to  be  in  advance  of  that  of  the  lower,  are  supplied  with 
blood  nearly  as  pure  as  that  which  returns  from  the  placenta  ;  whilst 
the  rest  of  the  body  receives  a  mixture  of  this,  with  what  has  pre- 
viously circulated  through  the  system.  The  Pulmonary  arteries  con« 
vey  little  or  no  blood  through  the  lungs ;  the  current  of  blood,  pro- 
per H  from  the  right  ventricle,  passes  directly  onwards  through  the 
ductus  arteriosus,  into  the  aorta. — At  birth,  however,  the  course  of 
the  circulation  undergoes  great  changes,  that  it  may  be  adapted  to 
the  new  mode,  in  which  the  infant  is  henceforth  to  obtain  its  nutrition 
and  to  carry  on  its  respiration.  As  soon  as  the  lungs  are  distended 
by  the  first  inspiration,  a  portion  of  the  blood  of  the  pulmonary  artery 
is  diverted  into  them,  and  there  undergoes  aeration  ;  and,  as  this  pro- 
portion increases,  with  the  full  actiyity  of  the  lungs,  the  ductus  arte- 


468  LENGTH  OF  GESTATION. 

riosus  gradually  shrinks,  and  its  cavity  finally  becomes  obliterated. 
At  the  same  time,  the  foramen  ovale  is  closed  by  a  valvular  fold  ;  and 
thus  the  direct  communication  between  the  two  auricles  is  cut  off. 
When  these  changes  have  been  accomplished,  the  circulation  which 
was  before  carried  on  upon  the  plan  of  that  of  the  higher  Reptiles 
(§  563)  becomes  that  of  the  complete  warm-blooded  animal ;  all  the 
blood  which  has  been  returned  in  a  venous  state  to  the  right  side  of 
the  heart,  being  transmitted  through  the  lungs,  before  it  can  reach 
the  left  side,  or  be  propelled  from  its  arterial  trunks. — It  is  by  no 
means  unfrequent,  however,  for  some  arrest  of  development  to  pre- 
vent the  completion  of  these  changes ;  and  various  malformations, 
involving  an  imperfect  discharge  of  the  circulating  and  respiratory 
functions,  may  hence  result. 

825.  The  average  length  of  time,  which  elapses  between  Concep- 
tion and  Parturition,  in  the  Human  female,  appears  to  be  280  days, 
or  40  weeks.  There  can  be  little  doubt,  however,  that  Gestation 
may  be  occasionally  prolonged  for  one,  two,  or  even  three  weeks, 
beyond  that  period ;  such  prolongation  not  being  at  all  unfrequent 
amongst  the  lower  animals  ;  and  numerous  well-authenticated  in- 
stances of  it,  in  the  Human  female,  being  upon  record.  Upon  what 
circumstances  this  departure  from  the  usual  rule  is  dependent,  has 
not  yet  been  ascertained  ;  but  it  is  a  remarkable  circumstance,  ascer- 
tained by  the  observations  of  cattle-breeders,  that  the  male  has  an 
influence  upon  the  length  of  gestation, — a  large  proportion  of  cows 
in  calf  by  certain  bulls  exceeding  the  usual  period,  and  a  small  pro- 
portion falling  short  of  it.  Hence  we  must  attribute  the  prolongation 
of  the  period  to  some  peculiarity  in  the  embryo,  derived  from  its  male 
parent. 

826.  The  shortest  period  at  which  Gestation  may  terminate,  con- 
sistently with  the  life  of  the  child,  has  not  been  precisely  ascertained  ; 
the  difficulty  of  determining  the  precise  date  of  conception  being 
•usually  such,  in  this  case  as  in  the  preceding,  as  to  prevent  the  exact 
length  of  the  Gestation  from  being  known.  Thus,  the  commence- 
ment of  pregnancy  being  fixed  by  the  time  of  the  cessation  of  the 
Catamenia,  when  there  is  no  more  definite  guide,  it  is  obvious  that 
the  act  of  Conception  may  have  taken  place  during  any  part  of  the 
interval  that  has  elapsed  since  the  last  monthly  period  ;  and  thus  a 
doubt  may  exist  as  to  the  length  of  the  Gestation,  to  the  extent  of 
from  one  to  three  weeks.  There  are  very  satisfactory  cases  on  record, 
in  which,  from  the  degree  of  development  of  the  infant  at  birth,  as 
well  as  from  other  circumstances,  it  might  be  certainly  known  not 
to  have  attained  26  or  27  weeks,  or  little  more  than  six  months ; 
and  in  which,  by  careful  treatment,  the  infant  was  reared  in  a  con- 
dition of  health  and  vigour.  And  there  is  reason  to  believe,  that 
infants  have  lived  for  some  time,  and  might  probably  have  been 
reared  under  better  management,  that  were  born  as  early  as  the  24th 
or  25th  week. 

827.  The  act  of  Parturition,  by  which  the  foetus  is  expelled  from 


I 


ACT  OF  PARTURITION.  469 

the  Uterus,  is  accomplished  in  part  by  the  contractile  power  of  the 
Uterus  itself;  and  in  part  by  the  combined  operation  of  the  various 
muscles,  which  press  upon  the  abdominal  cavity,  and  which  effect 
the  expulsion  of  the  feces  and  urine.  No  account  can  be  given  of 
the  reasons,  why  this  change  should  take  place  at  the  period,  which 
has  been  mentioned  as  its  usual  date  ;  but  we  are  as  much  in  the 
dark  in  regard  to  other  periodic  phenomena  of  Animal  life.  For 
some  days  previously  to  the  commencement  of  labour,  there  is  usually 
a  slow  contraction  of  the  fibres  of  the  fundus  and  body  of  the  uterus ; 
and  a  yielding  of  those  of  the  cervix ;  so  that  the  child  lies  lower, 
and  the  size  of  the  abdomen  diminishes.  This  slow  contraction  is 
probably  not  dependent  upon  any  act  of  the  nervous  system  ;  but 
upon  the  direct  excitement  of  the  contractility  of  the  muscular  sub- 
stance of  the  uterus.  When  labour  properly  commences,  however, 
the  Spinal  system  of  nerves  comes  into  play,  and  the  uterine  contrac- 
tions are  of  a  reflex  nature.  As  before,  however,  the  act  of  contrac- 
tion is  confined  to  the  fundus  and  body  of  the  uterus  ;  the  fibres  of  the 
cervix  uteri,  and  of  the  vagina,  being  in  a  state  of  relaxation,  which 
allows  them  to  yield  to  the  pressure  of  the  child's  head.  In  the  first 
stage  of  labour,  the  Uterine  contractions  appear  to  be  alone  concerned  ; 
and  it  is  not  until  the  head  of  the  child  is  passing  through  the  os  uteri, 
and  is  entering  the  vagina,  that  the  assistance  of  the  abdominal  mus- 
cles is  called  in.  These  act,  in  the  first  instance,  as  in  ordinary 
expiration  ;  but  their  power  is  much  increased  by  the  voluntary  reten- 
tion of  the  breath,  so  that  the  whole  of  their  contractile  force  may  be 
applied  to  the  expulsion  of  the  foetus.  In  a  latter  stage  of  labour,  this 
retention  of  the  breath  becomes  involuntary,  during  the  accession  of 
the  "  pains ;"  and  the  expulsion  of  the  foetus  is  commonly  effected 
with  considerable  force,  especially  if  the  previous  resistance  has  been 
considerable. 

828.  The  same  action  which  expels  the  foetus,  usually  detaches  the 
placenta;  and  if  the  uterus  contract  with  suflScient  force,  after  this  has 
been  thrown  off,  the  orifices  of  the  vessels  which  communicated  with 
it  are  so  effectually  closed,  that  little  or  no  hemorrhage  from  that 
source  takes  place.  When  efficient  contractions  do  not  occur,  they 
may  frequently  be  excited  by  pressure  upon  the  uterus  itself;  by  the 
application  of  cold  to  the  abdominal  surface,  to  the  extremities,  and 
(in  severe  hemorrhage)  to  the  entire  body:  or  by  the  application  of  the 
child  to  the  nipple,  which  will  frequently  at  once  succeed  in  producing 
the  desired  effect.  The  efficacy  of  these  means, — the  latter  in  parti- 
cular,— obviously  depends  upon  the  influence  of  the  spinal  system  of 
nerves  upon  the  muscular  fibres  of  the  uterus ;  the  application  of  cold 
to  the  surface,  or  the  irritation  of  the  nipple,  occasioning  a  reflex 
action  in  the  uterus.  But  it  is  probable  that  this  organ  has  also  con- 
siderable power  of  contracting,  independently  of  the  nervous  system; 
thus  there  are  w^ell-authenticated  cases  on  record,  in  which  the  foetus 
has  been  expelled  after  the  somatic  death  (§  65)  of  the  parent;  which 
must  have  been  in  consequence  of  the  persistence  of  the  independent 


470  MAMMARY  GLANDS. 

contractility  of  the  Uterus,  and  the  relaxed  state  of  all  the  parts 
through  which  the  child  had  to  make  its  exit. 

829.  The  cause  of  the  occasional  occurrence  of  the  parturient  efforts 
at  an  unusually  early  period,  is  as  little  understood  as  that  of  their 
ordinary  action.  There  are  some  individuals,  in  whom  this  regularly 
happens  at  a  certain  month ;  so  that  it  seems  to  be  an  action  natural 
to  them.  In  many  cases,  however,  it  may  be  traced  to  some  undue 
exertion  of  body,  or  mental  excitement;  and  not  unfrequently  to  a 
general  constitutional  irritability,  which  renders  the  system  liable  to 
be  deranged  by  very  trifling  causes.  Premature  labour  is  almost  always 
to  be  prevented,  if  possible;  being  injurious  alike  to  both  mother  and 
child ;  and  for  this  prevention  we  have  chiefly  to  rely  upon  rest  and 
tranquillity  of  mind  and  body,  and  upon  the  careful  avoidance  of  all 
those  exciting  causes,  which  are  liable  to  produce  uterine  contractions 
by  their  operation  upon  the  nervous  system ;  whilst,  at  the  same  time, 
any  measures  which  will  invigorate  the  body,  without  stimulating  it, 
should  not  be  overlooked. 

830.  A  peculiar  preparation  is  made,  in  the  females  of  the  class 
Mammalia,  for  the  sustenance  of  the  infant,  for  a  long  period  after 
birth.  This  consists  in  the  secretion  of  a  fluid,  from  the  glands,  termed 
Mammary^  which  contains  all  the  elements  that  are  required  for  the 
development  of  the  body  of  the  infant,  during  the  first  year.  These 
glands  present  themselves  in  an  almost  rudimentary  state,  in  some  of 
the  non-placental  animals  of  the  class  ;  consisting  only  of  a  few  large 
follicles,  which  open  separately  upon  the  surface  (Fig.  106).  In  the 
higher  Mammalia,  however,  we  find  it  composed  of  vast  numbers  of 
minute  follicles,  clustered  together  upon  excretory  ducts.  The  general 
arrangement  of  these,  in  the  human  subject,  is  seen  in  Fig.  140;  and 

in  Fig.  11 1,  the  character  of  the  follicles  them- 
F'"!"^^-  selves,  and  of  the  secreting  epithelial  cells  they 

contain,  as  seen  under  a  much  higher  magni- 
fying power,  has  been  already  shown.  Each 
Mammary  gland  consists  of  a  number  of  glan- 
dulae,  which  are  held  together  by  areolar  and 
fibrous  tissue ;  this  arrangement  may  probably 
have  reference  to  the  mobility,  which  it  is  re- 
miikXcMn^foUicirsffmrn^a  quisitc  that  the  different  parts  of  the  mass  should 
"S^^l^^^l^^s!"  possess,  one  upon  the  other,  in  consequence  of 
its  situation  upon  the  pectoralis  muscle.  The 
ducts  converge  and  unite  together;  so  as  at  last  to  form  ten  or  twelve 
principal  trunks,  which  terminate  in  the  nipple.  At  the  base  of  the 
nipple,  these  tubes  dilate  into  reservoirs,  which  extend  beneath  the 
areola,  and  to  some  distance  into  the  gland,  when  the  breast  is  in  a 
state  of  lactation.  These,  which  are  much  larger  in  many  of  the 
lower  Mammalia  than  they  are  in  the  Human  female,  seem  to  have 
for  their  office  to  contain  a  store  of  milk,  sufl^cient  to  supply  the  imme- 
diate wants  of  the  child  when  it  is  first  applied  to  the  breast;  so  that 


COMPOSITION  OF  MILK.  471 

it  shall  not  be  disappointed,  but  shall  be  induced  to  proceed  with 
sucking,  until  the  draught  be  occasioned  (§  836). 

831.  The  Mammary  gland  may  be  detected  at  an  early  period  of 
foetal  existence,  and  it  then  presents  no  difference  in  the  male  and 
female ;  and  it  continues  to  grow,  in  each  sex,  in  proportion  to  the 
body  at  large,  up  to  the  period  of  puberty.  At  that  epoch,  however, 
the  gland  begins  to  undergo  a  great  enlargement  in  the  female ;  and  by 
the  age  of  twenty,  it  attains  its  full  size  previous  to  lactation.  Even 
then,  however,  the  milk-follicles  cannot  be  injected  from  the  tubes. 
During  pregnancy,  the  mammary  glands  receive  a  greatly-increased 
quantity  of  blood.  This  determination  often  commences  very  early ; 
and  produces  a  feeling  of  tenderness  and  distension,  which  is  a  valuable 
sign  (where  it  occurs  in  conjunction  with  others)  of  conception  having 
taken  place.  The  vascularity  of  the  gland  continues  to  increase  during 
pregnancy;  and,  at  the  time  of  parturition,  its  lobulated  character  can 
be  distinctly  felt.  The  follicles  cannot  be  readily  injected,  however, 
until  the  gland  is  in  a  state  of  complete  functional  activity ;  i.  e.,  during 
lactation. — The  Mammary  gland  of  the  Male  does  not  undergo  this 
increase  of  development,  except  under  certain  peculiar  circumstances 
to  be  presently  noticed  (§  836);  and  it  remains  a  sort  of  miniature 
picture  of  that  of  the  female,  varying  in  diameter  from  that  of  a  large 
pea  to  an  inch  or  even  two  inches. 

832.  The  Milk,  secreted  by  the  Mammary  glands,  consists  of 
Water,  holding  in  solution  the  peculiar  albuminous  substance  termed 
Casein  (§  176),  and  various  Saline  ingredients,  together  with  (in 
most  cases)  a  certain  form  of  Sugar;  and  having  Oleaginous  globules 
suspended  in  it.  These  globules  appear  to  be  surrounded  by  a  thin 
pellicle,  which  keeps  them  asunder,  so  long  as  the  milk  remains  at 
rest. — The  existence  of  these  elements  in  ordinary  Milk,  as  that  of  the 
Cow,  is  made  apparent  by  the  processes  to  which  it  is  subjected  in 
domestic  economy.  If  it  be  allowed  to  stand  for  some  time,  exposed 
to  the  air,  a  large  part  of  the  oleaginous  globules  come  to  the  surface, 
in  consequence  of  their  inferior  specific  gravity ;  and  thus  is  formed 
the  creamy  which  includes  also  a  considerable  amount  of  casein,  with 
the  sugar  and  salts  of  the  milk.  These  may  be  partly  separated  by 
the  continued  agitation  of  the  cream,  as  in  the  process  of  churning; 
this,  by  rupturing  the  envelops  of  the  oil-globules,  separates  it  into 
butter,  formed  by  their  aggregation,  and  buttermilk,  containing  the 
casein,  sugar,  &c.  A  considerable  quantity  of  casein,  however,  is 
still  entangled  with  the  oleaginous  matter ;  and  this  has  a  tendency 
to  decompose,  so  as  to  render  the  butter  rancid.  It  maybe  separated 
by  keeping  the  butter  melted  at  a  temperature  of  180° ;  when  the 
casein  will  fall  to  the  bottom,  leaving  the  butter  pure  and  much  less 
liable  to  change, — an  operation  which  is  commonly  known  as  the 
clarifying  of  butter.  The  Milk,  after  the  cream  has  been  removed, 
still  contains  the  greater  part  of  its  casein  and  sugar.  If  it  be  kept 
long  enough,  a  spontaneous  change  takes  place  in  its  composition  ;  an 
incipient  change  in  the  casein  being  the  cause  of  the  conversion  of 


472  COMPOSITION  OF  MILK. 

the  sugar  into  lactic  acid ;  and  this  coagulating  the  casein,  by  pre- 
cipitating it  in  small  flakes.  The  same  precipitation  may  be  accom- 
plished at  any  time  by  the  agency  of  various  acids,  especially  the 
acetic,  which  does  not  act  upon  Albumen  ;  but  Casein  cannot  be 
coagulated  like  albumen,  by  the  influence  of  heat  alone.  The  most 
complete  coagulation  of  Casein  is  effected  by  the  agency  of  the  dried 
stomach  of  the  calf,  known  as  rennet;  which  exerts  so  powerful  an 
influence,  as  to  coagulate  the  casein  of  1,800  times  its  weight  of 
milk.  It  is  thus  that,  as  in  the  making  of  cheese,  the  curd  is  sepa- 
rated from  the  whey;  the  former  consisting  chiefly  of  the  casein; 
whilst  the  latter  contains  a  large  proportion  of  the  saline  and  saccha- 
rine matter,  which  entered  into  the  original  composition  of  the  milk. 
These  may  be  readily  separated  by  evaporation. 

833.  The  chief  characters  of  Casein  have  been  already  stated 
(§  176). — Its  Oleaginous  matter  consists,  like  the  fats  in  general,  of 
the  two  substances,  elaine  and  stearine ;  but  it  also  contains  another 
substance  peculiar  to  it,  which  is  termed  hutyrine.  This  last  (to 
which  the  characteristic  smell  and  taste  of  butter  are  due)  is  converted 
by  saponification  into  three  volatile  acids,  of  strong  animal  odour,  to 
which  the  names  of  butyric,  capric,  and  caproic  acids  have  been  given. 
This  change  may  be  effected,  at  any  period,  by  treating  the  butyrine 
with  alkalies ;  but  it  may  also  take  place  by  spontaneous  decompo- 
sition, which  is  favoured  by  time  and  moderate  warmth. — The  Sugar 
of  Milk  is  peculiar  as  containing  nearly  12  per  cent,  of  water;  so  that 
it  may  be  considered  as  really  a  hydrate  of  sugar.  It  is  nearly  iden- 
tical in  its  composition  with  starch ;  and  may,  like  it,  be  converted 
into  true  sugar  by  the  agency  of  sulphuric  acid.  But  it  is  chiefly  re- 
markable for  its  proneness  to  conversion  into  lactic  acid,  under  the 
influence  of  a  ferment  or  decomposing  azotized  substance. — The  Sa- 
line matter  contained  in  Milk  appears  to  be  nearly  identical  with  that 
of  the  blood ;  with  a  larger  proportion,  however,  of  the  phosphates  of 
lime  and  magnesia,  which  amount  to  2  or  2\  parts  in  1000.  These 
are  held  in  solution  chiefly  by  the  Casein,  which  has  a  remarkable 
power  of  combining  with  them. 

834.  Thus  ordinary  Milk  contains  the  three  classes  of  organic 
principles,  which  form  the  chief  part  of  the  food  of  animals, — namely, 
the  albuminous,  the  saccharine,  and  the  oleaginous;  together  with  the 
mineral  elements,  which  are  required  for  the  development  and  consoli- 
dation of  the  fabric  of  the  infant.  It  would  appear,  however,  that 
the  combination  of  all  these  is  not  necessary;  but  rather  has  reference 
to  the  composition  of  the  food,  on  which  the  animal  is  destined  to  be 
afterwards  supported.  Thus  it  has  been  lately  shown  that,  in  the 
Carnivora,  the  milk  contains  no  sugar  ;  which  principle  is  altogether 
wanting  in  the  food  of  the  adult.  Amongst  the  different  species  of 
Herbivorous  animals,  the  proportion  of  the  several  ingredients  varies 
considerably  ;  and  it  is  also  liable  to  considerable  variation  in  accord- 
ance with  the  nature  of  the  food,  the  amount  of  exercise  taken  by  the 
animal  that  affords  it,  and  other  circumstances.     Thus  in  the  milk  of 


COMPOSITION  AND  PRODUCTION  OF  MILK.  473 

the  Cow,  Goat,  and  Sheep,  the  average  proportions  of  Casein,  Butter, 
and  Sugar  are  nearly  the  same  one  with  another,  each  amounting  to 
from  3  to  5  per  cent.  In  the  milk  of  the  Ass  and  Mare,  on  the 
other  hand,  the  proportion  of  Casein  is  under  2  per  cent.,  the  oleagi- 
nous constituents  are  scarcely  traceable,  whilst  the  sugar  and  allied 
substances  rise  to  nearly  9  percent.  In  the  Human  female,  the  sac- 
charine and  oleaginous  elements  are  both  present  in  large  amount; 
whilst  the  Casein  forms  a  moderate  proportion. — The  proportion  of 
the  saccharine  and  oleaginous  elements  appears  to  be  considerably 
affected  by  the  amount  in  which  these  are  present  in  the  food ;  and 
by  the  degree  in  which  the  quantity  ingested  is  consumed  by  the 
respiratory  process.  Thus,  a  low  external  temperature,  and  out-door 
exercise,  by  increasing  the  production  of  carbonic  acid  from  the  lungs, 
occasion  the  consumption  of  the  oleaginous  and  saccharine  matters, 
which  might  otherwise  pass  into  the  milk,  and  thus  diminish  the 
amount  of  cream.  On  the  other  hand,  exercise  favours  the  secretion 
of  casein ;  which  would  seem  to  show,  that  this  ingredient  is  derived 
from  the  disintegration  of  the  azotized  tissues.  Thus  in  Switzerland, 
the  cattle  which  pasture  in  exposed  situations,  and  which  are  obliged 
to  use  a  great  deal  of  muscular  exertion,  yield  a  very  small  quantity 
of  butter,  but  an  unusually  large  proportion  of  Cheese ;  yet  the  same 
cattle,  when  stall-fed,  give  a  large  quantity  of  butter,  and  very  little 
cheese. 

835.  The  Milk  first  secreted  after  parturition,  known  as  the  Colos- 
trum^ is  very  different  from  ordinary  milk ;  and  possesses  a  strongly 
purgative  action,  which  is  useful  in  clearing  the  bowels  of  the  infant 
from  the  various  secretions  which  have  accumulated  in  them  at  birth^ 
constituting  the  meconium.  The  Colostrum,  when  examined  with  the 
Microscope,  is  found  to  contain  a  multitude  of  large  yellow  granulated 
corpuscles ;  each  of  which  seems  composed  of  a  number  of  small  grains 
aggregated  together.  The  colostric  character  is  sometimes  retained  for 
some  time  after  birth,  and  severely  affects  the  health  of  the  infant. 
This  may  happen  without  any  peculiarity  in  the  ordinary  characters 
of  the  secretion,  which  has  all  the  appearance  of  healthy  milk ;  but 
the  Microscope  at  once  detects  the  difference,  by  the  presence  of  the 
colostric  corpuscles. 

836.  The  formation  of  this  Secretion  is  influenced  by  the  Nervous 
system,  to  a  greater  degree,  perhaps,  than  that  of  any  other.  The 
process  may  go  on  continuously,  to  a  slight  degree,  during  the  whole 
period  of  lactation ;  but  it  is  only  in  animals  that  have  special  reser- 
voirs for  the  purpose,  that  any  accumulation  of  the  fluid  can  take 
place.  In  the  Human  female,  as  we  have  seen,  these  are  so  minute 
as  to  hold  but  a  trifling  quantity  of  milk ;  and  the  greater  part  of  the 
secretion  is  actually  formed,  whilst  the  child  is  at  the  breast.  The 
irritation  of  the  nipple  produced  by  the  act  of  suction,  and  the  mental 
emotion  connected  with  it,  concur  to  produce  an  increased  flow  of 
blood  into  the  gland,  which  is  known  to  Nurses  as  the  draught ;  and 
thus  the  secretion  is  for  the  time  greatly  augmented.     The  draught 


474  INFLUENCE  OF  FEELINGS  ON  MAMMARY  SECRETION. 

may  be  produced  simply  by  the  emotional  state  of  mind,  as  by  the 
thought  of  the  child  when  absent ;  and  the  irritation  of  the  nipple 
may  alone  occasion  it ;  but  the  two  influences  usually  act  simulta- 
neously. The  most  remarkable  examples  of  the  influence  of  such 
stimuli  on  the  Mammary  secretion,  are  those  in  which  milk  has  been 
produced  by  girls  and  old  women,  and  even  by  men,  in  quantity  suffi- 
cient for  the  support  of  an  infant.  The  application  of  the  child  to  the 
nipple  in  order  to  tranquilize  it,  the  irritation  produced  by  its  efforts 
at  suction,  and  the  strong  desire  to  furnish  milk,  seem  in  the  first 
instance  to  occasion  an  augmented  nutrition  of  the  gland,  so  that  it 
becomes  fit  for  the  performance  of  its  function ;  and  then  to  produce 
in  it  that  state  of  functional  activity,  the  result  of  which  is  the  pro- 
duction of  Milk. 

837.  It  is  not  only  in  this  way,  that  the  Mammary  secretion  is  in- 
fluenced by  the  condition  of  the  mind  ;  for  it  is  peculiarly  liable  to  be 
aflfected  as  to  quality,  by  the  habitual  state  of  the  feelings,  or  even  by 
their  temporary  excitement.  Thus  a  fretful  temper  not  only  lessens 
the  quantity  of  milk,  but  makes  it  thin  and  serous,  and  gives  it  an 
irritating  quality ;  and  the  same  effect  will  be  produced  for  a  time  by 
a  fit  of  anger.  Under  the  influence  of  grief  or  anxiety,  the  secretion 
is  either  checked  altogether,  or  it  is  diminished  in  amount,  and  dete- 
riorated in  quality.  The  secretion  is  usually  checked  altogether  by 
terror ;  and  under  the  influence  of  violent  passion,  it  may  be  so  changed 
in  its  characters,  as  to  produce  the  most  injurious  and  even  fatal  con- 
sequences to  the  infant.  So  many  instances  are  now  on  record,  in 
which  children,  that  have  been  suckled  within  a  few  minutes  after  the 
mothers  have  been  in  a  state  of  violent  rage  or  terror,  have  died  sud- 
denly in  convulsive  attacks,  that  the  occurrence  can  scarcely  be  set 
down  as  a  mere  coincidence ;  and  certain  as  we  are  of  the  deleterious 
effects  of  less  severe  emotions  upon  the  properties  of  the  milk,  it  does 
not  seem  unlikely  that,  in  these  cases,  the  bland  nutritious  fluid  should 
be  converted  into  a  poison  of  rapid  and  deadly  operation. 

838.  Of  the  quantity  of  Milk  ordinarily  secreted  by  a  good  Nurse, 
it  is  impossible  to  form  any  definite  idea ;  as  the  amount  which  can 
be  artificially  drawn,  affords  no  criterion  of  that  which  is  ordinarily 
secreted  at  the  time  of  the  draught.  The  quantity  which  can  be 
squeezed  from  either  breast  at  any  one  time,  and  which,  therefore, 
must  have  been  contained  in  its  tubes  and  reservoirs,  is  about  two 
ounces.  The  amount  secreted  will  depend  upon  several  circum- 
stances ;  such  as  the  nature  and  amount  of  the  ingesta ;  the  state  of 
bodily  health  ;  and  the  condition  of  the  mind.  An  adequate  but  not 
excessive  amount  of  nutritious  food,  in  which  the  farinaceous,  olea- 
ginous, and  albuminous  principles  are  duly  blended ;  a  vigorous  but 
not  plethoric  constitution,  regular  habits,  and  moderate  exercise ; 
together  with  a  cheerful  and  tranquil  temper ;  altogether  produce  the 
most  beneficial  influence  upon  the  secretion.  It  is  seldom  that  stimu- 
lating liquors,  which  are  so  commonly  indulged  in,  are  anything  but 
prejudicial ;  but  the  unmeasured  condemnation  of  them,  in  which 


ELEMENTS  OF  MILK  PRE-EXISTENT  IN  BLOOD.  475 

some  writers  have  indulged,  is  certainly  injudicious ;  as  experience 
amply  demonstrates  the  improvement  in  the  condition  both  of  mother 
and  infant,  which  occasionally  results  from  the  moderate  employment 
of  them. — In  the  administration  of  medicines  to  the  mother,  it  is 
very  desirable  that  the  tendency  of  soluble  saline  substances  to  pass 
into  the  milk,  and  thus  to  affect  the  child,  should  be  borne  in  mind. 
The  vegetable  substances  used  in  medicine  seem  to  have  much  less 
disposition  to  pass  off  by  this  secretion ;  and  they  are  consequently 
to  be  preferred  during  lactation. 

839.  From  the  close  correspondence  which  exists  between  the  ele- 
ments of  the  Milk  and  those  of  the  Blood,  it  is  evident  that  we  cannot 
expect  to  trace  the  existence  of  the  former,  as  such,  in  the  circulating 
current.  It  is  interesting,  however,  to  remark,  that  a  preparation  ap- 
pears to  be  taking  place  in  the  laboratory  of  the  system,  for  the  pro- 
duction of  this  secretion,  long  before  the  period  of  parturition.  The 
Urine  of  pregnant  women  almost  invariably  contains  a  peculiar  sub- 
stance termed  kiestine,  which  is  nearly  related  to  casein,  and  which 
disappears  from  the  urine  as  soon  as  lactation  has  fully  commenced. 
It  would  seem,  therefore,  that  a  compound  of  this  nature  is  in  course 
of  preparation  during  pregnancy  ;  and  that  it  is  eliminated  by  the 
kidney  until  the  Mammary  Gland  is  prepared  for  the  active  perform 
ance  of  its  function. — That  the  kidney  may  relieve  the  system  from 
the  accumulation  of  other  constituents  of  the  mammary  secretion,  ap- 
pears from  a  case  recently  put  on  record  ;  in  which  the  urine  of  a  par- 
turient female,  who  did  not  suckle  her  infant,  was  found  to  contain  a 
considerable  quantity  of  butyric  acid,  during  several  days.  There 
can  be  no  doubt  that  in  ordinary  states  of  the  system,  this  secretion 
cannot  be  required  for  the  depuration  of  the  blood  ;  since  it  does  not 
occur  in  the  male  at  all,  and  is  present  in  the  female  at  particular  times 
only.  But  these  facts  afford  ground  to  believe  that,  when  the  process 
is  going  on,  certain  products  are  generated  in  the  system,  which  are 
not  found  there  at  other  times.  And  it  is  quite  certain  that  the  sud- 
den checking  of  the  secretion,  or  the  re-absorption  of  the  fluid  already 
poured  out,  occasioning  an  accumulation  of  these  substances  in  the  cir- 
culating current,  may  give  rise  to  very  injurious  consequences.  Some 
very  curious  instances  are  on  record,  in  which  a  transference  of  the 
secreting  power  to  some  other  surface  has  taken  place  under  such  cir- 
cumstances ;  so  as  to  relieve  the  system  from  the  accumulation  in 
question. 


476  GENERAL  FUNCTIONS  OF  NERVOUS  SYSTEM, 


CHAPTER  XII. 

OF  1"HE  NERVOUS  SYSTEM. 

1,   General  View  of  the  operations,  of  which  the  JVervous  System  is  the 

instrument. 

840.  We  have  now  considered  the  entire  series  of  those  operations, 
which  niake  up  the  vegetative  or  organic  life  of  the  Animal;  including 
the  functions  by  which  the  germ  is  prepared,  by  which  it  is  nourished 
until  it  can  be  left  to  its  own  powers,  by  which  its  continued  deve- 
lopment is  effected  until  the  fabric  characteristic  of  the  adult  has  been 
built  up,  and  by  which  the  normal  constitution  is  maintained  through 
a  lengthened  period, — so  long  as  the  necessary  materials  are  supplied, 
and  no  check  or  hindrance  is  interposed,  by  external  influences,  to  that 
regular  sequence  of  change,  on  which  the  continuance  of  its  powers 
depends.  In  this  survey  it  will  have  been  perceived,  that  the  essential 
parts  of  these  operations  are,  in  Animals  as  in  Plants,  completely 
independent  of  the  influence  of  that,  which  constitutes  the  peculiar 
endow^ment  of  Animals;  namely,  the  Nervous  System. 

a.  The  Reduction  of  the  food  in  the  Stomach,  by  the  solvent  power 
of  the  gastric  fluid,  is  a  purely  chemical  operation,  with  which  the 
Nervous  System  has  nothing  whatever  to  do,  excepting  that  it  per- 
haps accelerates  the  process,  by  stimulating  the  Muscular  coat  of  the 
stomach  to  that  peculiar  series  of  contractions,  which  keeps  the  con- 
tents of  the  cavity  in  continual  movement,  and  favours  the  action  of 
the  solvent  upon  it. 

b.  With  the  process  of  Absorption,  by  which  the  nutritive  materials, 
with  other  substances,  are  introduced  into  the  vessels,  the  Nervous 
System  has  nothing  to  do  ;  this  being  a  purely  vegetative  operation, 
partly  dependent  upon  the  simple  physical  conditions  which  produce 
Endosmose,  and  partly  on  a  process  of  cell-growth. 

c.  The  Assimilation  of  the  new  material,  effected,  as  we  have  seen 
reason  to  believe,  by  another  set  of  independent  cells,  can  receive  but 
little  influence  from  the  Nervous  System,  and  is  obviously  capable 
of  taking  place  without  its  aid. 

d.  The  Circulation  of  the  Blood,  again,  though  dependent  in  part 
upon  the  impulsive  power  of  a  Muscular  organ,  the  Heart,  is  not  on 
that  account  brought  into  closer  dependence  upon  the  Nervous  System; 
for  we  have  seen  that  the  contractions  of  the  heart  result  from  its  own 
inherent  powers,  so  as  to  continue  after  it  has  been  completely  de- 
tached from  the  body  ;  and  that  the  capillary  power,  which  is  the  chief 
agent  in  the  movement  of  the  blood  in  the  lower  animals,  and  which 
exerts  an  important  subsidiary  action  in  the  higher,  is  the  result  of 


GENERAL  FUNCTIONS  OF  NERVOUS  SYSTEM.  477 

the  exercise  of  certain  affinities,  between  the  blood  and  the  surround- 
ing tissues,  in  which  the  Nervous  System  can  have  no  immediate 
concern. 

e.  The  act  of  JVutrition,  in  which  every  tissue  draws  from  the  cir- 
culating blood  the  materials  for  its  own  continued  growth  and  deve- 
lopment, and  by  which  it  incorporates  these  with  its  own  substance, 
is  but  a  continuance  of  the  same  kind  of  operation,  as  that  which 
takes  place  in  the  early  development  of  the  embryo,  long  anteriorly  to 
the  first  appearance  of  the  nervous  system, — namely,  a  process  of  cell- 
development  and  metamorphosis,  which  must  be,  from  its  very  nature, 
independent  of  Nervous  agency. 

y.  The  same  may  be  said  of  the  Secreting  operation  in  general ;  for 
this  essentially  consists  of  the  separation  of  certain  products  from  the 
blood,  by  cells  situated  upon  free  surfaces;  which  thus  remove  those 
products  from  the  interior  of  the  fabric. 

g.  And  the  interchange  of  oxygen  and  carbonic  acid,  w^hich  takes 
place  between  the  atmosphere  and  the  venous  blood,  when  brought 
into  mutual  relation  in  the  lungs,  and  which  is  the  essential  part  of  the 
function  of  Respiration^  is  an  operation  of  a  merely  physical  character, 
with  which  the  Nervous  system  can  have  no  direct  concern. 

h.  Finally,  the  development  of  the  reproductive  germs  in  the  one 
sex,  and  of  the  ova  within  which  these  are  to  be  evolved  in  the  other, 
the  subsequent  fertilization  of  the  latter  by  the  former,  and  the  changes 
consequent  upon  that  act,  together  making  up  the  function  of  Repro- 
duction, may  be  all  regarded  as  modifications  of  the  ordinary  Nutri- 
tive processes;  and  are  effected,  like  these,  by  the  inherent  powers 
of  the  parts  concerned  in  them,  at  the  expense  of  the  materials  sup- 
plied by  the  blood,  without  any  direct  dependence  upon  the  Nervous 
system. 

841.  Still,  although  the  various  processes,  which  make  up  the  essen- 
tial part  of  the  nutritive  operations,  in  Animals  as  in  Plants,  are  no 
more  dependent  on  any  peculiar  influence  derived  from  a  Nervous 
system,  in  the  former,  than  they  are  in  the  latter,  it  must  be  evident, 
from  the  details  already  given,  that  there  must  be  in  Animals  various 
accessory  changes,  which  are  requisite  for  the  continuance  of  the 
former,  and  which  can  only  be  effected  by  the  peculiar  powers  with 
which  Animals  are  endowed. — Thus,  to  commence  with  Digestion  ; — 
this  preliminary  process,  which  the  nature  of  the  food  of  the  plant 
renders  unnecessary  {ox  its  maintenance,  can  only  be  accomplished  by 
the  introduction  of  the  food  into  a  cavity  or  sac,  in  which  it  may  be 
submitted  to  the  action  of  the  solvent  fluid.  The  operation  o{ grasp- 
ing and  swallowing  the  food,  wherever  it  is  performed,  is  accomplished 
through  the  agency  of  the  Nervous  system ;  and  if  it  be  checked  by 
the  loss  of  Nervous  power,  the  Digestive  process  must  cease  for  want 
of  material. — So,  again,  although  interchange  of  gaseous  ingredients 
between  the  atmosphere  and  the  circulating  fluid  may  take  place  with 
sufficient  energy  in  Plants  and  the  lower  Animals,  through  the  mere 
exposure  of  the  general  surface  to  the  atmosphere,  yet  w^e  find  that, 


478         SHARE  OF  NERVOUS  SYSTEM  IN  ORGANIC  FUNCTIONS. 

in  all  the  higher  Animals,  certain  movements  are  requisite,  for  the  con- 
tinual renewal  of  the  air  or  water  which  are  in  contact  with  one  side 
of  the  respiratory  surface,  and  of  the  blood  which  is  in  relation  with 
the  other :  for  the  direction  of  which  movements,  a  Nervous  system 
is  requisite. — In  the  excretory  processes,  moreover,  the  removal  of  the 
effete  matters  from  the  body  can  only  be  accomplished,  in  the  higher 
Animals,  by  certain  combined  movements;  the  object  of  which  is  to 
take  up  the  products  that  are  separated  by  the  action  of  the  proper 
secreting  cells,  and  to  carry  them  to  the  exterior  of  the  body,  there 
to  be  set  free  ;  and  these  combined  movements  can  only  be  effected 
by  the  agency  of  the  Nervous  system. — Lastly,  in  the  act  of  Repro- 
duction, the  arrangement  of  the  sexual  organs  in  Animals,  requires 
that  a  certain  set  of  movements  should  be  adapted  to  set  free  the  germ 
from  the  body  of  the  male,  and  to  convey  it  to  the  ovule  of  the  fe- 
male; and  further,  that  the  ovum  should  be  expelled  from  the  body 
of  the  latter,  in  a  state  of  more  or  less  advanced  development.  For 
these  movements  a  special  arrangement  is  made,  in  the  construction 
of  the  Nervous  system,  and  in  the  application  of  its  peculiar  powers. 
842.  Thus  we  see  that,  although  the  Organic  functions  of  the  Ani- 
mal are  essentially  independent  of  the  Nervous  System,  this  system 
affords  the  conditions  which  are  requisite  for  their  continued  main- 
tenance ;  being  the  instrument  by  which  the  muscles  are  called  into 
action  for  the  performance  of  the  various  combined  actions  that  con- 
stitute the  mechanism  (so  to  speak),  by  which  the  Vegetative  part  of 
the  fabric  is  combined  w^ith  the  Animal  portion  of  the  organism.  We 
are  not  to  suppose,  however,  that  every  movement  which  takes  place 
in  the  Animal  body  is  dependent  upon  the  Nervous  System  ;  for  we 
have  seen  that  the  Muscular  tissue  may  be  employed  to  perform  con- 
tractions excited  by  stimuli  applied  to  itself,  and  that  it  may  thus 
execute  a  set  of  movements  in  which  the  nervous  system  has  no  di- 
rect participation.  And  it  is  desirable  that  the  Student  should  ob- 
serve, that  these  are,  in  all  instances,  those  most  directly  connected 
with  the  Vegetative  functions,  and,  at  the  same  time,  those  of  the 
simplest  and  most  straightforward  character. — Thus,  the  peristaltic 
movement,  by  which  the  alimentary  and  fecal  matters  are  propelled 
along  the  Intestinal  tube,  results  from  the  direct  excitement  of  the 
contractility  of  its  muscular  walls,  and  is  entirely  independent  of 
Nervous  agency  ;  and  this  movement  is  accomplished  by  the  succes- 
sive contraction  of  the  different  fasciculi  surrounding  the  tube,  which 
take  up  (as  it  were)  each  other's  action  (§  352).  So,  again,  the  suc- 
cessive contractions  and  dilatations  of  the  cavities  of  the  Heart,  which 
perform  so  important  a  part  in  the  Circulation  of  the  blood,  are  the 
result  of  the  properties  inherent  in  that  organ  ;  the  muscular  fibres  of 
which  are  excited  to  a  peculiar  rhythmical  and  consentaneous  con- 
traction, by  the  flow  of  blood  into  the  cavities  when  dilating.  More- 
over, in  the  Excretory  ducts  of  various  glands,  we  find  a  Muscular 
coat,  by  which  the  fluids  secreted  in  the  glands,  are  propelled  towards 


GENERAL  FUNCTIONS  OF  NERVOUS  SYSTEM.  479 

their  outlet  on  the  exterior  of  the  body,  or  on  one  of  its  free  internal 
surfaces. 

843.  In  these  instances,  then,  we  observe  that  the  simple  Contrac- 
tility of  Muscular  structure,  excited  by  direct  stimulation,  is  applied 
to  effect  the  movements  most  closely  connected  with  the  Organic 
functions.  With  the  processes,  therefore,  which  take  place  in  the 
penetralia  of  the  system,  the  Nervous  System  has  no  direct  concern. 
Its  office  is  to  guard  the  portals  for  entrance  and  exit ;  and  to  fill 
those  chambers,  which  admit  the  new  materials  from  the  external 
world  ;  or  to  empty  the  receptacles,  which  collect  from  the  interior  of 
the  system  the  effete  matters  that  are  to  be  cast  out  from  it.  And  we 
find  that,  for  these  offices,  the  Nervous  system  is  employed  in  its  very 
simplest  mode  of  operation  ; — that  which  does  not  involve  Sensation, 
Intelligence,  Will,  or  even  Instinct  (in  the  proper  sense  of  that  term), 
but  which  may  take  place  independently  of  all  consciousness, — by  the 
simple  reflexion  of  an  impression,  conveyed  to  a  ganglionic  centre  by 
one  set  of  fibres  proceeding  towards  it  from  the  circumference  along 
another  set  which  passesyrom  it  to  the  muscles,  and  calls  them  into 
operation  (§  394).  This  reflex  function,  therefore,  is  the  simplest 
application  of  the  Nervous  System  in  the  Animal  body.  We  shall 
presently  see  reason  to  believe,  that  a  very  large  proportion  of  the 
movements  of  many  of  the  lower  animals  are  of  this  reflex  character  ; 
and  that  they  are  not  necessarily  accompanied  by  sensation,  although 
this  may  usually  be  aroused  by  the  same  cause  which  produces  them. 
As  we  rise,  however,  in  the  scale  of  Animal  existence,  we  find  the 
reflex  movements  forming  a  smaller  and  smaller  proportion  of  the 
whole  ;  until,  in  Man,  they  constitute  so  limited  a  part  of  the  entire 
series  of  movements  of  which  the  Nervous  system  is  the  agent,  that 
their  very  existence  has  been  overlooked. 

844.  But  the  main  purpose  of  the  Nervous  System  is  to  serve  as 
the  instrument  of  the  Psychical*  powers,  which  are  the  distinguishing 
attribute  of  the  Animal.  It  has  been  already  pointed  out,  that  the  pos- 
session of  Consciousness  (or  of  the  capability  of  receiving  sensations), 
and  the  power  of  executing  Spontaneous  Movements  (that  is,  move- 
ments which  are  not  immediately  dependent  upon  external  stimuli),  con- 
stitute the  essential  features  in  which  the  Animal  differs  from  the  Plant. 
All  the  other  differences  in  structure,  that  respectively  characterize 
these  two  classes  of  living  beings,  are  subordinate  to  this  one  leading 
distinction, — the  presence  of  a  Nervous  system,  and  of  its  peculiar 
attributes  in  the  one, — and  its  absence  in  the  other.  Now  when  we 
attempt  to  analyze  these  peculiar  attributes,  we  may  resolve  them, 
like  the  properties  of  the  material  body,  into  different  groups.  We 
find  that  the  first  excitement  of  all  mental  changes,  whether  these 
involve  the  action  of  (he  Jeelings  or  of  the  reason,  depends  upon  sen- 
sations ;  which  are  produced  by  impressions  made  upon  the  nerves  of 

*  This  term,  derived  from  the  Greek  ^-w^"*  is  used  to  designate  the  sensorial  and 
mental  endowments  of  Animals,  in  the  most  comprehensive  acceptation  of  those 
terms. 


480         DEPENDENCE  OF  MENTAL  ACTIONS  UPON  SENSATION. 

certain  parts  of  the  body,  and  are  conveyed  by  these  to  a  particular 
ganglionic  centre,  which  is  termed  the  sensorium, — being  the  part  in 
which  Sensation,  or  the  capability  oi  feeling  external  impressions, 
especially  resides. 

845.  Now  there  are  numerous  actions,  especially  among  the  lower 
Animals,  which  seem  to  be  as  far  removed  from  the  influence  of  the 
Will,  and  as  little  directed  by  Intelligence,  as  the  Reflex  movements 
themselves  ;  but  which,  nevertheless,  depend  upon  sensation  for  their 
excitement.  The  sensation  may  immediately  direct  the  movement ; 
or  it  may  excite  an  emotion  or  desire,  which,  without  any  calculation 
of  consequences,  any  intentional  adaptation  of  means  to  ends,  any 
exertion  of  the  reason,  or  any  employment  of  a  discriminating  Will, 
may  produce  an  action,  or  train  of  actions,  as  directly  and  obviously 
adapted  to  the  well-being  of  the  individual,  as  we  have  seen  those  of 
the  reflex  character  to  be.  It  is  impossible  to  say,  in  regard  to  many 
of  the  actions  of  the  lower  animals,  to  what  extent  they  involve  feel- 
ings or  emotions,  at  all  analogous  to  those  which  we  experience  ;  and 
it  would  seem  better  to  apply  the  generic  term  Consensual  to  those  in 
which  the  Sensation  excites  the  motor  action,  either  immediately,  or 
through  the  agency  of  an  indiscriminating  Desire  excited  by  the  sen- 
sation. This  class  will  include  all  the  purely  Instinctive  actions  of 
the  low^er  Animals  ;  which  make  up,  with  the  reflex,  nearly  the  whole 
of  the  Animal  functions  in  many  tribes ;  but  which  are  found  to  be 
gradually  brought  under  subordination  to  the  Intelligence  and  Will, 
as  we  rise  towards  Man,  in  whom  those  faculties  are  most  strongly 
developed,  so  as  to  keep  the  Consensual  as  well  as  the  Reflex  actions 
quite  in  subordination  to  the  more  elevated  purposes  of  his  existence. 

846.  There  are  many  sensations,  however,  which  do  not  thus  im- 
mediately give  rise  to  muscular  movements ;  their  operation  being 
rather  that  of  stimulating  to  action  the  Intellectual  powers.  There 
can  be  little  doubt  that  all  Mental  processes  are  dependent,  in  the  first 
instance,  upon  Sensations ;  which  serve  to  the  Mind  the  same  kind  of 
purpose,  that  food  and  air  fulfil  in  the  economy  of  the  body.  If  we 
could  imagine  a  being  to  come  into  the  world  with  its  mental  faculties 
fully  prepared  for  action,  but  destitute  of  any  power  of  receiving  sen- 
sations, these  faculties  would  never  be  aroused  from  the  condition  in 
which  they  are  in  profound  sleep  ;  and  the  being  must  remain  in  a 
state  of  complete  unconsciousness,  because  there  is  nothing  of  which 
it  can  be  made  conscious,  no  kind  of  idea  which  can  be  aroused 
within  it.  But  after  the  mind  has  once  been  in  active  operation,  the 
destruction  of  all  future  power  of  receiving  sensations  would  not 
reduce  it  again  to  the  inactive  condition.  For  sensations  are  so  stored 
up  in  the  mind,  by  the  power  of  Memory,  that  they  may  give  rise  to 
ideas  at  any  future  time ;  and  thus  the  mind  may  feed  (as  it  were) 
upon  the  past.  Now  the  ideas  which  are  excited  by  sensations,  and 
which  are  coloured  by  the  state  of  Feeling  which  accompanies  them, 
become  the  subjects  of  Reasoning  processes  more  or  less  complex, 
sometimes  of  the  utmost  brevity  and  simplicity,  sometimes  of  the  most 


I 


CLASSIFICATION  OF  ACTIONS  OF  NERVOUS  SYSTEM.  481 

refined  and  intricate  nature.  These  reasoning  processes,  when  they 
result  in  a  determination  to  execute  a  particular  movement,  execute 
that  movement  by  an  act  of  Volition  ;  the  peculiar  character  of  which 
is,  that  it  is  the  expression  of  a  definite  purpose,  of  a  designed  adapta- 
tion of  means  to  ends,  on  the  part  of  the  individual  performing  it ; 
instead  of  being  the  result  of  mere  blind  indiscriminating  impulse, 
which  seems  to  be  the  main-spring  of  the  instinctive  operations.  It 
is  in  Man,  that  we  find  the  highest  development  of  the  reasoning 
faculties ;  but  it  is  quite  absurd  to  limit  them  to  him,  as  some  have 
done  ;  since  no  impartial  observer  can  doubt,  that  many  of  the  lower 
animals  can  execute  reasoning  processes,  as  complete  in  their  way  as 
those  of  Man,  though  much  more  limited  in  their  scope. 

847.  Thus,  then,  we  have  to  consider  the  Nervous  system  under 
three  heads  ;— first,  as  the  instrument  of  the  Reflex  actions  ; — second, 
as  the  instrument  of  the  Consensual  and  Instinctive  actions ; — third, 
as  the  instrument  of  the  Intellectual  processes,  and  of  Voluntary 
movements.  Now  there  is  good  reason  to  believe,  that  to  each  of 
these  groups  of  actions  a  particular  portion  of  the  Nervous  Centres, 
with  its  afferent  and  efferent  nerves,  may  be  assigned  ; — one  ganglion, 
or  collection  of  ganglia,  being  the  instrument  of  the  Reflex  actions; 
another  of  the  Consensual  and  Instinctive  operations ;  and  a  third  of 
the  Intellectual  powers,  and  of  the  Voluntary  movements  to  w^hich 
they  give  rise.  In  order  that  the  relations  of  these  subdivisions  may 
be  better  understood,  it  will  be  desirable  to  take  a  brief  survey  of  the 
comparative  structure  of  the  Nervous  system  in  the  principal  groups 
of  Animals;  and  to  inquire  what  actions  may  be  justly  attributed  to 
its  several  parts  in  each  instance  ;  commencing  with  those  in  which 
the  structure  is  the  simplest,  and  the  variety  of  actions  the  smallest; 
and  passing  on  gradually  to  those,  in  which  the  structure  is  increased 
in  complexity  by  the  addition  of  new  and  distinct  parts,  and  in  which 
the  actions  present  a  corresponding  variety. 

2.   Comparative  Structure  and  Actions  of  the  Jfervous  System. 

848.  From  what  has  been  already  said  (§  373-9)  of  the  characters 
of  the  two  elementary  forms  of  the  Nervous  Tissue,  it  is  evident  that 
no  Nervous  System  can  exist,  in  which  both  these  forms  should  not 
be  present.  We  look,  therefore,  for  ganglia,  composed  of  the  vesi- 
cular nervous  substance,  and  serving  as  the  centres  of  nervous 
power;  and  for  cords  or  trunks,  composed  of  the  tubular  substance, 
and  serving  to  communicate  between  the  ganglia  and  the  parts  with 
which  they  are  to  be  functionally  connected.  Now  it  is  quite  certain 
that,  at  present,  no  such  Nervous  apparatus  can  be  detected  in  many 
of  the  lowest  Animals  ;  and  some  Physiologists  have  had  recourse  to 
the  supposition  of  their  possessing  a  "  diffused"  nervous  system, — 
that  is,  of  their  possessing  nervous  particles,  in  a  separate  form,  in- 
corporated as  it  were  with  their  tissues.  But  we  have  seen,  that  each 
tissue  possesses  its  own  properties,  and  can  perform  its  own  actions, 

31 


482  NERVOUS  SYSTEM  OF  LOWEST  ANIMALS. 

independently  of  the  rest; — that  even  the  contractility  of  Muscular 
fibre  is  by  no  means  dependent  upon  the  Nervous  system,  though 
usually  called  into  play  through  its  means  ; — and  that  the  simplest 
office  of  a  Nervous  System  is  to  produce  a  muscular  movement  in 
respondence  to  a  certain  impression  ;  which  action  requires  that  it 
should  have  an  internuncial  or  communicating  power,  only  to  be  ex- 
ercised (so  far  as  we  at  present  know)  by  continuous  fibres.  The 
apparent  absence  of  a  Nervous  system  is  doubtless  to  be  attributed, 
in  many  instances,  to  the  general  softness  of  the  tissues  of  the  body, 
which  prevents  it  from  being  clearly  made  out  among  them.  And  it 
is  to  be  remembered,  that,  on  the  principles  already  stated,  we  should 
expect  to  find  it  bearing  a  much  smaller  proportion  to  the  entire 
structure,  in  the  lowest  Animals,  whose  functions  are  chiefly  Vegeta- 
tive,— than  in  the  highest,  in  which  the  vegetative  functions  seem 
destined  merely  for  the  development  of  the  Nervous  and  Muscular 
systems,  and  for  the  sustenance  of  their  powers. 

849.  Among  the  Radiated  classes,  the  parts  of  whose  bodies  are 
arranged  in  a  circular  manner  around  the  mouth,  and  repeat  each 
other  more  or  less  precisely,  the  Nervous  system  presents  a  corre- 
sponding form.  In  the  Star-fish,  for  example,  which  is  one  of  the 
highest  of  these  animals,  it  forms  a  ring,  which  surrounds  the  mouth  ; 
this  ring  consists  of  nervous  cords,  which  form  communications 
between  the  several  ganglia,  one  of  which  is  placed  at  the  base  of 
each  ray.  The  number  of  these  ganglia  corresponds  with  that  of  the 
rays  or  arms  ;  being  five  in  the  common  Star-fish ;  and  from  nine  to 
fifteen^  in  the  species  possessing  those  several  numbers  of  members. 
The  ganglia  appear  to  be  all  similar  to  one  another  in  function,  as 
they  are  in  the  distribution  of  their  branches ;  every  one  of  them 
sending  a  large  trunk  along  its  own  ray,  and  two  small  filaments  to 
the  organs  in  the  central  disk.  The  rays  being  all  so  similar  in 
structure,  as  to  be  exact  repetitions  of  each  other,  it  would  appear 
that  none  of  the  ganglia  can  have  any  controlling  power  over  the 
rest.  All  the  rays  (in  certain  species)  have  at  their  extremities  what 
seem  to  be  very  imperfect  eyes  ;  and  so  far  as  these  can  aid  in  direct- 
ing the  movements  of  the  animal,  it  is  obvious  that  they  will  do  so 
towards  all  sides  alike.  Hence  there  is  no  one  part,  which  corre- 
sponds to  the  head  of  higher  animals  ;  and  the  ganglia  of  the  nervous 
system,  like  the  parts  they  supply,  are  but  repetitions  of  one  another, 
and  are  capable  of  acting  quite  independently.  Each  would  perform 
its  own  individual  functions  if  separated  from  the  rest ;  but,  in  the 
entire  animal,  their  actions  are  all  connected  with  others  by  the  circular 
cord,  which  passes  from  every  one  of  the  five  ganglia  to  those  on 
either  side  of  it.  We  shall  find  that,  in  Articulated  and  Vertebrated 
animals,  there  is  a  similar  repetition  of  corresponding  ganglia,  on  the 
two  sides  of  the  median  plane  of  the  body  ;  and  that  these  are  con- 
nected by  transverse  bands,  analogous  in  function  to  the  circular  cord 
of  the  Star-fish.  Moreover,  we  shall  see  a  like  repetition  of  ganglia, 
almost  or  precisely  similar  in  function,  in  passing  from  one  extremity 


1 


I 


NERVOUS  SYSTEM  OF  RADIATA  AND  MOLLUSCA.  483 

of  these  animals  to  the  other  ;  and  these  ganglia  are  connected  by  lon- 
gitudinal cords,  whose  function  is  in  like  manner  commissural. — From 
the  best  judgment  we  can  form  of  the  actions  of  the  Star-fish,  by  com- 
paring them  with  the  corresponding  actions  of  higher  animals,  we 
may  fairly  regard  the  greater  number  of  them  as  simply  reflex  ;  being 
performed  in  direct  respondence  to  external  stimuli,  the  impression 
made  by  which  is  propagated  to  one  or  more  of  the  ganglia,  and  ex- 
cites in  them  a  motor  impulse.  How  far  the  movements  of  these 
animals  are  indicative  of  sensation^  we  have  not  the  power  of  deter- 
mining; but  it  may  be  safely  affirmed,  that  they  afford  very  little 
indication,  if  any,  of  the  exercise  of  reasoning  faculties,  or  of  volun- 
tary power. 

850.  Perhaps  the  simplest  form  of  a  Nervous  system  is  that  pre- 
sented by  certain  of  the  lower  Mollusca ;  for  here,  the  body  not  pos- 
sessing any  repetition  of  similar  parts,  the  nervous  system  is  destitute 
of  that  multiplication  of  ganglia  which  we  see  in  the  Star-fish  ;  whilst 
the  limited  nature  of  the  animal  powers  involves  a  corresponding  sim- 
plicity in  the  integral  parts  of  their  instrument.  The  animals,  to 
which  reference  is  here  made,  form  the  class  Tunicata;  which  is  inter- 
mediate, in  many  respects,  between  the  ordinary  Mollusks  and  the 
Zoophytes.  They  consist  essentially  of  an  external  membranous  bag 
or  tunic  ;  within  which  is  a  muscular  envelop  ;  and  within  this,  again, 
a  respiratory  sac,  which  may  be  considered  as  the  dilated  pharynx  of 
the  animal.  At  the  bottom  of  this  last,  is  the  entrance  to  the  stomach; 
which,  with  the  other  viscera,  lies  at  the  lower  end  of  the  muscular 
sac.  The  external  envelops  have  two  orifices  ;  a  mouth,  to  admit 
water  into  the  pharyngeal  sac ;  and  an  anal  orifice,  for  the  expulsion 
of  the  water  which  has  served  for  respiration,  and  of  that  which  has 
passed  through  the  alimentary  canal,  together  with  the  fecal  matter, 
the  ova,  &c.  A  current  of  water  is  continually  being  drawn  into  the 
pharyngeal  sac,  by  the  action  of  the  cilia  that  line  it;  and  of  this,  a 
part  is  driven  into  the  stomach,  conveying  to  it  the  necessary  supply 
of  aliment  in  a  very  finely  divided  state ;  whilst  a  part  is  destined 
merely  for  the  aeration  of  the  circulating  fluid,  and  is  transmitted 
more  directly  to  the  anal  orifice,  after  having  served  that  purpose. 
These  animals  are  for  the  most  part  fixed  to  one  spot,  during  all  but 
the  earliest  period  of  their  existence;  and  they  give  but  little  external 
manifestation  of  life,  beyond  the  continual  entrance  and  exit  of  the 
currents  already  adverted  to,  which,  being  eflfected  by  ciliary  action,  is 
altogether  independent  of  the  nervous  system  (§  224).  When  any 
substance  is  drawn  in  by  the  current,  however,  the  entrance  of  which 
would  be  injurious,  it  excites  a  general  contraction  of  the  mantle  or 
muscular  envelop ;  and  this  causes  a  jet  of  water  to  issue  from  one  or 
both  orifices,  which  carries  the  oflfending  body  to  a  distance.  And, 
in  the  same  manner,  if  the  exterior  of  the  body  be  touched,  the 
mantle  suddenly  and  violently  contracts,  and  expels  the  contents  of 
the  sac. 

851.  These  are  the  only  actions,  so  far  as  we  know,  which  the 


484  NERVOUS  SYSTEM  OF  MOLLUSCA. 

Nervous  system  of  these  animals  is  destined  to  perform.  They  do  not 
exhibit  the  least  trace  of  eyes,  or  of  other  organs  of  special  sense ;  and 
the  only  parts  that  appear  peculiarly  sensitive,  are  the  small  tentacula 
or  feelers,  that  guard  the  oral  orifice.  Between  the  two  apertures  in 
the  mantle,  we  find  a  solitary  ganglion,  which  receives  branches  from 
both  orifices,  and  sends  others  over  the  muscular  sac.  This,  so  far  as 
we  know  at  present,  constitutes  the  whole  nervous  system  of  the 
animal ;  and  it  is  fully  sufficient  to  account  for  the  movements  which 
have  been  described.  For  the  impression  produced  by  the  contact  of 
any  hard  substance  with  the  tentacula,  or  with  the  general  surface  of 
the  mantle,  being  conveyed  by  the  afferent  fibres  of  this  ganglion,  will 
excite  in  it  a  reflex  motor  impulse  ;  which,  being  transmitted  to  the 
muscular  fibres  of  the  contractile  sac,  as  well  as  to  those  circular  bands 
that  surround  the  orifices  and  act  as  sphincters,  will  produce  the 
movements  in  question. 

852.  In  the  Conchifera,  or  Mollusks  inhabiting  bivalve  shells,  there 
are  invariably  two  ganglia,  having  diflferent  functions.  The  larger  of 
these  (Plate  II,  Fig.  1,  c),  corresponding  to  the  single  ganglion  of  the 
Tunicata,  is  situated  towards  the  posterior  end  of  the  body  (that  is, 
the  end  most  distant  from  the  mouth),  in  the  neighbourhood  of  the 
posterior  muscle  that  draws  the  valves  together;  and  its  branches  are 
distributed  to  that  muscle,  to  the  mantle,  to  the  gills  {d,  d)^  and  to 
the  siphons  (e,  e),  by  which  the  water  is  introduced  and  carried  oflf. 
But  we  find  another  ganglion,  or  rather  pair  of  ganglia  (a,  a),  situated 
near  the  front  of  the  body,  either  upon  the  oesophagus,  or  at  its  sides; 
these  ganglia  are  connected  with  the  very  sensitive  tentacula,  which 
guard  the  mouth  ;  and  they  may  be  regarded  as  presenting  the  first 
approach,  both  in  position  and  functions,  to  the  brain  of  higher  ani- 
mals. In  the  Oyster,  and  others  of  the  lower  Conchifera,  which 
have  no  foot,  these  are  the  only  principal  ganglia ;  but  in  those  hav- 
ing a  foot, — which  is  a  muscular  tongue-like  organ, — we  find  an  addi- 
tional ganglion  (6)  connected  with  it.  This  is  the  case  in  the  Solen, 
or  animal  of  the  Razor-shell  ;  whose  foot  is  a  very  powerful  boring- 
instrument,  enabling  it  to  penetrate  deeply  into  the  sand. — Here,  then, 
we  have  three  distinct  kinds  of  ganglionic  centres;  every  one  of  which 
may  be  doubled,  or  repeated  on  the  two  sides  of  the  body.  First,  the 
cephalic  ganglia,  a,  a,  which  are  probably  the  sole  instruments  of  sen- 
sation and  of  the  consensual  movements;  as  well  as  of  whatever  i;o/m7i- 
tary  power  the  animal  may  possess  :  these  are  almost  invariably 
double,  being  connected  together  by  a  transverse  band,  which  arches 
over  the  oesophagus.  Second,  the  pedal  ganglion,  h,  which  is  usually 
single,  in  conformity  with  the  single  character  of  the  organ  it  supplies; 
but  in  one  very  rare  Bivalve  Mollusk,  the  foot  is  double,  and  the 
pedal  ganglion  is  double  also.  Third,  the  respiratory  ganglion,  c, 
which  frequently  presents  a  form  that  indicates  a  partial  division  into 
two  halves,  corresponding  with  the  repetition  of  the  organs  it  supplies 
on  the  two  sides  of  the  body.  Besides  these  principal  centres,  we 
meet  with  numerous  smaller  ones  upon  the  nervous  cords,  (/,/,  and 


« 


NERVOUS  SYSTEM  OF  MOLLUSCA.  485 

gi  gt)  which  proceed  from  them  to  the  different  parts  of  the  general 
muscular  envelop  or  mantle. 

853.  Now  it  will  be  observed,  that  the  two  cephalic  ganglia  a,  a, 
are  connected  with  the  pedal  ganglion  6,  by  means  of  a  pair  of  trunks 
proceeding  from  the  former  to  the  latter ;  and  that  they  are,  in  like 
manner,  separately  connected  with  the  respiratory  or  branchial  gan- 
glion, c.  It  is  found,  upon  careful  dissection,  that  these  cords  do  not 
serve  merely  to  bring  the  ganglia  into  relation  ;  but  that  a  part  of 
them  pass  through  the  ganglion  into  the  trunks  proceeding  from  it. 
Thus  of  the  nerves  which  supply  the  large  fleshy  foot,  and  which 
appear  to  proceed  from  the  pedal  ganglion  6,  a  part  are  undoubtedly 
connected  with  that  ganglion  alone,  coming  into  relation  with  its 
vesicular  substance  ;  but  a  part  also  pass  on  to  the  cephalic  ganglia, 
by  the  connecting  trunks, — so  that  these,  rather  than  the  pedal  gan- 
glion, constitute  their  centre.  The  same  may  be  said  of  the  nerves 
proceeding  from  the  branchial  ganglion:  a  portion  of  them  having 
their  centre  in  the  vesicular  matter  of  that  ganglion  ;  whilst  another 
portion  has  no  relation  to  it  whatever  (beyond  that  of  proximity),  but 
passes  through  or  over  it,  to  become  connected  with  the  cephalic 
ganglia.  There  is  good  reason  to  believe,  that  the  pedal  and  branchial 
ganglia  minister  to  the  purely  reflex  actions  of  the  organs  they  re- 
spectively supply  ;  and  that  they  would  serve  this  purpose  as  well,  if 
altogether  cut  off  from  connection  with  the  cephalic  ganglia :  whilst 
the  latter,  being  the  instruments  of  the  actions  which  are  called  forth 
by  sensation  (whether  these  be  of  a  consensual  or  of  a  voluntary  na- 
ture), exert  a  general  control  and  direction  over  the  movements  of  the 
animal. 

854.  It  is  difficult  to  make  satisfactory  experiments  upon  this  sub- 
ject in  these  animals  ;  their  movements  being  for  the  most  part  slow 
and  feeble,  and  their  nervous  system  not  readily  accessible  ;  and  our 
idea  of  the  respective  functions  of  their  ganglia  is  chiefly  founded 
upon  the  distribution  of  their  nerves,  and  upon  the  analogous  opera- 
tions of  the  ganglia  that  correspond  to  them  in  other  animals.  In 
ascending  through  the  series  of  the  Mollusca,  we  find  the  Nervous  sys- 
tem increasing  in  complexity,  in  accordance  with  the  general  organi- 
zation of  the  body:  the  addition  of  new  organs  of  special  sensation, 
and  of  new  parts  to  be  moved  by  muscles,  involving  the  addition  of 
new  ganglionic  centres,  whose  functions  are  especially  adapted  to 
these  purposes.  But  we  find  no  other  multiplication  of  similar  cen- 
tres, than  a  doubling  on  the  two  sides  of  the  body ;  excepting  in  a 
few  cases,  where  the  organs  they  supply  are  correspondingly  multi- 
plied. We  have  a  very  characteristic  example  of  this  in  the  arms  of 
the  Cuttle-fish,  which  are  furnished  with  great  numbers  of  contractile 
suckers,  every  one  possessing  a  ganglion  of  its  own.  Here  we  can 
trace  very  clearly  the  distinction  between  the  reflex  actions  of  each 
individual  sucker,  depending  upon  the  powders  of  its  own  ganglion ; 
and  the  consensual  or  voluntary  movement,  which  results  from  its 
connection  with  the  cephalic  ganglia.     The  nervous  trunk,  which 


486  NERVOUS  SYSTEM  OF  MOLLUSCA. 

proceeds  to  each  arm,  may  be  distinctly  divided  into  two  tracts;  in 
one  of  which  there  is  nothing  but  fibrous  structure,  forming  a  direct 
communication  between  the  suckers  and  the  cephalic  ganglia ;  whilst 
in  the  other  are  contained  the  ganglia,  which  peculiarly  appertain  to 
the  suckers,  and  which  are  connected  with  them  by  distinct  filaments: 
so  that  each  sucker  has  a  separate  relation  with  a  ganglion  of  its  own, 
whilst  all  are  alike  connected  with  the  cephalic  ganglia,  and  are 
placed  under  their  control.  We  see  the  results  of  this  arrangement, 
in  the  modes  in  which  the  contractile  power  of  the  suckers  may  be 
called  into  operation.  When  the  animal  embraces  any  substance 
with  its  arm  (being  directed  to  this  action  by  its  sight  or  other  sensa- 
tion) it  can  bring  all  the  suckers  simultaneously  to  bear  upon  it ;  evi- 
dently by  a  voluntary  or  instinctive  impulse,  transmitted  along  the 
motor  cords,  that  proceed  from  the  cephalic  ganglia  to  the  suckers. 
On  the  other  hand,  any  individual  sucker  may  be  made  to  contract 
and  attach  itself,  by  placing  a  substance  in  contact  with  it  alone ;  and 
this  action  will  take  place  equally  well,  when  the  arm  is  separated 
from  the  body,  or  even  in  a  small  piece  of  the  arm  when  recently 
severed  from  the  rest, — thus  proving  that,  when  it  is  directly  excited 
by  an  impression  made  upon  itself,  it  is  a  reflex  act,  quite  independ- 
ent of  the  cephalic  ganglia,  not  involving  sensation,  and  taking  place 
through  the  medium  of  its  own  ganglion  alone. 

855.  In  the  Molluscous  classes,  generally  speaking,  the  Nervous 
system  bears  but  a  small  proportion  to  the  whole  mass  of  the  body; 
and  the  part  of  it  which  ministers  to  the  general  movements  of  the 
fabric,  is  often  small  in  proportion  to  those  which  serve  some  special 
purpose,  such  as  the  actions  of  respiration.  This  is  what  we  should 
expect  from  the  general  inertness  of  their  character,  and  from  the  small 
amount  of  muscular  structure  which  they  possess.  On  the  other 
hand,  in  the  Articulated  classes,  in  which  the  locomotive  apparatus 
is  highly  developed,  and  its  actions  of  the  most  energetic  kind,  we 
find  the  Nervous  system  almost  entirely  subservient  to  this  function. 
In  its  usual  form,  it  consists  of  a  chain  of  ganglia,  connected  by  a 
double  cord  ;  commencing  in  the  head,  and  passing  backwards  through 
the  body  (Plate  II.,  Fig  2).  The  ganglia,  though  they  usually  appear 
single,  are  really  double  ;  being  composed  of  two  equal  halves,  some- 
times closely  united  on  the  median  line,  but  occasionally  remaining 
separate,  like  the  cephalic  ganglia  of  the  Solen  (Fig.  1,  a,  a),  and 
being  united  together  by  a  transverse  commissural  trunk.  In  like 
manner,  the  longitudinal  cord,  though  really  double  (as  seen  in  the 
upper  part  of  Fig.  2),  often  appears  to  be  single,  in  consequence  of 
the  close  approximation  of  its  lateral  halves  (as  in  the  lower  part  of 
Fig.  2).  In  general  we  find  a  ganglion  in  each  segment;  giving  off 
nerves  to  the  muscles  of  the  legs,  as  in  Insects,  Centipedes,  &c.  ;  or 
to  the  muscles  that  move  the  rings  of  the  body,  where  no  extremities 
are  developed,  as  in  the  leech,  worm,  &c.  In  the  lower  Vermiform 
(or  worm-like)  tribes,  especially  in  the  marine  species,  the  number  of 
segments  is  frequently  very  great,  amounting  even  to  several  hundreds; 


r 


NERVOUS  SYSTEM  OF  ARTICULATA.  487 


and  the  number  of  ganglia  follows  the  same  proportion.  Whatever 
be  their  degree  of  multiplication,  they  seem  but  repetitions  of  one 
another ;  the  functions  of  each  segment  being  the  same  with  those  of 
the  rest.  The  cephalic  ganglia,  however,  are  always  larger  and  more 
important;  they  are  connected  with  the  organs  of  special  sense;  and 
they  evidently  possess  a  power  of  directing  and  controlling  the  move- 
ments of  the  entire  body ;  whilst  the  power  of  each  ganglion  of  the 
trunk  is  confined  to  its  own  segment. — The  longitudinal  ganglionic 
cord  of  Articulata  occupies  a  position,  which  seems  at  first  sight 
altogether  different  from  that  of  the  nervous  system  of  Vertebrated 
animals ;  being  found  in  the  neighbourhood  of  the  ventral  or  inferior 
surface  of  their  bodies;  instead  of  lying  just  beneath  their  dorsal  or 
upper  surface.  There  is  reason,  however,  for  regarding  the  whole 
of  the  body  of  these  animals  as  having  an  inverted  position  ;  so  that 
they  maybe  considered  as  really  crawling  upon  their  backs.  On  this 
view,  their  longitudinal  nervous  tract  corresponds  with  the  spinal  cord 
of .  Vertebrata  in  position^  as  we  shall  find  that  it  does  m  function. 

856.  We  shall  draw  our  chief  illustrations  of  the  structure  of  the 
nervous  system  in  the  Articulated  series,  from  the  class  of  Insects;  in 
which  it  has  been  particularly  examined.  In  these  animals,  the  num- 
ber of  segments  never  exceeds  twelve  (exclusive  of  the  head),  either 
in  their  larva,  pupa,  or  imago  states  ;  and  the  total  number  of  pairs  of 
ganglia,  therefore,  never  exceeds  thirteen,  including  the  cephalic 
ganglia.  These,  in  the  larva,  are  nearly  equal  in  size,  one  to  another 
(Plate  II.,  Fig.  2,  a,  and  1 — 12);  the  functions  of  the  different  seg- 
ments of  the  body  being  almost  uniform ;  and  the  development  of  the 
organs  of  special  sense  not  being  such,  as  to  involve  any  considerable 
predominance  in  the  size  of  the  cephalic  ganglia.  We  observe,  at 
the  anterior  extremity,  the  pair  of  cephalic  ganglia  {a) ;  from  w^hich 
proceeds,  on  each  side,  a  cord  of  communication  to  the  first  ganglion 
(1)  of  the  trunk.  This  double  cord,  with  the  ganglia  above  and  below, 
thus  forms  a  ring,  which  embraces  the  oesophagus ;  the  cephalic  ganglia 
being  situated  on  the  upper  side  of  it,  whilst  the  ganglionic  column  of 
the  trunk  lies  beneath  the  alimentary  canal  along  its  whole  length. 
In  the  Sphinx  ligustri,  or  Privit  Hawk-moth,  the  nervous  system  of 
whose  larva  is  here  represented,  the  last  two  segments  of  the  body  are 
drawn  together,  as  it  were,  into  one;  and  instead  of  distinct  11th  and 
12th  ganglia,  we  find  but  a  single  mass,  nearly  double  the  size  of  the 
rest,  and  obviously  formed  of  the  elements  that  would  have  otherwise 
gone  to  form  the  two. 

857.  When  the  structure  of  the  chain  of  ganglia  is  more  particularly 
inquired  into,  it  is  found  to  consist  of  two  distinct  tracts;  one  of 
which  is  composed  of  nervous  fibres  only,  and  passes  backwards  from 
the  cephalic  ganglia,  over  the  surface  of  all  the  ganglia  of  the  trunk, 
giving  off  branches  to  the  nerves  that  proceed  from  them ;  whilst  the 
other  includes  the  ganglia  themselves.  Hence,  as  in  the  Mollusca, 
every  part  of  the  body  has  two  sets  of  nervous  connections  ;  one  with 
the  cephalic  ganglia;  and  the  other  with  the  ganglion  of  its  own  seg- 


488 


REFLEX  ACTIONS  OF  ARTICULATA. 


Fig.  141. 


Portion  of  the  ganglionic  tract  of  Poly- 
desmus  maculatus j—b,  inter-gangl ionic 
cord;  c,  anterior  nerves;  d,  posterior 
nerves  ;  /,  k,  fibres  of  reflex  action  ;  g,  k, 
•commissural  fibres;  i,  longitudinal  fibres, 
softened  and  enlarged,  as  they  pass 
through  ganglionic  matter. 


merit.  Impressions  made  upon  the  afferent  fibres,  which  proceed 
from  any  part  of  the  body  to  the  cephalic  ganglia,  become  sensations 
when  conveyed  to  the  latter ;  whilst,  in  respondence  to  these,  the 
influence  of  the  instincts,  or  of  the  willj  operating  through  the  cephalic 

ganglia,  harmonizes  and  directs  the 
general  movements  of  the  body,  by 
means  of  the  efferent  nerves  proceeding 
from  them.  For  the  reflex  operations, 
on  the  other  hand,  the  ganglia  of  the 
ventral  cord  are  sufficient;  each  one 
ministering  to  the  actions  of  its  own 
segment,  and,  to  a  certain  extent  also, 
to  those  of  other  segments.  It  has  been 
ascertained  by  the  careful  dissections 
of  Mr.  Newport,  that  of  the  fibres  con- 
stituting the  roots,  by  which  the  nerves 
are  implanted  in  the  ganglia,  some  pass 
into  the  vesicular  matter  of  the  gan- 
glion, and,  after  coming  into  relation 
with  its  vesicular  substance,  pass  out 
again  on  the  same  side  (Fig.  141, y,  /c); 
whilst  a  second  set,  after  traversing  the 
vesicular  matter,  passes  out  by  the  trunks  proceeding  from  the  oppo- 
site side  of  the  same  ganglion  ;  and  a  third  set  runs  along  the  portion 
of  the  cord  which  connects  the  ganglia  of  different  segments,  and 
enters  the  nervous  trunks  that  issue  from  them,  at  a  distance  of  one 
or  more  ganglia  above  or  below.  Thus  it  appears,  that  an  impression 
conveyed  by  an  afferent  fibre  to  any  ganglion,  may  excite  a  motion 
in  the  muscles  of  the  same  side  of  its  own  segment ;  or  in  those  of  the 
opposite  side  ;  or  in  those  of  segments  at  a  greater  or  less  distance, 
according  to  the  point  at  which  the  efferent  fibres  leave  the  cord. 

858.  The  general  conformation  of  Articulated  animals,  and  the  ar- 
rangement of  the  parts  of  their  nervous  system,  render  them  peculiarly 
favourable  subjects  for  the  study  of  the  reflex  actions  ;  some  of  the 
principal  phenomena  of  which  will  now  be  described.  If  the  head  of  a 
Centipede  be  cut  off,  whilst  it  is  in  motion,  the  body  will  continue  to 
move  onwards  by  the  action  of  the  legs ;  and  the  same  w^ill  take  place 
in  the  separate  parts,  if  the  body  be  divided  into  several  distinct  por- 
tions. After  these  actions  have  come  to  an  end,  they  maybe  excited 
again  by  irritating  any  part  of  the  nervous  centres,  or  the  cut  extre- 
mity of  the  nervous  cord.  The  body  is  moved  forwards  by  the  regu- 
lar and  successive  action  of  the  legs,  as  in  the  natural  state ;  but  its 
movements  are  always  forwards,  never  backwards,  and  are  only  di- 
rected to  one  side,  when  the  forward  movement  is  checked  by  an 
interposed  obstacle.  Hence,  although  they  might  seem  to  indicate 
consciousness  and  a  guiding  will,  they  do  not  so  in  reality  ;  for  they 
are  carried  on,  as  it  were,  mechanically:  and  show  no  direction  of  ob- 
ject, no  avoidance  of  danger.     If  the  body  be  opposed  in  its  progress 


t 


I 


REFLEX  AND  CONSENSUAL  ACTIONS  OF  INSECTS.  489 

by  an  obstacle  of  not  more  than  half  its  own  height,  it  mounts  over 
it,  and  moves  directly  onwards,  as  in  its  natural  state ;  but  if  the  ob- 
stacle be  equal  to  its  own  height,  its  progress  is  arrested,  and  the  cut 
extremity  of  the  body  remains  forced  up  against  the  opposing  sub- 
stance,— the  legs  still  continuing  to  move. — If,  again,  the  nervous  cord 
of  a  Centipede  be  divided  in  the  middle  of  the  trunk,  so  that  the 
hinder  legs  are  cut  off  from  connection  with  the  cephalic  ganglia,  they 
will  continue  to  move,  but  not  in  harmony  with  those  of  the  fore  part 
of  the  body;  being  completely  paralyzed,  as  far  as  the  animal's  con- 
trolling power  is  concerned ;  though  still  capable  of  performing  reflex 
movements,  by  the  influence  of  their  own  ganglia,  which  may  thus 
continue  to  propel  the  body,  in  opposition  to  the  determination  of  the 
animal  itself. — The  case  is  still  more  remarkable,  when  the  nervous 
cord  is  not  merely  divided,  but  a  portion  of  it  is  entirely  removed 
from  the  middle  of  the  trunk ;  for  the  anterior  legs  still  remain  obe- 
dient to  the  animal's  control;  the  legs  of  the  segments,  from  which 
the  nervous  cord  has  been  removed,  are  altogether  motionless;  whilst 
those  of  the  posterior  segments  continue  to  act,  through  the  reflex 
powers  of  their  own  ganglia,  in  a  manner  which  shows  that  the  animal 
has  no  power  of  checking  or  directing  them. 

859.  The  stimulus  to  the  reflex  movements  of  the  legs,  in  the  fore- 
going cases,  appears  to  be  given  by  the  contact  of  the  extremities  with 
the  solid  surface  on  which  they  rest.  In  other  cases,  the  appropriate 
impression  can  only  be  made  by  the  contact  of  liquid ;  thus  a  Dytiscus 
(a  kind  of  water-beetle),  having  had  its  cephalic  gjanglia  removed, 
remained  motionless,  so  long  as  it  rested  upon  a  dry  surface  ;  but  when 
cast  into  w^ater,  it  executed  the  usual  swimming  motions  with  great 
energy  and  rapidity,  striking  all  its  comrades  to  one  side  by  its  vio- 
lence, and  persisting  in  these  for  more  than  half  an  hour.  Other 
movements,  again,  may  be  excited  through  the  respiratory  surface. 
Thus,  if  the  head  of  a  Centipede  be  cut  off,  and  while  it  remains  at 
rest,  some  irritating  vapour  (such  as  that  of  ammonia  or  muriatic 
acid)  be  caused  to  enter  the  air  tubes  on  one  side  of  the  trunk,  the 
body  will  be  immediately  bent  in  the  opposite  direction,  so  as  to 
withdraw  itself  as  much  as  possible  from  the  influence  of  the  vapour ; 
if  the  same  irritation  be  then  applied  on  the  other  side,  the  reverse 
movement  will  take  place ;  and  the  body  may  be  caused  to  bend  in 
two  or  three  different  curves,  by  bringing  the  irritating  vapour  into  the 
neighbourhood  of  different  parts  of  either  side.  This  movement  is 
evidently  a  reflex  one,  and  serves  to  withdraw  the  entrances  of  the  air- 
tubes  from  the  source  of  irritation ;  in  the  same  manner  as  the  acts  of 
coughing  and  sneezing  in  the  higher  animals  cause  the  expulsion,  from 
the  air-passages,  of  solid,  liquid  or  gaseous  irritating  matters,  which 
may  have  found  their  way  into  them. 

860.  From  these  and  similar  facts  it  appears,  that  the  ordinary 
movements  of  the  legs  and  wings  of  Articulated  animals  are  of  a  reflex 
nature,  and  may  be  effected  solely  through  the  ganglia  with  which 
these  organs  are  severally  connected ;  whilst  in  the  perfect  being,  they 


490  CEPHALIC  AND  RESPIRATORY  GANGLIA  OF  INSECTS. 

are  harmonized,  controlled,  and  directed  by  its  instinct  or  its  will, 
which  act  through  the  cephalic  ganglia  and  the  nerves  proceeding 
from  them.  There  is  strong  reason  to  believe,  that  the  operations  to 
which  these  ganglia  are  subservient,  are  almost  entirely  of  a  consensual 
nature ;  being  immediately  prompted  by  sensations,  chiefly  those  of 
sight,  and  seldom  involving  any  processes  of  a  truly  rational  character. 
When  we  attentively  consider  the  habits  of  these  animals,  we  find 
that  their  actions,  though  evidently  directed  to  the  attainment  of  cer- 
tain ends,  are  very  far  from  being  of  the  same  spontaneous  nature,  or 
from  possessing  the  same  designed  adaptation  of  means  to  ends,  as 
those  performed  by  ourselves,  or  by  the  more  intelligent  Vertebrata, 
under  like  circumstances.  We  judge  of  this  by  their  unvarying  cha- 
racter,— the  different  individuals  of  the  same  species  executing  pre- 
cisely the  same  movements,  when  the  circumstances  are  the  same  ;  and 
by  the  very  elaborate  nature  of  the  mental  operations,  which  would  be 
required,  in  many  instances,  to  arrive  at  the  same  results  by  an  effort 
of  reason.  Of  such  we  cannot  have  a  more  remarkable  example,  than 
is  to  be  found  in  the  operations  of  Bees,  Wasps,  and  other  social  In- 
sects; which  construct  habitations  for  themselves,  upon  a  plan  which 
the  most  enlightened  human  intelligence,  working  according  to  the 
most  refined  geometrical  principles,  could  not  surpass;  but  which  yet 
do  so  without  education  communicated  by  their  parents,  or  progressive 
attempts  of  their  own,  and  with  no  trace  of  hesitation,  confusion,  or 
interruption, — the  different  individuals  of  a  community  all  labouring 
effectively  for  one  common  purpose,  because  their  instinctive  or  con- 
sensual impulses  are  the  same. 

861.  It  is  interesting  to  remark  that,  in  the  change  from  the  Larva 
to  the  perfect  or  Imago  state  of  the  Insect,  the  Cephalic  ganglia 
undergo  a  great  increase  in  size.  (Plate  II.,  Fig.  3,  a,  a.)  This 
evidently  has  reference  to  the  increased  development  of  the  organs  of 
special  sense  in  the  latter ;  the  eyes  being  much  more  perfectly  formed ; 
antennae  and  other  appendages  used  for  feeling  being  evolved  ;  and 
rudimentary  organs  of  hearing  and  smell  being  added.  In  respondence 
to  the  new  sensations,  which  the  animal  will  thus  acquire,  a  great 
number  of  new  instinctive  actions  are  manifested  ;  indeed,  it  may  be 
said,  that  the  instincts  of  the  perfect  Insect  have  frequently  nothing 
in  common  with  those  of  the  Larva.  The  latter  have  reference  to  the 
acquirement  of  food ;  the  former  chiefly  relate  to  the  acts  of  reproduc- 
tion, and  to  the  provisions  requisite  for  the  deposit  and  protection  of 
the  eggs  and  the  early  nutrition  of  the  young. — We  find  another  im- 
portant change  in  the  nervous  system  of  the  adult  or  perfect  Insect; 
namely,  the  concentration  of  the  ganglionic  matter  of  the  ventral  cord 
in  the  thoracic  region  {e,f) ;  with  the  three  segments  of  which,  the 
three  pairs  of  legs  and  the  two  pairs  of  wings  are  connected.  The 
nine  segments  of  the  abdomen,  in  the  perfect  Insect,  give  attachment 
to  no  organs  of  motion,  and  are  seldom  themselves  very  movable  ;  and 
we  find  that  the  ganglia  which  correspond  with  them  have  undergone 
no  increase  in  size,  but  have  rather  diminished,  and  have  sometimes 


STOMATO-GASTRIC  AND  OTHER  NERVES  OF  INVERTEBRATA.   491 

almost  completely  disappeared.  Where  the  last  segment,  however, 
is  furnished  with  a  particularly  movable  appendage,  such  as  a  sting, 
or  an  ovipositor,  we  always  find  a  large  ganglion  in  connection 
wdth  it. 

862.  These  ganglia  of  the  ventral  cord  evidently  correspond  in 
function  with  the  pedal  ganglion  of  the  Mollusca ;  being  so  many 
repetitions  of  it ;  in  accordance  with  the  number  of  members.  We 
have  now  to  speak  of  a  system  of  respiratory  ganglia,  which  also  are 
repeated  in  like  manner,  in  accordance  with  the  condition  of  the  respi- 
ratory apparatus ;  this  being  diffused  through  the  whole  body,  in  most 
of  the  Articulata,  instead  of  being  restricted  to  one  spot  as  in  the 
Mollusca.  The  system  of  respiratory  nerves  consists  of  a  chain  of 
minute  ganglia,  lying  upon  the  larger  cord,  and  sending  off  its  delicate 
nerves  between  those  that  proceed  from  the  ganglia  of  the  latter,  as 
seen  in  Fig.  2.  These  respiratory  ganglia  and  their  nerves  are  best 
seen  in  the  thoracic  portion  of  the  cord,  where  the  cords  of  communi- 
cation between  the  pedal  ganglia  diverge  or  separate  from  one  another. 
And  this  is  particularly  the  case  in  the  Pupa  state,  when  the  whole 
cord  is  being  shortened,  and  their  divergence  is  increased.  The 
thoracic  portion  of  the  cord,  in  the  Pupa  of  the  Sphinx  ligustri,  is 
shown  in  Plate  II.,  Fig.  4;  where  a,  &,  and  c,  represent  the  2d,  3d, 
and  4th  double  ganglia  of  the  ventral  cord  ;  c?,  c?,  the  cords  of  connec- 
tion between  them,  here  widely  diverging  laterally ;  and  e,  e,  the  small 
respiratory  ganglia,  which  are  connected  with  each  other  by  delicate 
filaments  that  pass  over  the  ganglia  of  the  ventral  cord,  and  which 
send  off  lateral  branches,  that  are  distributed  to  the  air-tubes  and 
other  parts  of  the  respiratory  apparatus,  and  communicate  with  those 
of  the  other  system. 

863.  Besides  the  Respiratory  system  of  ganglia  and  nerves,  there 
is  in  Insects,  as  in  some  Mollusks,  a  set  of  minute  ganglia,  which  is 
especially  connected  with  the  acts  of  mastication  and  swallowing,  its 
filaments  being  distributed  to  the  muscles  of  the  mouth  and  pharynx, 
and  some  of  its  ganglia  being  even  found  on  the  stomach,  where 
that  organ  is  remarkable  for  its  muscular  powers.  The  number  and 
arrangement  of  these  ganglia  vary  considerably  in  different  animals, 
even  in  those  of  the  same  group ;  but  some  traces  of  this  distinct 
system,  which  is  designated  as  the  stomato-gastric,  may  always  be 
found.  One  of  the  minute  ganglia  appertaining  to  it,  and  forming  its 
anterior  termination,  is  seen  to  lie  on  the  median  line,  in  front  of  the 
great  cephalic  ganglia,  in  Plate  II.,  Fig.  3,  c.  From  this  a  trunk 
passes  backwards  along  the  oesophagus ;  which  may  be  likened  to  the 
oesophageal  branches  of  the  Par  vagum  in  Vertebrata.  Two  other 
small  ganglia,  communicating  with  this,  are  seen  at  d,  d. 

864.  We  are  not  without  traces,  moreover,  among  Invertebrated 
animals,  of  the  Sympathetic  system  of  the  higher  classes ;  though  it  is 
quite  a  mistake  to  compare  the  entire  system  of  nerves  and  ganglia  in 
the  former,  with  the  Sympathetic  system  of  the  latter, — as  was  for- 
merly done.     The  chief  distribution  of  the  branches  of  the  Sympa- 


492  NERVOUS  SYSTEM  OF  VERTEBRATA. 

thetic  of  Vertebrata  is  upon  the  walls  of  the  blood-vessels,  and  upon 
the  muscular  substance  of  the  heart  and  alimentary  canal;  and  it  is  by 
the  passage  of  some  of  the  filaments,  from  the  system  of  minute 
ganglia  just  pointed  out,  to  the  dorsal  vessel,  that  we  recognize  it  as 
combining  the  functions  of  the  Sympathetic  with  those  of  the  gastric 
and  cardiac  portions  of  the  Par  vagum.  It  will  be  remembered  that 
there  is  a  frequent  inosculation  between  these  two  nerves,  even  in  the 
highest  animals. 

865.  Thus  we  have  seen  that,  in  Invertebrated  animals,  the  Nervous 
System  consists  of  a  series  of  isolated  ganglia,  connected  together  by 
fibrous  trunks.  The  number  of  these  ganglia,  and  the  variety  of  their 
function,  entirely  depend  upon  the  number  and  variety  of  the  organs 
to  be  supplied.  In  the  lowest  Mollusca,  the  regulation  of  the  ingress 
and  egress  of  water  seems  almost  the  only  function  to  be  performed ; 
and  here  we  have  but  a  single  ganglion.  In  the  Star-fish,  we  have 
five  or  more  ganglia  ;  but  they  are  all  repetitions,  one  of  another.  In 
the  higher  Mollusca,  and  in  Articulata,  we  have  a  ganglion,  or  more 
commonly  a  pair  of  ganglia,  situated  at  the  anterior  extremity  of  the 
body,  connected  with  the  organs  of  special  sensation,  and  evidently 
exerting  a  dominant  influence  over  the  rest.  In  the  lower  Mollusca, 
we  have  but  a  single  ganglion  for  general  locomotion ;  but  this  is 
doubled  laterally,  and  repeated  longitudinally  in  the  Articulata,  in 
accordance  with  the  multiplication  of  their  locomotive  organs,  so  as  to 
form  the  ventral  cord.  In  like  manner,  the  Mollusca  possess  a  single 
ganglionic  centre  for  the  respiratory  movements;  and  this  is  repeated 
in  every  segment  of  the  Articulata,  forming  a  chain  of  respiratory 
ganglia,  which  regulates  the  actions  of  the  extensively-diffused  respi- 
ratory apparatus  of  these  animals.  The  acts  of  mastication  and  deglu- 
tition, again,  in  both  sub-kingdoms,  are  under  the  control  of  a  distinct 
set  of  ganglionic  centres ;  which  are  connected,  however,  like  the 
preceding,  with  the  cephalic  ganglia ;  and  it  is  probable  that,  as  in 
other  cases,  some  filaments  from  the  latter  enter  into  all  the  branches, 
which  they  transmit  to  the  muscles.  And  we  have  further  seen,  that, 
wherever  special  organs  are  developed,  whose  operations  depend 
upon  muscular  contraction,  ganglionic  centres  are  developed  in 
immediate  relation  with  them  ;  so  as  to  enable  them  to  act  by  their 
simple  reflex  power,  as  well  as  under  the  direction  of  the  cephalic 
ganglia ; — as  in  the  case  of  the  suckers  of  the  Cuttle-fish. 

866.  When  we  direct  our  attention  to  the  Nervous  system  of  the 
Vertebrated  series,  we  perceive  that  it  diflfers  from  that  of  the  Inver- 
tebrated classes  we  have  been  considering  in  two  remarkable  fea- 
tures. In  these  last,  it  has  seemed  but  as  a  mere  appendage  to  the 
rest  of  the  system,  designed  to  bring  its  several  parts  into  more  advan- 
tageous relation.  On  the  other  hand,  in  the  Vertebrata,  the  whole 
structure  appears  subservient  to  it,  and  designed  but  to  carry  its  pur- 
poses into  operation.  Again,  in  the  Invertebrata,  we  do  not  find  any 
special  adaptation  of  the  organs  of  support  for  the  protection  of  the 
Nervous  System.     It  is  either  enclosed,  with  the  other  soft  parts  of 


I 


NERVOUS  SYSTEM  OF  VERTEBRATA.  493 

the  body,  in  one  general  hard  tegument,  as  in  the  Star-fish  and  other 
Echinodermata,  and  in  Insects,  Crustacea,  and  other  Articulata ;  or 
it  receives  a  still  more  imperfect  protection,  or  even  none  at  all,  as 
in  the  Mollusca.  Now  in  the  Vertebrata,  we  find  a  special  and  com- 
plex bony  apparatus,  adapted  in  the  most  perfect  manner  for  the  pro- 
tection of  the  Nervous  system ;  and  it  is,  in  fact,  the  possession  of  a 
jointed  spinal  column,  and  of  its  cranial  expansion,  which  best  cha- 
racterizes the  group. 

867.  The  Nervous  System  of  Vertebrata  is  not  merely  remarkable 
for  its  high  development,  relatively  to  the  remainder  of  the  structure. 
It  is  also  distinguished  by  the  possession  of  parts,  to  which  we  have 
nothing  analogous  in  the  lower  tribes ;  and  by  the  mode  in  which 
these  are  concentrated  and  combined,  so  as  to  form  one  continuous 
mass,  instead  of  consisting  of  a  series  of  scattered  ganglia. — The 
chief  parts  which  are  newly  introduced  (so  to  speak)  in  this  sub- 
kingdom,  are  the  Cerebral  Hemispheres  and  Cerebellum ;  of  which 
there  are  no  traces  whatever  in  the  lower  Articulata  and  Mollusca, 
and  but  very  minute  representations  in  the  highest.  These  are  super- 
imposed, as  it  were,  upon  the  cephalic  ganglia  connected  with  the 
organs  of  special  sense,  and  upon  the  cords  that  connect  them  with 
the  first  ganglion  of  the  trunk. — Again  we  find  that  the  locomotive 
ganglia,  which  formed  the  long-knotted  cord  of  the  Articulata,  are 
united  with  the  centres  of  the  respiratory  system,  and  with  those  of 
the  stomato-gastric  system ;  to  form  one  continuous  tract,  which  com- 
mences anteriorly  from  the  ganglia  of  special  sense,  and  runs  back- 
wards* without  interruption,  in  the  canal  of  the  Vertebral  column, 
forming  the  Spinal  Cord.  This  is  a  continuous  instead  of  an  inter- 
rupted ganglionic  mass ;  it  is  composed  of  two  lateral  halves,  precisely 
similar  to  each  other;  and  each  of  these  consists  of  two  parts,  as  dis- 
tinct from  each  other  as  the  two  tracts  in  the  ventral  cord  of  the  Arti- 
culata,— namely,  a  fibrous  structure,  which  is  continuous  between  the 
Encephalon  (or  collection  of  nervous  masses  within  the  cranium)  and 
certain  fibres  of  the  roots  of  the  spinal  nerves,  and  which  also  serves 
to  connect  together  the  diflferent  parts  of  the  cord  itself, — and  a  vesi- 
cular portion,  which  forms  the  proper  centre  of  another  set  of  fibres 
entering  into  the  roots  of  those  nerves.  The  anterior  portion  of  the 
Spinal  cord,  which  is  prolonged  into  the  cranium,  and  comes  into 
immediate  relation  with  the  encephalon,  is  termed  the  Medulla  Ob- 
longata. It  is  in  this  that  the  centres  of  the  respiratory  and  stomato- 
gastric  nerves  are  found  ;  the  situation  of  these  important  ganglia 
within  the  cranium,  being  obviously  destined  to  protect  them  from 
those  injuries  to  which  the  Spinal  Cord  itself  is  liable. 

868.  Thus,  then,  we  recognize  in  the  Nervous  system  of  Vertebrata 
the  following  fundamental  parts. — 1.  A  system  of  ganglia  subservient 
to  the  reflex  actions  of  the  organs  of  locomotion,  and  corresponding 

*  When  we  speak  of  the  Vertebrata  generally,  their  bodies  are  of  course  supposed 
to  be  in  a  horizontal  position, — not  vertical  as  in  Man. 


494  NERVOUS  CENTRES  OF  FISHES. 

with  the  chain  of  pedal  or  locomotive  ganglia  that  makes  up  the  chief 
part  of  the  ventral  cord  of  the  Articulata ;  in  this  system,  the  gray  or 
vesicular  matter  forms  one  continuous  tract,  which  occupies  the  inte- 
rior of  the  Spinal  Cord. — 2.  A  ganglionic  centre  for  the  movements 
of  respiration^  and  another  for  those  of  mastication  and  deglutition; 
these,  with  part  of  the  preceding,  make  up  the  proper  substance  of 
the  Medulla  Oblongata. — 3.  A  series  of  ganglia,  in  immediate  con- 
nection with  the  organs  of  ♦§)eaflZ  Sense;  these  are  situated  within  the 
cranium,  at  the  anterior  extremity  of  the  Medulla  Oblongata;  and,  in 
the  lowest  Vertebrata,  they  constitute  by  far  the  largest  portion  of  the 
entire  Encephalon. — 4.  The  Cerebellum,  which  is  a  sort  of  off- shot 
from  the  upper  extremity  of  the  Medulla  Oblongata,  lying  behind  the 
preceding. — 5.  The  Cerebral  Hemispheres,  a  pair  of  ganglionic  masses, 
which  lie  upon  the  ganglia  of  special  sense,  capping  them  over  more 
or  less  completely,  according  to  their  relative  development. — These 
two  last  organs  exist  in  the  lowest  Vertebrata,  as  in  Invertebrated 
animals  generally,  in  quite  a  rudimentary  state ;  but  their  develop- 
ment, relatively  to  other  parts  of  the  Encephalon,  and  to  the  entire 
bulk  of  the  animal,  increases  as  we  ascend  the  scale ;  so  that  in  Man 
and  the  higher  Mammalia  they  constitute  by  far  the  largest  portion  of 
the  Nervous  centres,  and  are  essential  to  the  greater  part  of  the  ope- 
rations of  the  Nervous  system.  The  development  of  the  Cerebral 
Hemispheres  holds  a  close  relation  with  the  increase  of  the  Intelli- 
gence, and  with  the  predominance  of  the  Will  over  the  involuntary 
impulses.  The  increased  size  of  the  Cerebellum,  on  the  other  hand, 
seems  connected  with  the  necessity  which  exists,  for  the  adjustment 
and  combination  of  the  locomotive  powers,  when  the  variety  in  the 
movements  performed  by  the  animal  is  great,  and  a  more  perfect 
harmony  is  required  among  them. — A  sketch  of  the  mode  in  which 
these  different  parts  are  combined  and  arranged  in  the  several 
classes  of  Vertebrata,  and  of  their  relative  development  in  each, 
will  aid  us  in  the  subsequent  more  detailed  examination  of  their 
functions. 

869.  In  the  class  of  Fishes,  taken  as  a  whole,  the  Encephalon  bears 
a  much  smaller  proportion  to  the  Spinal  Cord,  than  in  the  higher 
Vertebrata.  In  the  curious  Amphioxus,  or  Lancelot,  there  is  no  dis- 
coverable nervous  mass  anterior  to  the  Medulla  Oblongata ;  and  we 
have  here,  therefore,  an  animal  regularly  formed  upon  the  plan,  which 
occasionally  presents  itself  as  a  monstrosity  in  Man,  namely,  having 
the  Spinal  Cord  and  Medulla  Oblongata  for  the  whole  of  the  nervous 
centres,  and  being  anencephalous,  or  destitute  of  any  proper  ence- 
phalon. In  some  of  the  lowest  Vermiform  (worm-like)  Fishes,  such 
as  the  Lamprey,  the  cephalic  masses  are  very  little  more  developed 
in  proportion  to  the  Spinal  Cord,  than  are  the  cephalic  ganglia  of 
Insects  in  reference  to  their  chain  of  ventral  ganglia.  But  as  the 
organs  of  special  sense  acquire  a  more  complete  evolution,  we  find 
the  ganglia  connected  with  them  presenting  a  greatly-increased  size. 
On  opening  the  cranial  cavity  of  a  Fish,  we  usually  observe  four 


ENCEPHALON  OF  FISHES  AND  OF  HUMAN  EMBRYO.  495 

nervous  masses  (three  of  them  in  pairs)  lying,  one  in  front  of  the 
other,  nearly  in  the  same  line  with  the  Spinal  cord.  The  first  or  most 
anterior  of  these  are  the  Olfactory  ganglia  (Plate  II.,  Figs.  5,  6,  7,  a), 
or  the  ganglia  of  the  nerves  of  smell ;  the  nature  of  which  is  known, 
from  their  being  situated  at  the  origin  of  the  Olfactory  nerves.  In  the 
Shark  and  some  other  Fishes,  these  are  separated  from  the  rest  by 
peduncles  or  foot-stalks ;  a  fact  of  much  interest,  as  explaining  the 
arrangement  which  we  find  in  Man.  What  is  commonly  termed  the 
trunk  of  his  Olfactive  nerve  is  really  the  commissure  connecting  the 
Qlfactive  ganglion, — known  as  the  bulbous  enlargement  that  lies 
upon  the  cribriform  plate  of  the  Ethmoid  bone, — with  the  other  por- 
tions of  his  Encephalon  ;  the  proper  fibres  of  the  nerve  being  those, 
which  come  off  from  this  ganglion,  in  the  numerous  branches  that 
proceed  from  it  into  the  nasal  cavity. — Behind  the  Olfactive  ganglia 
is  a  pair  of  masses,  6,  6,  of  which  the  relative  size  varies  greatly  in 
different  Fishes.  Thus  in  the  Perch,  whose  Encephalon  is  here 
figured,  their  size  is  intermediate  between  that  of  the  first  and  third 
pairs;  being  as  much  inferior  to  that  of  the  third,  as  it  is  superior  to 
that  of  the  first.  On  the  other  hand,  in  the  Shark  and  several  other 
Fishes,  they  are  considerably  larger  than  the  succeeding  pair.  These 
second  ganglia  are  the  Cerebral  Hemispheres. — Behind  them,  and 
forming  the  third  pair  of  ganglionic  masses,  c,  c,  are  two  large  bodies, 
from  which  the  optic  nerves  arise ;  these  are  evidently  the  Optic 
ganglia,  corresponding  to  the  principal  mass  of  the  cephalic  ganglia 
in  Insects,  and  the  higher  Mollusca. — And  at  the  back  of  these,  over- 
lying the  top  of  the  spinal  cord,  is  a  single  mass,  d^  the  Cerebellum. 
This,  also,  varies  greatly  in  its  relative  dimensions;  being  much  more 
highly  developed  in  the  Active  and  rapacious  Sharks,  than  it  is  in 
Fishes  of  inferior  muscular  energy  and  variety  of  movement. — The 
Spinal  Cord  e,  is  divided  at  the  top  by  a  fissure,  w^hich  is  most  wide 
and  deep  beneath  the  cerebellum,  where  there  is  a  complete  sepa- 
ration between  its  two  halves.  This  opening  corresponds  to  that, 
through  which  the  oesophagus  passes  in  the  Invertebrata ;  but  as  the 
entire  nervous  mass  of  Vertebrated  animals  lies  above  the  alimentary 
canal  (or  nearer  the  dorsal  surface),  it  does  not  serve  the  same  pur- 
pose in  them ;  and  in  the  higher  classes,  the  fissure  is  almost  entirely 
closed  by  the  union  of  the  two  halves  on  the  median  plane, — the 
fourth  ventricle,  however,  being  a  remnant  of  it.  This  cavity  is 
partly  seen  in  Fig.  7,  which  is  a  vertical  section  of  the  brain  whose 
upper  and  under  surfaces  are  shown  in  Figs.  5  and  6. 

870.  The  Optic  lobes  of  Fishes  must  not  be  confounded  with  the 
Thalami  optici  of  the  higher  Vertebrata,  with  which  they  have  only  a 
slight  analogy,  as  is  proved  by  their  position  and  connections.  They 
are  rather  to  be  compared  with  the  Corpora  Quadrigemina,  which  are 
the  real  ganglia  of  the  optic  nerve.  Their  analogy  is  not  so  complete, 
however,  to  these  bodies  in  their  fully-formed  brain  of  the  higher 
Vertebrata ;  as  to  the  certain  parts  which  occupy  their  place  at  an 
earlier  period.     In  the  Human  embryo,  at  about  the  6th  week,  the 


496  NERVOUS  SYSTEM  OF  FISHES  AND  REPTILES. 

Encephalon  consists  of  a  series  of  vesicles  arranged  in  a  line  with 
each  other;  of  which  those  that  represent  the  cerebrum  (6,  Fig.  14^) 
are  the  smallest,  whilst  that  which  represents  the  cerebellum  {d)  is 
the  largest.     Between  the  cerebral  and  cerebellic  vesicles,  are  two 

others,  (c,  and  a),  of  which  the  pos- 
terior one  is  the  Optic  ganglion,  and 
answers  to  the  Tubercula  quadrige- 
mina  ;  whilst  the  anterior  contains 
the  third  ventricle,  and  corresponds 
in  some  degree  to  the  thalami  optici. 
This  condition  is  precisely  represent- 
ed in  the  Lamprey ;  but  in  most 
Fishes,  the  Optic  ganglia,  and  the 
parts  surrounding  the  third  ventricle, 
form  but  one  lobe  ;  so  that  the  third 
ventricle  seems  hollowed  out  of  the 
optic  ganglia,  as  shown  in  Fig.  7,  c 
(Plate  II.).— Besides  the  Olfactive 
Human  embryo  of  sixth  week,  enlarged     and  Ontip  cranD-lia   there  are  in  manv 

about  three    time8:-a,  vesicle  of  corpSra  ^V  ,  ^P"^_  gf  "g'^'^J  ^"*^I ^^  '^^^  "^  "»^."J 

quadrigemina;  6,  vesicle  of  cerebral  hemi-  FlshcS      dlstinCt      Audltory      ganglia, 

spheres;  c.  vesicle  of  ihalami  optici  and  third  ^  i  •    i     .1  ^i      <        •     •    i. 

ventricle;  ««,  vesicle  for  cerebellum  and  me-  irom  WhlCh  thC    nCrVCS    that  minister 

dullaoblongaia;e,  auditory  vesicle;/,  olfac-  .        .v         c«:.ncp      c\f    ViPnrino-    nrimnnfp  • 

tory  fossa;  A,  liver;  **  caudal  extremity.  tO    the     SenSC     01     Hearing    OriginaiC  , 

these  are  frequently  blended,  how- 
ever, with  the  Medulla  oblongata,  their  vesicular  substance  forming 
a  part  of  its  gray  matter. — It  is  curious  to  notice  the  very  large  com- 
parative size  of  the  Pineal  gland  (/*),  and  of  the  Pituitary  body  (A), 
in  this  class ;  the  functions  of  these  organs  are  entirely  unknown. 

871.  The  Encephalon  oi  Reptiles  does  not  show  any  considerable 
advance  in  its  general  structure,  above  that  of  the  higher  Fishes.  The 
Cerebral  Hemispheres  (Figs.  8,  9,  10,  h)  are  always  much  larger  than 
the  Olfactive  and  Optic  ganglia  ;  and  they  generally  cover  in  the 
latter  (c,  e)  in  part,  by  their  posterior  extremities.  The  Cerebellum  is 
almost  invariably  of  small  proportional  dimensions ;  and  this  is  espe- 
cially the  case  in  the  Frog,  in  which  it  does  not  even  cover  in  the 
fourth  ventricle.  This  low  development  of  the  Cerebellum  in  Rep- 
tiles, is  what  might  be  anticipated  from  the  general  inertness  of  these 
animals,  and  the  want  of  variety  in  their  movements.  The  Spinal 
Cord  is  still  very  large,  in  proportion  to  the  nervous  masses  contained 
in  the  skull ;  and,  as  we  shall  hereafter  see,  its  power  of  keeping  up 
the  movements  of  the  body,  after  it  has  been  cut  off  from  all  connec- 
tion with  the  brain,  is  very  considerable. — We  find  that,  in  Reptiles, 
as  in  Fishes,  the  Spinal  Cord  may  have  a  nearly  uniform  size  from 
one  extremity  to  the  other,  like  the  ventral  cord  of  the  lower  Articu- 
lata  ;  or  it  may  present  considerable  enlargements  at  particular  spots, 
like  the  ganglionic  cord  in  the  thoracic  region  of  Insects.  This  dif- 
ference depends  upon  the  degree  of  development  of  the  special  loco- 
motive organs.  Thus  in  the  Eel  and  Serpent,  whose  movements  are 
accomplished  by  the  undulations  of  the  entire  trunk,  and  which  are 


NERVOUS  CENTRES  OF  BIRDS  AND  MAMMALS.  497 

destitute  of  members,  we  find  an  uniform  development  of  ganglionic 
matter  in  the  spinal  cord.  On  the  other  hand,  in  the  Flying-fish,  in 
which  the  pectoral  fins  or  anterior  extremities  effect  the  greater  part 
of  the  propulsion  of  the  body,  we  find  a  great  ganglionic  enlargement 
of  the  Spinal  cord,  at  the  part  with  which  the  nerves  of  those  mem- 
bers are  connected :  in  the  Frog,  whose  movements  are  chiefly 
effected  by  the  posterior  extremities,  we  find  a  similar  enlargement  at 
the  roots  of  the  crural  nerves ;  and  in  the  Turtles  and  Lizards,  the 
two  pairs  of  whose  members  are  nearly  equal  in  function,  and  serve 
to  effect  the  principal  movements  of  the  body,  we  find  an  anterior  and 
posterior  enlargement  of  the  Spinal  Cord,  corresponding  to  the  parts 
with  which  the  nerves  of  these  members  are  connected. 

872.  We  find  in  Birds  a  considerable  advance  in  the  character  of 
the  Encephalon,  towards  that  which  it  presents  in  Mammalia.  The 
Cerebral  Hemispheres  (Plate  II.,  Figs.  11,  12,  13,  b)  are  greatly  in- 
creased in  size  ;  and  then  cover  in,  not  merely  the  olfactory  ganglia, 
but  in  great  part  also  the  optic  ganglia.     The  former  are  of  compara- 

ttively  small  size  ;  the  organ  of  smell  in  Birds  not  being  much  deve- 
loped. The  latter  are  very  large,  in  conformity  with  the  acuteness 
of  sight,  which  is  highly  characteristic  of  the  class.  The  Cerebellum 
is  of  large  size,  as  we  should  expect  from  the  number  and  complexity 
of  the  muscular  movements  performed  by  animals  of  this  class ;  but 
it  is  still  undivided  into  hemispheres.  The  Spinal  Cord  is  still  of 
considerable  size  in  comparison  with  the  Encephalon  ;  and  it  is  much 
enlarged  at  the  points  whence  the  legs  and  wings  originate.  In  the 
species  which  have  the  most  energetic  flight,  such  as  the  Swallow, 
the  enlargement  is  the  greatest  where  the  nerves  of  the  wings  come 
off;  but  in  those  which,  like  the  Ostrich,  move  principally  by  running 
on  the  ground,  the  posterior  enlargement,  from  which  the  legs  are 
supplied  with  nerves,  is  much  the  more  considerable. 

873.  In  the  Mammalia  we  find  the  size  and  general  development 
of  the  Encephalon  presenting  a  gradual  increase,  as  we  ascend  the 
series,  from  the  non-placental  Monotremes  and  Marsupials,  towards 
Man.  In  the  former,  the  Hemispheres  exhibit  no  convolutions;  and 
the  great  transverse  commissure,  or  connecting  band  of  fibrous  struc- 
ture,— termed  the  corpus  callosum, — is  deficient.  As  we  rise  through 
the  true  viviparous  division  of  the  class,  w^e  notice  a  gradually  in- 
creasing prolongation  of  the  Cerebral  Hemispheres  backwards;  so 
that  first  the  optic  ganglia,  and  then  the  cerebellum,  are  covered  in 
by  them.  The  latter  partly  shows  itself,  however,  in  all  but  Man  and 
the  Quadrumana,  when  we  look  at  the  brain  from  above  downwards ; 
as  we  see  in  the  Encephalon  of  the  Sheep  (Plate  II.,  Figs.  14,  15,  d). 
The  Cerebral  hemispheres  increase,  not  only  in  size,  but  also  in 
complexity  of  structure,  both  external  and  internal.  Their  exterior, 
instead  of  remaining  smooth,  is  marked  by  convolutions  ;  which  serve 
to  extend  very  greatly  the  amount  of  surface,  over  which  blood-ves- 
sels can  pass  into  the  gray  substance.  Their  internal  structure  be- 
comes more  complex,  in  the  same  proportion  as  their  size  and  the 

32 


498  NERVOUS  CENTRES  OF  MAMMALIA.— SPINAL  CORD. 

depth  of  their  convolutions  increase ;  and  in  Man  all  these  conditions 
present  themselves  in  a  far  higher  degree  than  in  any  other  animal. 
The  number  of  commissural  bands,  connecting  the  two  hemispheres 
with  each  other  transversely,  and  uniting  their  anterior  and  posterior 
portions,  is  very  greatly  increased  ;  and,  in  fact,  a  large  proportion  of 
their  mass  is  composed,  in  Man  and  the  higher  Mammalia,  of  fibres 
of  this  character.  In  proportion  to  the  increase  of  the  Cerebral  hemi- 
spheres, there  is  a  diminution  in  the  size  of  the  ganglia  of  special 
sense  ;  and  this  is  seen  when  we  compare  them,  not  merely  with  the 
rest  of  the  Encephalon,  but  even  with  the  Spinal  Cord.  The  Olfac- 
tive  ganglia  (Fig.  14,  a),  are  always  readily  discoverable  ;  being 
separated  from  the  remainder  of  the  encephalic  masses  by  a  peduncle 
on  each  side.  The  Optic  ganglia,  (Fig.  15,  c,)  on  the  other  hand, 
are  so  completely  covered  in  by  the  Hemispheres,  that  it  is  only 
when  the  latter  are  turned  aside  that  we  can  discern  them.  They 
differ  in  external  aspect  from  the  optic  ganglia  of  Birds  and  the  lower 
Vertebrata  ;  being  divided  by  a  transverse  furrow  into  anterior  and 
posterior  eminences, — whence  they  are  known  as  the  Corpora  Quad- 
rigemina.  The  Cerebellum  is  chiefly  remarkable  for  the  develop- 
ment of  its  lateral  parts  or  hemispheres,  and  for  the  intricate  arrange- 
ment of  the  gray  and  white  matter  in  them  (Fig.  15,  d) ;  the  central 
portion,  sometimes  called  the  vermiform  process,  is  relatively  less 
developed  than  in  the  lower  Vertebrata,  where  it  forms  the  entire 
organ.  The  Spinal  Cord  is  much  reduced  in  size,  when  compared 
with  other  parts  of  the  nervous  centres ;  the  motions  of  the  animal, 
in  this  class,  being  more  dependent  upon  its  will,  or  guided  by  its 
sensations  ;  and  the  simply  reflex  actions  bearing  a  much  smaller  pro- 
portion to  the  rest.  The  development  of  ganglionic  enlargements,  in 
accordance  with  the  presence  or  absence  of  high  locomotive  powers 
in  the  extremities,  follows  the  same  rule  as  in  the  preceding  classes. 

3.  Functions  of  the  Spinal  Cord  and  its  JVerves. 

874.  In  commencing  our  more  detailed  examination  into  the  func- 
tions of  the  different  parts  of  the  Nervous  system  in  Vertebrated 
animals,  it  seems  best  to  commence  with  the  Spinal  Cord ;  this  being 
the  portion  whose  presence  is  most  essential  to  the  continuance  of 
life.  As  already  mentioned.  Infants  are  sometimes  born  without  any 
Cerebrum  or  Cerebellum  ;  and  such  have  existed  for  several  hours  or 
even  days,  breathing,  crying,  sucking,  and  performing  various  other 
movements.  The  Cerebrum  and  Cerebellum  have  been  experiment- 
ally removed  from  Birds  and  young  Mammalia,  thus  reducing  these 
beings  to  a  similar  condition  ;  and  all  their  vital  operations  have, 
nevertheless,  been  so  regularly  performed,  as  to  enable  them  to  live 
for  weeks,  or  even  months.  In  the  Amphioxus,  as  already  remarked, 
we  have  an  example  of  a  completely-formed  adult  animal;  in  which 
no  rudiment  of  a  Cerebrum  or  Cerebellum  can  be  detected.  And  in 
ordinary  profound  sleep,  or  in  apoplexy,  the  functions  of  these  or- 


REFLEX  ACTIONS  OF  SPINAL  SYSTEM.  499 

gans  are  so  completely  suspended,  that  the  animal  is,  in  all  essential 
particulars,  in  the  same  condition  for  a  time  as  if  destitute  of  them. 
It  is  possible,  indeed,  to  reduce  a  Vertebrated  animal  to  the  condition 
(so  far  as  its  nervous  system  is  concerned)  of  an  Ascidian  MoUusk 
(§  850);  for  it  may  continue  to  exist  for  some  time,  when  not  merely 
the  Cerebum  and  Cerebellum  have  been  removed  from  above,  but 
when  nearly  the  whole  Spinal  Cord  has  been  removed  from  below, 
— that  part  only  of  the  latter  being  left,  which  is  the  centre  of  the 
respiratory  actions,  and  which  corresponds  to  the  single  ganglion  of 
the  Tunicata.  On  the  other  hand,  no  animal  can  exist  by  its  En- 
cephalon  alone,  the  Spinal  Cord  being  destroyed  or  removed  ;  for 
the  reflex  actions  of  the  latter  are  so  essential  to  the  continuance  of 
its  respiration,  and  consequently  of  its  circulation,  that  if  they  be  sus- 
pended (by  the  destruction  of  the  portion  of  the  cord  which  is  con- 
cerned in  them),  all  the  organic  functions  must  soon  cease. 

875.  Although  the  Spinal  Cord  was  formerly  regarded  as  little  else 
than  a  bundle  of  nerves  proceeding  from  the  Brain,  yet  its  true  rank, 
as  a  distinct  centre  of  nervous  action,  is  now  universally  admitted. 
That  the  actions  performed  by  it  are  of  a  purely  reflex  nature, — con- 
sisting in  the  excitement  of  muscular  movements,  in  respondence  to 
external  impressions,  without  the  necessary  intervention  of  sensation, 
— appears  to  be  a  necessary  inference,  from  the  facts  that  have  been 
brought  to  light  by  experiment  and  observation.  Experiments  on 
the  nature  of  this  function  are  best  made  upon  cold-blooded  animals ; 
as  their  general  functions  are  less  disturbed  by  the  effects  of  severe 
injuries  of  the  nervous  system,  than  those  of  Birds  and  Mammals. 
When  the  Cerebrum  has  been  removed,  or  its  functions  have  been 
suspended  by  a  severe  blow  upon  the  head,  a  variety  of  motions  may 
be  excited  by  their  appropriate  stimuli.  Thus,  if  the  edge  of  the  eye- 
lid be  touched  with  a  straw,  the  lid  immediately  closes.  If  a  candle 
be  brought  near  the  eye,  the  pupil  contracts.  If  liquid  be  poured  into 
the  mouth,  or  a  solid  substance  be  pushed  within  the  grasp  of  the 
muscles  of  deglutition,  it  is  swallowed.  If  the  foot  be  pinched,  or 
burned  with  a  lighted  taper,  it  is  withdrawn ;  and  (if  the  animal  ex- 
perimented on  be  a  Frog)  the  animal  will  leap  away,  as  if  to  escape 
from  the  source  of  irritation.  If  the  cloaca  be  irritated  with  a  probe, 
the  hind  legs  will  endeavour  to  push  it  away. 

876.  Now  the  performance  of  these,  as  well  as  of  other  movements, 
many  of  them  most  remarkably  adapted  to  an  evident  purpose,  might 
be  supposed  to  indicate,  that  sensations  are  called  up  by  the  impres- 
sions ;  and  that  the  animal  can  not  on\y  feel ^  but  can  voluntarily  di- 
rect its  movements,  so  as  to  get  rid  of  the  irritation  which  annoys  it. 
But  such  an  inference  would  be  inconsistent  with  other  facts. — In 
the  first  place,  the  motions  performed  by  an  animal  under  such 
circumstances  are  never  spontaneous,  but  are  always  excited  by  a 
stimulus  of  some  kind.  Thus,  a  decapiated  Frog,  after  the  first  vio- 
lent convulsive  movements  occasioned  by  the  operation  have  passed 
away,  remains  at  rest  until  it  is  touched ;  and  then  the  leg,  or  its 


500  REFLEX  ACTIONS  OF  SPINAL  SYSTEM. 

■whole  body,  may  be  thrown  into  sudden  action,  which  immediately 
subsides  again.  In  the  same  manner,  the  act  of  swallowing  is  not 
performed,  except  when  it  is  excited  by  the  contact  of  food  or  liquor; 
and  even  the  respiratory  movements,  spontaneous  as  they  seem  to  be, 
would  not  continue,  unless  they  were  continually  re-excited  by  the 
presence  of  venous  blood  in  the  vessels.  These  movements  are  all 
necessarily  linked  with  the  stimulus  that  excites  them  ; — that  is,  the 
same  stimulus  wull  always  produce  the  same  movement,  when  the 
condition  of  the  body  is  the  same.  Hence  it  is  evident,  that  the  judg- 
ment and  will  are  not  concerned  in  producing  them  ;  and  that  the 
adaptiveness  of  the  movements  is  no  proof  of  the  existence  of  con- 
sciousness and  discrimination  in  the  being  that  executes  them, — the 
adaptation  being  made  for  the  being,  by  the  peculiar  structure  of  its 
nervous  apparatus,  which  causes  a  certain  movement  to  be  executed 
in  respondence  to  a  given  impression, — not  by  it.  An  animal  thus 
circumstanced  may  be  not  unaptly  compared  to  an  automaton ;  in 
which  particular  movements  adapted  to  produce  a  given  effect,  are 
produced  by  touching  certain  springs.  Here  the  adaptation  was  in 
the  mind  of  the  maker  or  designer  of  the  automaton ;  and  so  it  evi- 
dently is,  in  regard  to  the  reflex  or  consensual  movements  of  animals, 
as  well  as  with  respect  to  the  various  operations  of  their  nutritive 
system,  over  which  they  have  no  control,  yet  which  concur  most  ad- 
mirably to  a  common  end. 

877.  Again,  we  find  that  such  movements  may  be  performed,  not 
only  when  the  Brain  has  been  removed,  the  spinal  cord  remaining 
entire,  but  also  when  the  Spinal  cord  has  been  itself  cut  across,  so  as 
to  be  divided  into  two  or  more  portions, — each  of  them  completely 
isolated  from  each  other,  and  from  other  parts  of  the  nervous  centres. 
Thus,  if  the  head  of  a  Frog  be  cut  off,  and  its  spinal  cord  be  divided 
in  the  middle  of  the  back,  so  that  its  fore  legs  remain  connected  with 
the  upper  part,  and  its  hind  legs  with  the  lower,  each  pair  of  members 
may  be  excited  to  movement  by  a  stimulus  applied  to  itself;  but  the 
two  pairs  will  not  exhibit  any  consentaneous  motions,  as  they  will  do 
when  the  spinal  cord  is  undivided.  Or,  if  the  Spinal  cord  be  cut 
across,  without  the  removal  of  the  Brain,  the  lower  limbs  may  be 
excited  to  movement,  by  an  appropriate  stimulus,  though  they  are 
completely  paralyzed  to  the  will ;  whilst  the  upper  remain  under  the 
control  of  the  animal,  as  completely  as  before.  Now  it  is  not  con- 
ceivable that,  in  this  last  case,  sensation  and  volition  should  exist  in 
that  portion  of  the  spinal  cord  which  remains  connected  with  the 
nerves  of  the  posterior  extremities,  but  which  is  cut  off  from  the  brain. 
For,  if  it  were  so,  there  must  be  two  distinct  centres  in  the  same  ani- 
mal, the  attributes  of  the  brain  not  being  affected  ;  and,  by  dividing 
the  spinal  cord  into  two  or  more  segments,  we  might  thus  create  in 
the  body  of  one  animal  two  or  more  distinct  centres  of  sensation, 
independent  of  that  which  still  holds  its  proper  place  in  the  Encepha- 
lon.  To  say  that  two  or  more  distinct  centres  of  sensation  are  pre- 
sent in  such  a  case,  would  really  be  in  effect  the  same  as  saying,  that 


REFLEX  ACTIONS  OF  SPINAL  SYSTEM.  501 

there  are  two  or  more  distinct  minds  in  one  body, — which  is  mani- 
festly absurd. 

878.  But  the  best  proofs  of  the  limitation  of  the  endowments  of  the 
Spinal  Cord,  are  derived  from  the  phenomena  presented  by  the  Human 
subject,  in  cases  where  that  organ  has  suffered  injury,  by  disease  or 
accident,  in  the  middle  of  the  back.  We  find  that,  when  this  injury 
has  been  severe  enough  to  produce  the  effect  of  a  complete  division 
of  the  Cord,  there  is  not  only  a  total  want  of  voluntary  control  over 
the  lower  extremities,  but  a  complete  absence  of  sensation  also, — the 
individual  not  being  in  the  least  conscious  of  any  impression  made 
upon  them.  When  the  lower  segment  of  the  Cord  remains  sound, 
and  its  nervous  connections  with  the  limbs  are  unimpaired,  distinct 
reflex  movements  may  be  excited  in  the  limbs  by  stimuli,  directly 
applied  to  them, — as,  for  instance,  by  pinching  the  skin,  tickling  the 
sole  of  the  foot,  or  applying  a  hot  plate  to  its  surface ; — and  this  with- 
out the  least  sensation,  on  the  part  of  the  patient,  either  of  the  cause 
of  the  movement,  or  of  the  movement  itself.  This  fact,  taken  in 
connection  with  the  preceding  experiments,  both  upon  Vertebrated 
and  Articulated  animals,  distinctly  proves  that  Sensation  is  not  a 
necessary  link  in  the  chain  of  reflex  actions ;  but  that  all  which  is 
required  is  an  afferent  fibre,  capable  of  receiving  the  impression  made 
upon  the  surface,  and  of  conveying  it  to  the  centre ;  a  ganglionic  cen- 
tre, composed  of  vesicular  nervous  substance,  into  which  the  afferent 
fibre  passes ;  and  an  efferent  fibre,  capable  of  transmitting  the  motor 
impulse,  from  the  ganglionic  centre,  to  the  muscle  which  is  to  be 
thrown  into  contraction. 

879.  These  conditions  are  realized  in  the  Spinal  Cord.  We  may 
have  reflex  actions  excited  through  any  one  isolated  segment  of  it,  as 
through  a  single  ganglion  of  the  ventral  cord  of  Articulata ;  but  they 
are  then  confined  to  the  parts  supplied  by  the  nerves  of  that  segment. 
Thus,  if  the  spinal  cord  of  a  Frog  be  divided  just  above  the  origin 
of  the  crural  nerves,  the  hind-legs  may  be  thrown  into  reflex  contrac- 
tion by  various  stimuli  applied  to  themselves ;  but  the  fore  legs  will 
exhibit  no  movement  of  this  kind.  But  when  the  brain  has  been 
removed,  and  the  Spinal  Cord  is  left  entire,  movements  may  be  excited 
in  distant  parts, — as,  for  example,  in  the  fore  legs,  by  any  power- 
ful irritation  of  the  posterior  extremities, — and  vice  versa.  This  is 
particularly  well  seen  in  the  convulsive  movements,  which  take  place 
in  certain  disordered  states  of  the  nervous  system  ;  a  slight  local  irrita- 
tion being  sufficient  to  throw  almost  any  muscles  of  the  body  into  a 
state  of  energetic  action  (§  885).  And  a  similar  state  may  be  arti- 
ficially induced,  by  applying  Strychnine  (in  solution)  to  the  Spinal 
Cord  of  a  decapitated  Frog. 

880.  The  minute  Anatomy  of  the  Spinal  Cord  is  a  subject  of  great 
diflficulty  ;  and  our  notions  of  the  course  of  the  fibres  within  it  are 
rather  founded  upon  physiological  phenomena,  and  upon  the  more 
evident  structure  of  the  ventral  column  in  Articulata,  than  upon  what 
can  be  clearly  demonstrated  in  Vertebrated  animals.     The  roots  of 


502 


FUNCTIONS  OP  ROOTS  OF  SPINAL  NERVES. 


the  Spinal  nerves  are  all  distinctly  separable  into  an  interior  and  a 
posterior  fasciculus ;  and  it  is  certain  that  these  fasciculi  have  entirely 
opposite  functions.  If  they  be  laid  bare,  and  the  anterior  fasciculus 
of  any  spinal  nerve  be  touched,  violent  contractions  are  immediately 
seen  in  the  muscles  supplied  by  that  nerve ;  these  contractions  are  as 
strongly  manifested,  if  the  anterior  roots  be  be  divided,  and  their  sepa- 
rated ends  be  irritated  ;  whilst  no  such  result  follows,  whatever  amount 
of  irritation  be  applied  to  the  ends  still  in  connection  with  the  cord. 

Notwithstanding  these  violent 
movements,  the  animal  shows  lit- 
tle or  no  sign  of  pain. — On  the 
other  hand,  if  the  posterior  roots 
be  irritated,  the  animal  gives  signs 
of  acute  pain,  and  no  vigorous  mus- 
cular contractions  are  produced. 
The  movements  which  are  witness- 
ed are  evidently  of  a  reflex  nature, 
being  called  forth  through  the  ante- 
rior roots;  as  is  proved  by  their 
cessation  when  these  are  divided. 
Further,  if  the  posterior  roots  be 
divided,  and  the  separated  ends  be 
irritated,  no  effect  whatever  is  pro- 
duced ;  no  movement  is  excited  ; 
and  no  sensation  is  occasioned  ;  but 
if  the  ends  still  in  connection  with 
the  cord  be  irritated,  the  animal 
shows  signs  of  pain  as  before. — 
Hence  it  is  evident,  that  the  poste- 
rior roots  are  made  up  of  efferent 
fibres ;  that  is,  of  the  fibres  which 
convey  impressions  towards  the 
nervous  centres:  which  impressions,  if  confined  to  the  cord  itself, 
excite  reflex  actions;  whilst,  if  conveyed  to  the  brain,  they  produce 
sensations.  On  the  other  hand  it  is  equally  evident,  that  the  anterior 
roots  are  composed  of  efferent  or  motor  fibres,  which  serve  to  convey 
to  the  muscles  the  motor  impulses  originating  in  the  nervous  centres ; 
these  impulses  may  be  occasioned  by  the  reflex  action  of  the  Spinal 
cord  ;  or  they  may  descend  from  the  Brain,  where  they  have  been 
generated  by  an  act  of  the  will.  In  the  accompanying  Diagram,  the 
left  side  shows  the  supposed  composition  of  the  posterior  roots  of  the 
nerves;  and  the  right  side,  that  of  the  anterior, 

881.  The  Spinal  Cord  is  a  completely  double  tract ;  being  composed 
of  two  distinct  halves,  united  together  on  the  median  plane  by  nume- 
rous commissural  fibres.  This  union  is  much  closer  in  Man  and  the 
Mammalia  than  it  is  in  the  lower  Vertebrata;  but  the  division  is  still 
marked  externally,  by  a  deep  fissure  on  the  anterior  surface  of  the  cord, 
and  by  a  shallower  one  on  its  posterior  aspect.    Its  surface  is  traversed, 


Diagram  of  the  origins  and  terminations  of 
the  different  groups  of  nervous  fibres:— a,  a, 
vesicular  substance  of  the  spinal  cord;  &,  6,  b, 
vesicular  substance  of  the  brain ;  e,  vesicular 
substance  at  the  commencement  of  afferent 
nerve,  which  consists  of  ci,  the  cerebral  divi- 
sion, or  sensory  nerve  passing  on  to  the  brain, 
and  si,  the  spinal  division,  or  excitor  nerve, 
which  terminates  in  the  vesicular  substance  of 
the  spinal  cord  ;  on  the  other  side  we  have  the 
efferent  or  motor  nerve  proceeding  to  the  mus- 
cle rf,  likewise  consisting  of  two  divisions. — 
c3,  the  cerebral  portion,  proceeding  from, the 
brain,  and  conveying  the  influence  of  the  will 
or  of  instinct ;  and  52,  the  spinal  division,  con- 
veying the  reflex  power  of  the  spinal  cord. 


STRUCTURE  OF  THE  SPINAL  CORD.  503 

moreover,  by  two  furrows  on  each  side  ;  so  that  each  half  is  divided 
into  three  columns,  the  anterior^  lateral,  and  posterior.  The  anterior 
roots  of  the  spinal  nerves  join  the  Cord  for  the  most  part  along  the 
line  of  the  anterior  furrow;  and  the  posterior  along  the  line  of  the 
posterior  furrow;  so  that  the  middle  or  lateral  column  lies  between 
them,  the  anterior  column  being  altogether  in  front  of  them,  and  the 
posterior  column  behind  them.  When  a  transverse  section  of  the 
Cord  is  made,  it  is  seen  to  contain,  on  each  side,  a  crescentic  patch  of 
gray  or  vesicular  substance ;  the  points  of  each  crescent  are  directed 
towards  the  anterior  and  posterior  furrows  of  its  own  side  respectively ; 
whilst  the  convexities  of  the  two  crescents  approach  one  another  near 
the  median  plane,  and  are  connected  by  a  transverse  tract  of  gray  matter. 
The  remainder  of  the  cord  is  made  up  of  white  or  tubular  substance, 
the  course  of  whose  fibres  is,  for  the  most  part,  longitudinal. — The  pos- 
terior peak  of  the  crescentic  patch  of  gray  matter  approaches  very 
closely  to  the  bottom  of  the  posterior  furrow ;  whilst  the  anterior  peak 
does  not  come  into  nearly  the  same  degree  of  proximity  wuth  the  bot- 
tom of  the  anterior  furrow.  Hence  it  is  considered  by  some,  that  the 
lateral  or  middle  columns  of  the  cord,  being  much  less  completely 
isolated  from  the  anterior  columns  than  they  are  from  the  posterior, 
should  be  associated  with  the  former,  under  the  name  of  antero-lateral 
columns. 

882.  Upon  tracing  the  roots  of  the  nerves  into  the  substance  of  the 
Cord,  the  connection  of  a  part  of  their  fibres  with  its  gray  or  vesicular 
substance  is  easily  made  evident.  Of  these  fibres,  therefore,  it  serves 
as  the  proper  ganglionic  centre.  There  is  reason  to  believe,  both  from 
anatomical  investigation,  and  from  physiological  phenomena,  that,  as 
in  the  Articulata,  (§  857,)  a  part  of  the  afferent  or  excitor  fibres,  after 
traversing  the  gray  substance,  pass  out  on  the  same  side  as  the  efferent 
or  motor;  whilst  another  portion  crosses  to  the  opposite  side,  and  forms 
part  of  its  efferent  trunks.  The  continuity  of  other  fibres,  however, 
with  the  longitudinal  fibres  that  form  the  white  strands  of  the  Spinal 
Cord,  has  not  been  yet  clearly  demonstrated ;  though  the  analogy  of 
the  ventral  cord  in  Articulated  animals,  and  the  physiological  pheno- 
mena, which  show  the  direct  connection  between  the  sensory  surfaces 
and  the  brain  on  the  one  hand,  and  between  the  brain  and  the  mus- 
cles on  the  other,  would  seem  to  indicate  that  such  continuity  must 
exist.— The  relative  proportions  of  the  gray  and  white  matter  in  the 
Spinal  Cord  differ  considerably  at  its  different  parts.  Thus  in  the 
cervical  region,  there  is  an  enlargement  corresponding  with  the  origins 
of  the  nerves  that  form  the  brachial  plexus;  this  enlargement  is  partly 
caused  by  an  increase  in  the  amount  of  gray  matter;  but  the  whole  of 
the  cervical  portion  of  the  cord  contains  a  very  large  amount  of  fibrous 
structure  also.  On  the  other  hand,  there  is  a  still  greater  enlargement 
of  the  cord  in  the  lumbar  region,  at  the  part  whence  the  nerves  of  the 
lower  extremities  arise ;  and  this  enlargement  is  caused  by  the  great 
increase  in  the  amount  of  the  gray  matter  at  that  point ;  the  white  or 
fibrous  portion  constituting  but  a  comparatively  small  part  of  it.    Now 


504  REFLEX  FUNCTION  OF  THE  SPINAL  CORD. 

these  anatomical  facts  harmonize  well  with  the  physiological  views 
just  given;  for  the  actions  of  the  lower  extremities  being  much  more 
of  a  simply  reflex  nature  than  those  of  the  upper,  we  find  the  gangli- 
onic portion  of  the  spinal  cord  exhibiting  a  corresponding  increase  at 
the  origins  of  their  nerves;  whilst  the  actions  of  the  superior  extremi- 
ties being  for  the  most  part  of  a  voluntary  character,  we  find  that  the 
cord  mainly  consists,  at  the  part  with  which  their  nerves  are  connect- 
ed, of  white  fibrous  structure,  which  appears  to  convey  to  those  nerves 
the  direct  influence  of  the  brain. 

883.  It  was  supposed  by  Sir  C.  Bell  (who  was  the  first  to  deter- 
mine the  relative  functions  of  the  two  roots  of  the  spinal  nerves  in 
Vertebrated  animals),  that  the  anterior  columns  of  the  Spinal  cord 
have  a  function  corresponding  to  that  of  the  anterior  roots  of  the  spi- 
nal nerves;  and  the  posterior  columns  with  the  posterior  roots.  But 
from  the  difl5culty  of  tracing  the  connection  between  the  longitudinal 
fibres  of  the  cord  and  any  portion  of  the  roots,  it  is  at  present  impos- 
sible to  say  how  far  there  is  any  anatomical  reason  for  the  assumption 
of  this  correspondence ;  and  it  is  quite  certain,  that  the  physiological 
facts  at  present  known,  from  observation  of  the  effects  of  disease  or 
injury  upon  different  tracts  of  the  spinal  cord,  do  not  bear  out  the 
supposition.  As  to  what  the  precise  functions  of  the  several  columns 
are,  however,  it  is  not  easy  to  form  any  other  conjecture,  that  shall 
be  consistent  with  all  the  phenomena  at  present  known. 

884.  Of  the  particular  Reflex  actions  to  which  the  Spinal  Cord 
(using  that  term  in  its  limited  sense,  as  excluding  the  Medulla  Oblon- 
gata) is  subservient,  those  most  connected  with  the  organic  functions 
have  already  been  noticed.  They  are  chiefly  of  an  expulsive  kind  ; 
being  destined  to  force  out  the  contents  of  various  cavities  of  the  body. 
Thus  the  ordinary  acts  of  defecation  and  urination,  the  ejaculatio  se- 
minis,  and  parturition,  are  all  reflex  actions,  over  which  the  will  has  a 
greater  or  less  degree  of  control ;  being  able  to  keep  the  two  former 
ones  in  check,  so  long  as  the  stimulus  is  not  very  violent,  and  being 
also  capable  of  effecting  them  by  itself;  but  having  no  control  over 
the  two  latter,  either  by  way  of  acceleration  or  prevention,  when  once 
the  stimulus  by  which  they  are  excited  has  come  into  full  action. — The 
movements  of  the  posterior  extremities  are  among  the  most  remarkable 
of  those,  which  seem  due  to  the  action  of  the  proper  Spinal  Cord.  It 
has  been  already  noticed,  that  these  may  be  excited,  even  in  Man, 
when  the  spinal  cord  has  been  severed  in  the  middle  without  injury  to 
its  lower  segment ;  and  it  is  remarkable,  that  gentle  stimuli,  applied 
to  the  skin  of  the  sole  of  the  foot,  appear  the  most  capable  of  producing 
them.  We  have  seen  how  completely,  in  the  lower  animals,  the  acts 
of  progression  maybe  sustained,  by  the  repeated  stimulus  of  the  con- 
tact of  the  ground,  or  of  fluid,  without  any  influence  from  the  cephalic 
ganglia  ;  the  power  of  these  being  limited,  it  would  seem,  to  the  con- 
trol and  direction  of  them.  And  there  is  strong  reason  to  believe 
that,  so  far  as  the  ordinary  acts  of  locomotion  are  concerned,  the 
movements  of  the  inferior  extremities  in  Man  may  be  performed  on  the 


ACTS  OF  LOCOMOTION.— CONVULSIVE  DISORDERS.  505 

same  plan,  being  continued  by  reflex  power,  when  once  set  in  action 
by  the  will,  whilst  we  are  walking  steadily  onwards, — the  mind  being 
at  the  same  time  occupied  by  some  train  of  thought  which  engrosses 
its  whole  attention.  There  are  few  persons  to  whom  it  has  not  occa- 
sionally happened  that,  on  awaking  (as  it  were)  from  their  revery, 
they  have  found  themselves  in  a  place  very  different  from  that  to 
which  they  had  intended  going  ;  and  even  when  the  mind  is  sufficient- 
ly on  the  alert  to  guide,  direct,  and  control  the  motions  of  the  limbs, 
their  separate  actions  appear  to  be  performed  without  any  direct  agency 
of  the  will.  It  is  certain  that,  in  Birds,  the  movements  of  flight  may 
be  performed  after  the  removal  of  the  Cerebrum. 

885.  There  are  many  irregular  or  abnormal  reflex  actions,  performed 
through  the  instrumentality  of  the  Spinal  Cord,  the  study  of  which  is 
of  the  highest  importance  to  the  Medical  Man.  It  is  probable  that 
all  Convulsive  movements  are  produced  through  its  agency  and  that  of 
the  Medulla  Oblongata ;  for  it  has  been  found,  by  repeated  experiments, 
that  these  movements  are  never  produced  by  injuries  of  the  Cerebral 
hemispheres. — Convulsive  movements  may  be  of  three  kinds.  1.  They 
may  be  simply  reflex;  being  the  natural  result  of  some  extraordinary 
irritation.  2.  They  may  be  simply  centric  ;  depending  upon  a  pecu- 
liar condition  of  the  ganglionic  centre  of  the  Spinal  Cord,  which  oc- 
casions muscular  movements  without  any  stimulation.  3.  They  may 
depend  upon  the  combined  action  of  both  principles;  the  nervous  cen- 
tres being  in  a  very  irritable  state,  which  causes  very  slight  irritations 
(such  as  would  otherwise  be  inoperative)  to  excite  violent  reflex  or 
convulsive  movements.  This  last  is  by  far  the  most  common  cause  of 
the  convulsive  actions,  that  occur  in  various  diseased  conditions  of  the 
system.  Thus,  convulsions  are  not  unfrequent  in  children,  during  the 
period  of  teething;  being  produced  by  the  irritation  which  results 
from  the  pressure  of  the  tooth  as  it  rises  against  the  unyielding  gum. 
In  this  case,  the  stimulus  would  scarcely  be  sufficient  to  produce  the 
violent  result,  were  it  not  for  a  peculiarly  excitable  state  of  the  Spinal 
Cord,  brought  about  by  various  causes.  In  like  manner,  when  such 
an  excitable  state  exists,  convulsions  may  be  occasioned  by  the  pre- 
sence of  intestinal  worms,  of  irritating  substances,  or  even  simply  of 
undigested  matters  in  the  alimentary  canal ;  and  will  cease  as  soon 
as  they  are  cleared  out — in  the  same  manner  as  the  convulsions  of 
teething  may  often  be  at  once  checked — by  the  free  lancing  of  the 
gums. 

886.  The'  influence  of  the  condition  of  the  Spinal  Cord  itself  is 
peculiarly  seen  in  the  convulsive  diseases  termed  Hydrophobia,  Te- 
tanus, Epilepsy,  and  Hysteria.  In  the  first  of  these,  not  only  the 
Spinal  Cord,  but  the  Medulla  Oblongata,  and  the  ganglia  of  Special 
Sense,  are  involved  ;  their  peculiar  condition  being  the  result,  it 
would  appear,  of  the  introduction  of  a  poison  into  the  blood.  It  is 
most  remarkable  that  the  Brain  should  so  completely  escape  its  in- 
fluence. When  the  state  of  intense  excitability  in  these  centres  is 
once  established,  the  slightest  stimulus  is  sufficient  to  bring  about 


506  PECULIARITIES  OF  CERTAIN  SPINAL  NERVES. 

convulsive  movements  of  the  utmost  violence.  It  is  characteristic 
of  this  complaint,  that  the  stimuli  most  effectual  in  exciting  the 
movements,  are  those  which  act  through  the  nerves  of  special  sense  ; 
thus  the  sight  or  the  sound  of  water  will  bring  on  the  paroxysm ;  and 
any  attempt  to  taste  it  increases  the  severity  of  the  convulsions. — 
In  Tetanus  there  appears  to  be  a  similarly  excitable  state  of  the 
Spinal  Cord  and  Medulla  Oblongata,  not  involving  the  ganglia  of 
special  sense.  This  may  be  the  result  of  causes  altogether  internal, 
as  in  the  idiopathic  form  of  the  disease ;  in  which  the  condition  ex- 
actly resembles  that  which  may  be  artificially  induced  by  the  admin- 
istration of  Strychnine,  or  by  its  application  to  the  cord.  Or  it  may 
be  first  occasioned  by  some  local  irritation,  as  that  of  a  lacerated 
wound ;  the  irritation  of  the  injured  nerve  being  propagated  to  the 
nervous  centres,  and  establishing  the  excitable  state  in  them.  When 
the  complaint  has  once  established  itself,  the  removal  of  the  original 
cause  of  irritation  (as  by  the  amputation  of  the  injured  limb)  is  sel- 
dom of  any  avail ;  since  the  slightest  impressions  upon  almost  any 
part  of  the  body,  are  suflficient  to  excite  the  tetanic  spasm. — In  like 
manner.  Epilepsy,  which  consists  in  convulsive  actions  with  tem- 
porary suspension  of  the  functions  of  the  brain,  may  result  from  the 
irritation  of  local  causes,  like  the  convulsions  of  teething;  and  may, 
like  them,  cease  when  the  sources  of  irritation  are  removed.  But 
when  it  becomes  confirmed,  it  seems  to  involve  a  disorder  of  the 
nervous  centres,  which  no  local  treatment  can  influence. 

887.  These  and  other  forms  of  Convulsive  disorder,  when  produc- 
tive of  a  fatal  result,  usually  act  by  suspending  the  respiratory  move- 
ments ;  the  muscles  which  effect  these  being  fixed  by  the  spasms,  so 
that  the  air  cannot  pass  either  in  or  out,  and  suffocation  takes  place 
as  completely  as  if  the  entrance  to  the  air-passages  were  closed.  It 
is  remarkable  that  every  one  of  them  may  be  imitated  by  Hysteria;  a 
state  of  the  nervous  system  in  which  there  is  a  peculiar  excitability, 
but  in  which  there  is  no  such  fixed  tendency  to  irregular  action  as 
would  indicate  any  positive  disease, — one  form  of  convulsion  often 
taking  the  place  of  another,  at  short  intervals,  with  the  most  wonder- 
ful variety.  It  will  often  be  found,  that  the  convulsions  may  be  im- 
mediately traced  to  some  local  irritation  ;  thus  they  are  particularly 
liable  to  occur  at  the  catamenial  periods,  especially  if  the  menstrual 
flux  be  deficient.  But  the  liability  to  them,  resulting  from  the  pecu- 
liar excitability  of  the  nervous  system,  can  only  be  treated  by  such 
constitutional  remedies  as  tend  to  increase  its  vigour  and  to  promote 
its  normal  activity. 

888.  The  statement  that  the  spinal  nerves  arise  by  double  roots,  is 
not  without  exception  as  regards  some,  which  arise  from  its  cranial 
prolongation,  and  which  are  distributed  to  the  parts  of  the  head  and 
neck.  Th.^  first  spinal  nerve,  ov  sub-occipital^  (the  10th  pair  of  Wil- 
lis,) not  unfrequently  arises  by  a  single  set  of  roots,  from  the  anterior 
portion  of  the  cord ;  and  it  is  then  purely  motor  except  in  virtue  of 
its  inosculation  with  other  nerves.     The  Hypoglossal  (9th  pair  of 


STRUCTURE  OF  THE  MEDULLA  OBLONGATA.  507 

Willis)  appears  to  be  also  a  purely  motor  nerve ;  arising  by  one  set 
of  roots;  and  being  distributed  entirely  to  the  muscles  of  the  tongue  ; 
which  organ  derives  its  sensibility  from  other  nerves.  The  Glosso- 
pharyngeal usually  arises  from  a  single  set  of  roots,  and  these  corre- 
spond with  the  posterior  roots  of  the  spinal  nerves  ;  in  some  animals, 
however,  and  occasionally  in  man,  there  is  a  distinct  anterior  root, 
and  the  nerve  acquires  direct  motor  functions.  It  may  in  some  re- 
spects be  considered  as  making  up,  with  the  preceding,  an  ordinary 
spinal  nerve.  The  Spinal  Accessory,  again,  appears  to  be  chiefly  or 
entirely  a  motor  nerve  at  its  origin ;  and  in  like  manner  the  Pneumo- 
gastric,  or  Par  Vagum,  seems  at  its  roots  to  correspond  with  the  pos- 
terior roots  of  the  ordinary  spinal  nerves,  and  to  execute  functions 
analogous  to  theirs ;  but  these  two  nerves  exchange  fibres,  so  that 
each  acquires  in  part  the  endowments  of  the  other.  The  Facial  nerve, 
(or  portio  dura  of  the  7th,)  which  is  the  nerve  that  supplies  the  mus- 
cles of  the  head  in  general,  arises  by  a  single  root,  and  is  exclusively 
motor  in  its  properties. — except  in  branches  which  have  received 
sensory  filaments  by  inosculation  with  other  nerves.  The  same  is 
the  case,  also,  with  the  Motor  JVerves  of  the  Orbit,  (the  6th,  4th  and 
3d,  of  Willis,)  which  arise  by  single  roots,  and  which  have  no  sen- 
sory endowments  but  those  which  they  obtain  by  inosculation  with 
the  Fifth  pair. — On  the  other  hand,  the  Fifth  pair  arises  by  a  double 
root ;  that  which  corresponds  to  the  anterior  or  motor  root  to  the  spi- 
nal nerves  is  very  small,  however,  and  only  enters  the  third  division 
of  the  nerve,  which  supplies  the  muscles  concerned  in  mastication  ; 
the  other  root,  corresponding  with  the  posterior  roots  of  the  spinal 
nerves,  is  of  large  size,  and  its  branches  are  distributed  to  the  face  and 
head,  supplying  them  with  sensibility.  Thus  the  sensory  division  of 
the  fifth  pair  being  distributed,  not  merely  to  the  same  parts  with  its 
motor  division  but  also  to  the  parts  which  derive  their  motor  endow- 
ments from  the  Facial  nerve,  and  from  the  nerves  of  the  orbit,  may 
be  regarded  as  making  up,  together  with  all  of  them,  one  ordinary 
Spinal  nerve. 

4.  Functions  of  the  Medulla  Oblongata, 

889.  This  portion  of  the  nervous  centres,  as  already  stated,  does 
not  differ  in  any  essential  particular  from  the  Spinal  Cord,  of  which 
it  may  be  considered  as  a  cranial  prolongation.  But  the  arrangement 
of  its  constituent  parts  is  peculiar ;  being  the  medium  by  which  the 
various  strands  of  the  Spinal  Cord  are  connected  with  the  different 
portions  of  the  Encephalon  :  and  it  is  also  remarkable  as  being  the 
ganglionic  centre,  concerned  in  the  maintenance  of  the  action  of  re- 
spiration, and  in  the  ingestion  of  food.  Four  principal  tracts  of  nerv- 
ous matter  may  be  distinguished  in  each  of  its  lateral  halves.  These 
are,  anteriorly,  the  anterior  pyramids ;  next,  the  olivary  bodies;  next, 
the  restiform  bodies;  and,  lastly,  the  posterior  pyramids.  The  fol- 
lowing are  the  principal  connections  of  these  different  strands,  with 


508       STRUCTURE  AND  FUNCTIONS  OF  MEDULLA  OBLONGATA. 

the  several  parts  of  the  Encephalon  above,  and  of  the  Spinal  Cord 
below. 

890.  The  Anterior  Pyramids,  "which  consist  entirely  of  fibrous 
structure,  may  be  said  to  connect  the  motor  fibres  of  the  Cerebral 
Hemispheres  with  the  antero-lateral  columns  of  the  Spinal  Cord.  Of 
the  fibres  of  which  they  are  composed,  a  large  part  decussate  ;  those 
that  proceed  from  the  right  hemisphere,  passing  into  the  left  side  of 
the  cord ;  and  those  from  the  left  hemisphere  into  the  right  side  of 
the  cord, — an  arrangement  which  fully  explains  the  fact,  that  in  Hemi- 
plegia, the  paralytic  aflfection  of  the  body  is  on  the  opposite  side  to 
that  of  the  face,  the  latter  corresponding  with  the  side  of  the  brain  in 
which  the  disease  may  exist.  A  small  proportion  of  the  fibres  of  the 
anterior  pyramids  does  not  decussate  ;  and  this  passes  down,  with 
fibres  from  the  olivary  columns,  into  the  anterior  columns  of  the  cord ; 
whilst  the  decussating  fibres  dip  more  deeply  away  from  the  anterior 
surface  of  the  cord,  and  connect  themselves  rather  with  its  middle 
columns. 

891.  The  Olivary  bodies  are  composed  externally  of  fibrous  struc- 
ture; their  fibres  being  connected  above  with  the  Cerebral  Hemi- 
spheres and  Corpora  Quadrigemina;  and  below  with  the  antero-lateral 
columns  of  the  Spinal  Cord.  But  beneath  the  fibrous  layer  we  find 
a  large  mass  of  vesicular  matter,  the  presence  of  which  gives  to  the 
Medulla  Oblongata  its  ganglionic  character.  This  seems  to  be  the 
centre  of  the  respiratory  nerves ;  it  is  continuous  with  the  gray  matter 
of  the  Spinal  Cord  below,  and  with  that  of  certain  parts  of  the  Ence- 
phalon above ;  and,  from  its  peculiar  aspect,  it  is  known  as  the  corpus 
dentatum. 

892.  The  Restiform  columns  are  continuous  above  with  the  fibres 
of  the  hemispheres  of  the  Cerebellum ;  and  below  they  pass,  without 
decussation,  chiefly  into  the  posterior  columns  of  the  spinal  cord, — a 
band  of  «rcz/brm  fibres,  however,  crossing  over  to  the  anterior  columns 
on  each  side. 

893.  The  Posterior  Pyramids  are  two  small  strands  of  fibrous 
structure,  lying  between  the  two  restiform  bodies ;  and  occupying  the 
portion  of  the  Medulla  Oblongata  on  either  side  of  the  posterior 
median  furrow.  They  seem  to  stop  short  at  the  fourth  Ventricle  ; 
and  it  has  not  yet  been  ascertained  whether  they  have  any  connec- 
tion with  the  higher  parts  of  the  Encephalon.  Below,  they  assist  in 
forming  the  posterior  columns  of  the  Spinal  Cord  ;  and,  if  it  be  true 
that  they  have  no  connection  with  the  brain,  we  may  assign  to  them 
the  function  of  connecting  the  diflferent  segments  of  the  cord  with  each 
other. 

894.  The  functions  of  the  Medulla  Oblongata  are,  therefore,  of  a 
double  character; — to  bring  the  higher  parts  of  the  Encephalon  into 
connection  with  the  Spinal  Cord  and  the  Nerves  that  issue  from  it ; 
— and  to  serve  as  a  centre  for  the  reflex  movements,  performed 
through  the  nerves  that  issue  from  it.  In  both  respects  it  corresponds 
precisely  with  any  segment  of  the  Spinal  Cord  itself;  and  there  is  no 


REFLEX  ACTIONS  OF  MEDULLA  OBLONGATA.  509 

reason  to  believe,  that  it  possesses  any  other  or  more  special  endow- 
ments. The  importance,  however,  of  the  reflex  acts  of  Respiration 
and  Deglutition,  over  which  it  presides,  causes  this  portion  of  the 
Medulla  to  be  the  one  whose  integrity  is  most  essential  to  the  pre- 
servation of  life  ;  and  therefore  it  seems  to  possess  a  character  more 
distinctive  than  it  really  has. 

895.  The  chief  excitor  nerve  of  the  respiratory  movements,  as  al- 
ready stated  (§§  685-687)  is  the  afferent  portion  of  the  Par  Vagum; 
but  the  afferent  portion  of  the  Fifth  pair  is  also  a  powerful  excitor ; 
and  the  afferent  portions  of  all  the  spinal  nerves,  conveying  impres- 
sions from  the  general  surface  of  the  body,  are  also  capable  of  con- 
tributing to  the  excitement  necessary  for  the  production  of  the  move- 
ment.— The  chief  motor  nerves  are  the  phrenic  and  intercostals ; 
which,  though  issuing  from  the  Cord  at  a  considerable  space  lower 
down,  probably  originate  in  the  Medulla  oblongata.  The  motor 
portions  of  several  other  spinal  nerves  are  also  partly  concerned  ;  as 
are  also  the  Facial  nerve,  the  motor  portion  of  the  Par  Vagum,  and 
the  Spinal  Accessory.  The  ordinary  movements  of  Respiration 
involve  little  action  of  any  motor  nerves  but  the  Phrenic  and  Inter- 
costal ;  and  it  is  only  when  an  excess  of  the  stimulus  (produced  for 
example  by  too  long  a  suspension  of  the  aerating  process)  excites 
extraordinary  movements,  that  the  nerves  last  enumerated  are  called 
into  action. 

896.  The  acts  o^  Prehension  of  food  with  lips,  and  oi  Mastication^ 
though  usually  effected  by  voluntary  power  in  the  adult,  seem  to  be 
capable  of  taking  place  as  a  part  of  the  reflex  operation  of  the  Me- 
dulla Oblongata,  in  the  Infant,  as  in  the  lower  animals.  This  is 
particularly  evident  in  the  prehension  of  the  nipple  by  the  lips  of  the 
infant,  and  the  act  of  suction  which  the  contact  of  that  body  (or  of 
any  resembling  it)  seems  to  excite.  The  experiments  provided  for 
us  by  nature,  in  the  production  of  anencephalous  monstrosities,  fully 
prove  that  the  integrity  of  the  nervous  connection  of  the  lips  and 
respiratory  organs  with  the  Medulla  Oblongata,  is  alone  sufficient  for 
the  performance  of  this  action ;  and  experiments  upon  young  animals, 
from  which  the  brain  has  been  removed,  establish  the  same  fact. 
Thus  Mr.  Grainger  found  that,  upon  introducing  his  finger,  moistened 
with  milk,  or  with  sugar  and  water,  between  the  lips  of  a  puppy  thus 
mutilated,  the  act  of  suction  was  excited ;  and  not  merely  the  act  of 
suction  itself,  but  other  movements  having  a  relation  to  it ;  for  as  the 
puppy  lay  on  its  side,  sucking  the  finger,  it  pushed  out  its  feet,  in 
the  same  manner  as  young  pigs  exert  theirs  in  compressing  the  sow's 
dugs.  This  action  seems  akin  to  many  of  those  by  which  the  lower 
animals  take  in  their  food  ;  and  we  may  thus  recognize  in  the  Medulla 
Oblongata  a  distinct  centre  of  reflex  action  for  the  reception  and  deglu- 
tition of  aliment,  analogous  to  the  stomato- gastric  ganglia  of  Inverte- 
brated  animals. 

897.  In  the  movements  o^  Deglutition^  which,  as  formerly  explained, 
(§  453,)  are  purely  reflex,  the  "chief  excitor  is  undoubtedly  the  affe- 


510  GANGLIA  OF  SPECIAL  SENSE  IN  MAN. 

rent  portion  of  the  Glosso-pharyngeal  nerve.  It  is  found  that,  if  the 
trunk  of  this  nerve,  or  its  pharyngeal  (but  not  its  lingual)  branches, 
be  pinched,  pricked,  or  otherwise  irritated,  whilst  still  in  connection 
with  the  Medulla  Oblongata,  the  movements  concerned  in  the  act  of 
swallowing  are  excited.  The  same  occurs  if,  when  the  trunk  of  the 
Glosso-pharyngeal  has  been  divided,  the  cut  extremity  in  connection 
with  the  Medulla  Oblongata  is  irritated  ;  but  little  or  no  muscular 
contraction  is  produced  by  irritation  of  the  separated  extremity  ; 
whence  it  is  apparent,  that  the  Glosso-pharyngeal  has  little  or  no  di- 
rect motor  power,  but  acts  as  an  excitor.  In  this  it  appears  to  be 
assisted  by  the  branches  of  the  Fifth  pair  distributed  upon  the  fauces  ; 
and  probably,  also,  by  the  branches  of  the  Superior  Laryngeal  distri- 
buted upon  the  Pharynx.  The  motor  influence,  which  is  generated 
in  respondence  to  the  stimulus  thus  conveyed,  appears  to  act  chiefly 
through  the  branches  of  the  Par  Vagum,  which  are  distributed  to  most 
of  the  muscles  concerned  in  swallowing;  but  the  Facial,  the  Hypo- 
glossal, the  motor  portion  of  the  Fifth,  and  perhaps  also  the  motor 
portions  of  some  of  the  Cervical  nerves,  are  also  concerned  in  the 
movement,  and  may  effect  it,  though  with  difficulty,  after  the  pha- 
ryngeal branches  of  the  Par  Vagum  have  been  divided. 

898.  In  the  propulsion  of  the  food  down  the  (Esophagus,  to  which 
the  glosso-pharyngeal  nerve  does  not  extend,  the  muscular  contrac- 
tion, so  far  as  it  is  of  a  reflex  nature,  (§  455,)  must  depend  upon  the 
oesophageal  branches  of  the  Par  Vagum  alone  ;  their  afferent  portion 
being  the  excitor,  and  their  motor  portion  givi'ng  the  requisite  stimu- 
lus to  the  muscles.  The  same  must  be  the  case  in  regard  to  the  mus- 
cular contractions  of  the  cardiac  and  pyloric  sphincters,  and  of  the 
walls  of  the  stomach,  so  far  as  regards  their  dependence  upon  the 
nervous  system  at  all ;  but  the  degree  of  this  is  doubtful. 

899.  There  are  other  reflex  actions  of  the  Medulla  oblongata,  con- 
nected with  the  regulation  of  the  aperture  of  the  Glottis ;  these,  which 
are  effected  through  the  superior  and  inferior  laryngeal  branches  of 
the  Par  Vagum,  will  be  better  noticed  when  the  actions  of  the  La- 
rynx are  under  consideration. — In  like  manner,  the  reflex  action  con- 
cerned in  the  regulation  of  the  aperture  of  the  Pupil  will  be  more 
conveniently  noticed  in  the  sketch  to  be  presently  given  of  the  Physi- 
ology of  Vision. 

5.  Functions  of  the  Sensory  Ganglia. 

900.  All  the  nerves  of  Sensation,  both  general  and  special,  may  be 
traced  into  a  series  of  ganglionic  masses  lying  at  the  base  of  the  brain  ; 
which  seem  to  constitute  their  own  particular  centres.  Thus  we  have 
seen  in  Fishes,  the  Olfactive,  Optic,  and  Auditory  ganglia,  marked 
out  as  such,  by  the  termination  of  the  nerves  proceeding  from  the 
organs  of  smell,  sight,  and  hearing,  in  these  masses  respectively. 
These  ganglia  bear  an  evident  correspondence  with  the  cephalic  gan- 
glia of  the  Invertebrata ;  which  must  chiefly,  however,  be  regarded 


GANGLIA  OF  SENSE  IN  MAN.  '  511 

as  optic  ganglia,  since  the  development  of  the  eyes  far  surpasses  that 
of  the  other  organs  of  special  sense.  On  the  other  hand,  they  find 
their  representatives  in  certain  organs  at  the  base  of  the  brain,  in  Man 
and  the  higher  Mammalia ;  which,  though  small  in  proportion  to  the 
whole  Encephalon,  are  capable  of  being  clearly  marked  out,  as  the 
ganglionic  centres  of  the  several  nerves  of  sense.  Thus,  anteriorly, 
we  have  the  Olfactive  ganglia,  in  what  are  commonly  termed  the  bul- 
bous expansions  of  the  Olfactive  nerve ;  which,  however,  are  real 
ganglia,  containing  gray  or  vesicular  substance  ;  and  their  separation 
from  the  general  mass  of  the  Encephalon,  by  the  peduncles  or  foot- 
stalks commonly  termed  the  trunks  of  the  olfactory  nerves,  finds  its 
analogy  in  many  species  of  Fish  (§  869).  The  ganglionic  nature  of 
these  masses  is  more  evident  in  many  of  the  lower  Mammalia,  in 
which  the  organ  of  smell  is  highly  developed,  than  it  is  in  Man,  whose 
olfactive  powers  are  comparatively  moderate. — At  some  distance  be- 
hind these,  we  have  the  representatives  of  the  Optic  Ganglia,  in  the 
Tubercula  Quadrigemina^  to  which  the  principal  part  of  the  roots  of 
the  Optic  nerve  may  be  traced.  Although  these  bodies  are  so  small 
in  Man  as  to  be  apparently  insignificant,  yet  they  are  much  larger, 
and  form  a  more  evidently  important  part  of  the  Encephalon,  in  many 
of  the  lower  Mammalia ;  though  still  presenting  the  same  general 
aspect. — The  Auditory  ganglia  seldom  form  distinct  lobes  or  projec- 
tions ;  but  are  usually  lodged  in  the  substance  of  the  Medulla  Ob- 
longata. Their  real  character  is  most  evident  in  certain  Fishes,  as 
the  Carp  ;  in  which  we  find  the  Auditory  Nerve  having  as  distinct  a 
ganglionic  centre  as  the  Optic.  In  higher  animals,  however,  we  are 
able  to  trace  the  Auditory  nerve  into  a  small  mass  of  gray  matter, 
which  lies  on  each  side  of  the  fourth  Ventricle ;  and  although  this  is 
lodged  in  the  midst  of  parts  whose  function  is  altogether  diflferent,  yet 
there  seems  no  reason  for  doubting  that  it  has  a  character  of  its  own, 
and  that  it  is  really  the  ganglion  of  the  auditory  nerve. — We  are  not 
able  to  fix  upon  any  such  mass  of  gray  matter  as  the  distinct  Gusta- 
tory ganglion  ;  nor  is  it  necessary  to  attempt  to  do  so  ;  for,  as  we  shall 
see  hereafter,  there  is  strong  reason  to  regard  the  sense  of  Taste  as 
only  a  refined  kind  of  Touch. 

901.  At  the  base  of  the  Cerebral  Hemispheres,  we  find  two  gan- 
glionic masses  on  either  side,  through  which  all  the  fibres  pass  that 
connect  the  Hemispheres  with  the  Medulla  Oblongata.  These  are  the 
Corpora  Striata,  and  Thalami  Optici.  Upon  tracing  forwards  the  tract 
of  fibres  that  ascends  from  the  anterior  Pyramids,  we  find  it  passing 
chiefly  into  the  Corpora  Striata;  whilst,  if  we  follow  the  Olivary  column, 
we  shall  find  it  to  enter  the  Thalami.  The  anterior  continuations  of 
these  two  columns  together  form  the  Crura  Cerebri,  or  peduncles  of 
the  Cerebrum ;  and  the  relative  functions  of  the  two  layers  of  which 
it  is  composed  (which  may  be  very  readily  isolated)  are  clearly  indi- 
cated, by  the  characters  of  the  nerves  that  are  respectively  connected 
with  them.  Thus  along  the  tract  that  passes  from  the  anterior 
Pyramids  to  the  Corpora  Striata,  we  have  none  but  motor  nerves ; 


512 


THALAMI  OPTICI,  AND  CORPORA  STRIATA. 


Fig.  144. 


whilst  along  the  tract  that  connects  the  Olivary  columns  with  the 
Thalami,  there  are  none  but  sensory  nerves.  The  fibres  of  the  Crura 
Cerebri,  after  entering  these  masses,  seem  to  radiate  towards  all  parts 

of  the  surface  of  the  hemi- 
spheres, at  whose  base  they 
are  situated ;  but  some  of  them 
probably  find  a  ganglionic 
centre  in  these  bodies  them- 
selves ;  since  their  substance 
contains  a  considerable  amount 
of  gray  matter.  It  may  be 
regarded  as  not  improbable, 
then,  that  we  may  consider 
the  Thalami  as  the  ganglionic 
centres  of  common  sensation ; 
standing  in  the  same  relation 
to  the  sensory  nerves,  that 
converge  from  various  parts 
of  the  body  towards  the  En- 
cephalon,  as  do  the  Optic  and 
other  ganglia  to  their  nerves 
of  special  sensation.  And  as 
these  last  give  origin  (as  will 
be  presently  shown)  to  motor 
fibres,  so  may  we  regard  the 
ganglionic  matter  of  the  Cor- 
pora Striata  as  probably  shar- 
ing in  the  same  function  ;  giv- 
ing origin  to  the  motor  fibres, 
which  produce  the  respondent 
consensual  movements; — ^just 
as  the  anterior  peak  of  gray 
matter  in  the  Spinal  Cord 
gives  exit  to  the  motor  fila- 
ments, which  effect  the  reflex 
movements  excited  through 
the  afferent  fibres  that  form 
part  of  the  posterior  roots. — 
It  must  be  remembered',  how- 
ever, that  a  large  proportion 
of  the  fibres,  that  can  be  traced  from  the  Medulla  Oblongata,  through 
the  Crura  Cerebri,  into  the  Thalami  Optici  and  Corpora  Striata,  pass 
through  these  latter  masses,  to  become  continuous  with  the  fibres 
radiating  from  them  to  the  surface  of  the  Cerebral  hemispheres.  Upon 
these,  there  is  no  reason  to  believe  that  their  ganglionic  matter  exerts 
any  influence. 

902.  The  functions  of  this  group  of  ganglia  may  be  partly  inferred 
from  the  results  of  experiments ;  and  these  have  been  chiefly  made 


The  base  of  ihe  Brain,  upon  which  several  sections 
have  been  made,  showing  the  distribution  of  the  diverg- 
ing fibres.  1.  The  medulla  oblongata.  2.  One-half  of 
the  pons  Varolii.  3.  The  crus  cerebri  crossed  by  the 
optic  nerve  (4).  and  spreading  out  into  the  hemisphere 
to  form  the  corona  radiata.  5.  The  optic  nerve  near  its 
origin.  6.  The  olfactory  nerve.  7.  The  corpora  albi- 
cantia.  On  the  right  side  a  portion  of  the  brain  has 
been  removed  to  show  the  distribution  of  the  diverging 
fibres.  8.  The  fibres  of  the  corpus  pyramidale  passing 
through  the  substance  of  the  pons  Varolii.  9.  The  fibres 
passing  through  the  thalamus  opticus.  10.  The  fibres 
passing  through  the  corpus  striatum.  11.  Their  distri- 
bution to  the  hemispheres.  12.  The  fifth  nerve ;  its  two 
roots  may  be  traced,  the  one  forwards  to  the  fibres  of 
the  corpus  pyramidale,  the  other  backwards  to  the 
fasciculi  teretes.  13.  The  fibres  of  the  corpus  pyrami- 
dale, which  pass  outwards  with  the  corpus  resliforme 
into  the  substance  of  the  cerebellum;  these  are  the  arci- 
form  fibres  of  Solly.  The  fibres  referred  to  are  those 
below  the  numeral,  the  numeral  itself  rests  upon  the 
corpus  olivare.  14.  A  section  through  one  of  the  hemi 
spheres  of  the  cerebellum,  showing  the  corpus  rhom- 
boideum  in  the  centre  of  its  while  substance ;  the  arbor 
vitae  is  also  beautifully  seen.  15.  The  opposite  hemi- 
sphere of  the  cerebellum. 


FUNCTIONS  OF  SENSORY  GANGLIA.  513 

upon  the  Optic  ganglia,  or  Corpora  Quadrigemina.  The  partial  loss 
of  the  ganglion  on  one  side  produces  temporary  blindness  in  the  eye 
of  the  opposite  side,  and  partial  loss  of  muscular  power  on  the  oppo- 
site side  of  the  body  ;  and  the  removal  of  a  larger  portion,  or  the  com- 
plete extirpation  of  it,  occasions  permanent  blindness  and  immobility 
of  the  pupil,  and  temporary  muscular  weakness,  on  the  opposite  side. 
This  temporary  disorder  of  the  muscular  system  sometimes  manifests 
itself  in  a  tendency  to  move  on  the  axis,  as  if  the  animal  were  giddy ; 
and  sometimes  in  irregular  convulsive  movements. — Here,  then,  we 
have  proof  of  the  necessity  of  the  integrity  of  this  ganglionic  centre, 
for  the  possession  of  the  sense  of  vision ;  and  we  have  further  proof, 
that  the  ganglion  is  connected  with  the  muscular  apparatus,  by  motor 
nerves  issuing  from  it.  The  reason  why  the  eye  of  the  opposite  side 
is  affected,  is  to  be  found  in  the  decussation  of  the  optic  nerves; — a 
point  to  be  immediately  adverted  to  (§  910).  The  influence  of  the 
operation  on  the  muscles  of  the  opposite  side  of  the  body,  is  at  once 
understood  from  the  fact  of  the  decussation  of  the  motor  fibres  in  the 
anterior  pyramids  (§  890). 

903.  Thus  we  see,  that  the  Optic  ganglia  receive  the  impressions 
brought  from  the  eyes  by  the  optic  nerves, — convert  them,  as  it  were 
into  sensations, — and  also  transmit  motor  impulses  to  the  muscular 
system,  in  respondence  to  those  sensations.  Thus  they  have  much 
analogy  to  the  cephalic  ganglia  of  the  lower  animals;  the  greater 
part  of  whose  purpose  seems  to  be,  to  guide  the  actions  of  the  beings 
to  which  they  belong,  through  the  sensations  which  they  receive 
(§  860).  But,  with  a  function  that  is  probably  the  same,  there  is  this 
important  difference,  as  to  the  purpose  served  by  these  parts,  in  the 
Encephalon  of  Man,  and  of  the  animals  that  approach  nearest  to  him 
in  the  conformation  of  his  nervous  centres.  The  Consensual  or  In- 
stinctive movements,  which  make  up  nearly  the  whole  of  those  actions 
in  the  Invertebrata  that  are  not  simply  reflex,  constitute  a  compara- 
tively small  proportion  of  the  actions  of  the  higher  Vertebrata  ;  these 
being  guided  in  a  much  greater  degree  by  Intelligence,  w^hich  reasons 
upon  the  sensations,  and  devises  means  to  gratify  the  desires  created 
by  them.  Consequently  there  is  reason  to  think,  that  the  direct  ac- 
tion of  the  sensory  ganglia  upon  the  muscles  is  comparatively  seldom 
exercised,  in  the  active  condition  of  the  Cerebrum.  There  are  certain 
actions,  however,  which  would  seem  to  take  place  regularly  through 
this  channel.  Thus  the  consensual  movements  of  the  eyes,  which 
concur  to  direct  their  axis  towards  the  same  object,  appear  to  depend 
upon  the  impressions  made  upon  the  retinae  ;  for  we  do  not  see  these 
movements  taking  place  with  nearly  the  same  exactness  in  the  eyes 
of  persons  who  have  been  born  totally  blind  ;  and  in  those  who  have 
completely  lost  their  sight,  after  having  enjoyed  the  power  of  vision, 
we  may  always  perceive  that,  although  the  two  eyes  usually  move 
consentaneously  from  habit,  yet  that  their  axes  are  parallel,  instead 
of  convergent;  so  that  they  do  not  seem  to  look  at  any  object,  but 
beyond  it,  into  vacancy. 
33 


514  MUSCULAR  SENSE.— CONSENSUAL  ACTIONS. 

904.  The  existence  of  a  Sensation  of  some  kind,  in  connection 
with  a  Muscular  exertion,  seems  essential  to  the  continuance  of  the 
latter.  Our  ordinary  movements  are  guided  by  what  is  termed  the 
Muscular  Sense  ;  that  is,  by  a  feeling  of  the  condition  of  the  muscle, 
that  comes  to  us  through  its  own  sensory  nerves.  How  necessary 
this  is  to  the  exercise  of  muscular  power,  may  be  best  judged  of  from 
cases  in  which  it  has  been  lost.  Thus  a  woman,  who  had  suffered 
complete  loss  of  sensation  in  one  arm,  but  who  retained  its  motor 
power,  found  that  she  could  not  support  her  infant  upon  it,  without 
constantly  looldng  at  the  child ;  and  that,  if  she  were  to  remove  her 
eyes  for  a  moment,  the  child  would  fall,  in  spite  of  her  knowledge 
that  her  infant  was  resting  upon  her  arm,  and  of  her  desire  to  sustain 
it.  Here,  the  muscular  sense  being  entirely  deficient,  the  sense  of 
vision  supplied  what  was  deficient,  so  long  as  it  was  exercised  upon 
the  object;  but  as  soon  as  this  guiding  influence  was  withdrawn,  the 
strongest  will  could  not  sustain  the  muscular  contraction. — Again,  in 
the  production  of  vocal  sounds,  the  nice  adjustment  of  the  muscles  of 
the  larynx,  which  is  requisite  to  produce  determinate  tones,  can  only 
be  effected  in  obedience  to  a  mental  conception  of  the  tone  to  be 
uttered  ;  and  this  conception  cannot  be  formed,  unless  the  sense  of 
hearing  has  previously  brought  similar  tones  to  the  mind.  Hence  it 
is,  that  persons  who  are  born  deaf^  are  also  dumh.  They  may  have 
no  malformation  of  the  organs  of  speech ;  but  they  are  incapable  of 
uttering  distinct  vocal  sounds  or  musical  tones,  because  they  have 
not  the  guiding  conception,  or  recalled  sensation,  of  the  nature  of 
these.  By  long  training,  and  by  efforts  directed  by  the  muscular 
sense  of  the  larynx  itself,  some  persons  thus  circumstanced  have 
acquired  the  power  of  speech  ;  but  the  want  of  sufficiently  definite 
control  over  the  vocal  muscles,  is  always  very  evident  in  their  use  of 
the  organ. 

905.  Hence,  although  the  proper  consensual  actions  of  Man  and  of 
the  higher  animals  are  comparatively  few,  (the  wants  which  these  are 
destined  to  supply  in  the  lower,  being  in  them  provided  for  by  the 
exercise  of  intelligence,)  we  see  that  not  even  the  proper  voluntary 
movements  can  be  effected,  without  the  influence  of  guiding  sensa- 
tions, felt  or  conceived. — There  are  several  actions,  in  regard  to 
which  it  does  not  seem  easy  to  say  with  certainty,  whether  they  are 
of  a  simply  reflex  nature,  or  whether  sensation  is  a  necessary  link  in 
the  series  of  changes  which  they  involve.  Such  are,  the  act  of  vom- 
iting, produced  by  various  causes  that  excite  nausea, — for  example, 
by  tickling  the  fauces  with  a  feather ;  or  the  acts  of  coughing  and 
sneezing,  excited  by  irritation  in  the  air-passages.  In  regard  to  these 
last  it  may  be  observed,  that  although  the  ordinary  movements  of 
Respiration  are  undoubtedly  of  a  purely  reflex  character,  yet  it  seems 
uncertain,  whether  those  of  an  extraordinary  ndLtnre  can  be  excited  by 
an  impression  that  is  not  felt.  The  act  of  sneezing  is  usually  excited 
by  an  impression  upon  the  5th  pair;  but  it  may  result  from  the  action 
of  a  strong  light  upon  the  eyes,  and  cannot  then  be  excited,  unless 


CONSENSUAL  ACTIONS  IN  MAN.  515 

this  produces  the  sensation  of  dazzling. — There  are  numerous  cases, 
again,  in  which  painful  sensations  appear  to  produce  or  to  modify 
movement,  in  a  manner  that  is  altogether  involuntary.  Thus  in  cases 
of  excessive  irritation  of  the  retina,  rendering  the  eye  most  painfully 
sensitive  to  even  a  feeble  amount  of  light,  the  eyelids  are  drawn 
together  spasmodically  ;  and,  if  they  be  forcibly  opened,  the  pupil  is 
frequently  rolled  beneath  the  upper  lid,  much  farther  than  it  could  be 
carried  by  a  voluntary  effort.  And  in  pleuritis,  pericarditis,  and 
other  painful  affections  of  the  parietes  of  the  chest,  we  may  observe 
the  usual  movements  of  the  ribs  to  be  very  much  abridged  ;  and  if 
the  affection  be  confined  to  one  side,  there  is  a  marked  curtailment 
in  its  movements,  whilst  those  of  the  other  side  may  take  place  as 
usual, — a  difference  which  cannot  be  imitated  by  a  voluntary  effort. 

i906.  Various  other  facts  might  be  adduced,  to  show  that,  in  Man, 
certain  movements  are  as  intimately  and  necessarily  connected  with 
the  excitement  of  sensations  in  the  sensory  ganglia,  as  others  are  with 
the  production  of  impressions  in  the  ganglia  of  reflex  action.  And 
it  maybe  further  questioned,  in  the  absence  of  any  precise  knowledge 
of  the  subject,  w^hether  the  emotions,  when  so  strongly  excited  as  to 
act  involuntarily  on  the  body,  do  not  operate  through  this  group  of 
ganglia  and  the  fibres  proceeding  from  them.  There  are  many  ana- 
logies between  the  purely  emotional  actions  of  Ma>n,  and  the  instinctive 
movements  of  the  lower  animals ;  each  following  closely  upon  sensa- 
tions, without  any  exercise  of  the  reasoning  faculty  ;  and  each  being 
performed,  not  merely  without  the  mandate  of  the  will,  but  often  m 
direct  opposition  to  it.  That  the  Emotions,  when  they  thus  affect  the 
body,  do  not  operate  through  the  same  set  of  nervous  fibres  as  those 
which  convey  the  influence  of  the  Will,  seems  proved  by  this  fa<;t, — 
that  cases  have  occurred,  in  which  muscles  have  been  paralyzed  to 
the  Will,  whilst  they  remained  obedient  to  the  Emotions;  and  vi«e 
versa.  Thus,  in  one  instance,  the  muscles  of  one  side  of  the  face 
were  palsied  in  such  a  manner,  that  the  individual  could  not  volun^- 
tarily  close  his  eye,  nor  draw  his  mouth  towards  that  side;  yet  when 
any  ludicrous  circumstance  caused  him  to  laugh,  their  usual  play  was 
manifested  in  the  expression  of  his  countenance.  And  in  another  case, 
the  muscles  were  obedient  to  the  will ;  but  when  the  individual  laiughed 
or  cried  under  the  influence  of  an  emotion,  it  was  only  on  one  side  of 
his  face.  To  these  may  be  added  another  case,  in  which  the  right 
arm  was  completely  palsied,  so  that  the  individual  had  not  the  least 
voluntary  power  over  it ;  yet  it  was  violently  agitated,  whenever  he 
met  a  friend  whom  he  desired  to  greet. 

907.  These  and  similar  cases  afford  sufficient  proof,  that  the  direct 
influence  of  the  Emotions  on  the  Muscular  System  operates  through 
a  channel  distinct  from  that,  which  conveys  the  influence  of  the  Will ; 
and  when  we  consider  how  closely  the  Emotions  are  connected  with 
the  sensations  which  excite  them,  and  their  close  analogy  with  the 
instincts  of  the  lower  animals,  there  seems  a  strong  presumption  in 
favour  of  the  idea,  that  the  motor  nerves  proceeding  from  the  sensory 


516  CONSENSUAL  ACTIONS  IN  MAN. 

ganglia  constitute  their  peculiar  instrument  of  operation  on  the  body. 
A  very  characteristic  example  of  the  immediate  dependence  of  the 
actions  of  this  class  upon  Sensation,  is  afforded  by  the  peculiar  move- 
ments which  are  excited  by  the  act  of  tickling.  No  one  can  question 
the  completely  involuntary  nature  of  these  movements;  on  the  other 
hand,  they  are  not  reflex^  for  they  do  not  take  place  unless  the  irrita- 
tion is  felt.  They  strictly  belong,  therefore,  to  the  consensual  group 
we  are  at  present  considering.  Now  the  tickling  may  produce,  not 
merely  a  variety  of  semi-convulsive  movements,  tending  to  withdraw 
the  body  from  the  source  of  irritation,  but  also  a  tendency  to  laughter, 
and  an  emotional  state  connected  with  it.  But  it  would  appear  that 
the  semi-convulsive  movements  are  immediately  excited,  not  by  the 
emotion,  but  by  the  sensation.  For  there  is  a  great  variation  amongst 
different  individuals,  as  to  the  results  of  the  irritation;  the  action  of 
laughter  being  excited  in  some,  without  any  other  effect;  whilst  in 
others,  spasmodic  movements  of  the  extremities  take  place  without 
any  tendency  to  laughter,  indeed  with  a  feeling  of  extreme  distress. 

908.  The  influence  of  an  excited  state  of  the  emotional  system  of 
nerves,  is  very  strongly  marked  in  various  disordered  states  of  the 
system ;  and  particularly,  as  already  remarked,  in  Hydrophobia  and 
Hysteria  (§§886,887).  In  both  these  diseases,  violent  convulsive 
paroxysms  are  brought  on,  by  causes  that  produce  particular  sensa- 
tions, or  emotions  consequent  upon  them.  The  tendency  to  imitation 
is  a  most  powerful  cause  in  Hysterical  subjects;  the  mere  sight  of  a 
paroxysm  in  one  young  female,  being  often  sufficient  to  produce  a 
similar  attack  in  a  whole  room-full  of  her  companions.  And  there  are 
some  persons  who  possess  the  powder  of  commanding  an  hysterical 
paroxysm  at  will ;  not  by  voluntarily  executing  the  convulsive  actions 
themselves  ;  but  by  "  getting  up"  the  particular  emotional  condition 
on  W'hich  it  depends.  There  can  be  no  doubt  that  many  of  the  pecu- 
liar movements  exhibited  by  the  subjects  of  Mesmeric  phenomena, 
are  the  result  of  a  condition  of  this  nature.  There  appears  to  be,  in 
such  persons,  an  excessive  activity  of  the  consensual  and  emotional 
system ;  so  that  very  slight  impressions  may  produce  very  powerful 
effects  ;  especially  when  favoured  by  the  strong  desire,  on  the  part  of 
the  patient,  to  exhibit  any  peculiar  manifestation,  that  is  known  to  be 
expected  on  the  part  of  the  bystanders, — a  desire  which  keeps  the 
emotional  system  in  a  state  of  tension,  and  renders  it  peculiarly  respon- 
sive to  any  external  influence. 

909.  Quitting  now  the  functions  of  the  Sensory  ganglia,  w^e  have 
briefly  to  notice  certain  peculiarities  in  the  characters  of  the  nerves 
which  issue  from  them.  And  of  these  peculiarities,  there  is  one  of  a 
very  remarkable  nature,  which  is  common  to  the  three  nerves  oi  special 
sense, — namely,  the  Olfactive,  Optic,  and  Auditory  ; — that  they  are 
not  in  the  least  degree  endowed  with  common  sensibility  ;  so  that  they 
may  be  cut,  stretched,  pinched,  &c.,  without  producing  the  least  pain. 
Consequently,  the  ordinary  sensibility  of  the  surfaces  they  supply  is 
entirelv  due  to  the  branches  of  the  Fifth  pair,  which  are  distributed 


DECUSSATION  OF  THE  OPTIC  NERVES.  517 

upon  them  ;  and  we  may  have  a  loss  of  either  the  general  or  the  special 
sensibility  of  any  of  the  organs  of  sense,  without  the  other  being 
affected,  save  indirectly. — Again,  we  do  not  find  that  irritation  of 
these  nerves  produces  any  other  purely  reflex  movements,  than  such 
as  are  connected  with  the  operations  of  the  organs  of  sense,  in  which 
they  respectively  originate.  Thus  the  Olfactory  nerve  cannot,  by  any 
irritation,  be  made  to  excite  a  reflex  movement ;  the  only  reflex  action 
that  can  be  excited  by  irritating  the  Optic  nerve,  is  contraction  of  the 
Pupil ;  and  the  regulation  of  the  tension  of  the  Membrana  Tympani 
(if,  as  is  probable,  this  is  effected  by  the  motor  power  of  the  Facial 
nerve,  excited  by  impressions  made  upon  the  organ  of  sense,)  appears 
to  be  the  only  reflex  action  to  which  the  Auditory  nerve  can  mi- 
nister. 

910.  There  is  a  further  peculiarity,  of  a  very  marked  kind,  attend- 
ing the  course  of  the  Optic  nerves  ;  this  is  the  crossing  or  decussation 
which  they  undergo,  more  or  less  Completely,  whilst  proceeding  from 
their  ganglia  to  the  eyes.  In  some  of  the  lower  animals,  in  which  the 
two  eyes  (from  their  lateral  position)  have  entirely  different  spheres  of 
vision,  the  decussation  is  complete  ;  the  whole  of  the  fibres  from  the 
right  optic  ganglion  passing  into  the  left  eye,  and  vice  versa.  This  is 
the  case,  for  example,  with  most  of  the  Osseous  Fishes  (as  the  cod, 
halibut,  &c.)  ;  and  also,  in  great  part  at  least,  with  Birds.  In  the 
Human  subject,  however,  and  in  animals  which,  like  him,  have  the 
two  eyes  looking  in  the  same  direction,  the  decussation  seems  less 
complete ;  but  there  is  a  very  remarkable  arrangement  of  the  fibres, 
which  seems  destined  to  bring  the  two  eyes  into  peculianly  consenta- 
neous action.  The  posterior  border  of  the  optic  Chiasma  is  formed 
exclusively  oi  commissural  fibres,  which  pass  from  one  optic  ganglion 
to  the  other,  without  entering  the  real  optic  nerve.  Again,  the  ante- 
rior border  of  the  chiasma  is  composed  of  fibres,  which  seem,  in  like 
manner,  to  act  as  a  commissure  between  the  twore^i??^;  passing  from 
one  to  the  other,  without  any  connection  with  the  optic  ganglia.  The 
tract  which  lies  between  the  two  borders,  and  occupies  the  middle  of 
the  chiasma,  is  the  true  optic  nerve  ;  and  in  this  it  would  appear  that 
a  portion  of  the  fibres  decussates,  whilst  another  portion  passes  directly 
from  each  Optic  ganglion  into  the  corresponding  eye.  The  fibres 
which  proceed  from  the  ganglia  to  the  retinae,  and  constitute  the 
proper  optic  nerves.,  may  be  distinguished  into  an  internal  and  an 
external  tract.  Of  these,  the  external,  on  each  side,  passes  directly 
onwards  to  the  eye  of  that  side  ;  whilst  the  internal  crosses  over  to 
the  eye  of  the  opposite  side.  The  distribution  of  these  two  sets  of 
fibres  in  the  retina  of  each  eye  respectively,  is  such  that,  according 
to  M.  Mayo,  the  fibres  from  either  optic  ganglion  will  be  distributed 
toils  own  side  of  both  eyes; — the  right  optic  ganglion  being  thus 
exclusively  connected  with  the  outer  part  of  the  retina  of  the  right 
eye,  and  with  the  inner  part  of  the  retina  of  the  left  eye  ;  and  the  left 
optic  ganglion  being,  in  like  manner,  connected  exclusively  with  the 
outer  side  of  the  left  retina,  and  with  the  inner  side  of  the  right.    Now 


518  FUNCTIONS  OF  THE  CEREBELLUM. 

as  either  side  of  the  eye  receives  the  images  of  objects,  which  are  on 
the  other  side  of  its  axis,  it  follows,  if  this  account  of  their  distribution  be 
correct,  that  in  Man,  as  in  the  lower  animals,  each  ganglion  receives 
the  sensations  of  objects  situated  on  the  opposite  sides  of  the  body. 
The  purpose  of  this  decussation  may  be,  to  bring  the  visual  impres- 
sions, which  are  so  important  in  directing  the  movements  of  the  body, 
into  proper  harmony  with  the  motor  apparatus ;  so  that,  the  decussa- 
tion of  the  motor  fibres  in  the  pyramids  being  accompanied  by  a 
decussation  of  the  optic  nerves,  the  same  effect  is  produced  as  if 
neither  decussated, — which  last  is  the  case  with  Invertebrated  ani- 
mals in  general. 

6.  Functions  of  the  Cerebellum. 

911.  Much  discussion  has  taken  place,  of  late  years,  respecting  the 
uses  of  the  Cerebellum  ;  and  many  experiments  have  been  made  to 
determine  them.  That  it  is  in  some  way  connected  with  the  powers 
of  motion^  might  be  inferred  from  its  connection  with  the  antero- 
lateral columns  of  the  Spinal  Cord,  as  well  as  with  the  posterior;  and 
the  comparative  size  of  the  organ,  in  different  orders  of  Vertebrated 
animals,  gives  us  some  indication  of  what  the  nature  of  its  function 
may  be.  For  we  find  its  degree  of  development  corresponding  pretty 
closely  with  the  variety  and  energy  of  the  muscular  movements  which 
are  habitually  executed  by  the  species;  the  organ  being  the  largest 
in  those  animals,  which  require  the  combined  effort  of  a  great  variety 
of  muscles  to  maintain  their  usual  position,  or  to  execute  their  ordi- 
nary movements ;  whilst  it  is  the  smallest  in  those,  which  require  no 
muscular  exertion  for  the  one  purpose,  and  little  combination  of  dif- 
ferent actions  for  the  "other.  Thus  in  animals  that  habitually  rest  and 
move  upon  four  legs,  there  is  comparatively  little  occasion  for  any 
organ  to  combine  and  harmonize  the  actions  of  their  several  muscles; 
and  in  these,  the  Cerebellum  is  usually  small.  But  among  the  more 
active  predaceous  Fishes  (as  the  Shark), — Birds  of  the  most  pow^erful 
and  varied  flight  (as  the  Swallow), — and  such  Mammals  as  can  main- 
tain the  erect  position,  and  can  use  their  extremities  for  other  purposes 
than  support  and  motion, — we  find  the  Cerebellum  of  much  greater 
size,  relatively  to  the  remainder  of  the  Encephalon.  There  is  a 
marked  advance  in  this  respect,  as  we  ascend  through  the  series  of 
Quadrumanous  animals  ;  from  the  Baboons,  which  usually  w^alk  on 
all-fours,  to  the  semi-erect  Apes,  which  often  stand  and  move  on 
their  hind-legs  only.  The  greatest  development  of  the  Cerebellum  is 
found  in  Man ;  who  surpasses  all  other  animals  in  the  number  and 
variety  of  the  combinations  of  muscular  movement,  which  his  ordi- 
nary actions  involve,  as  well  as  of  those  which  he  is  capable,  by 
practice,  of  learning  to  execute. 

912.  From  experiments  upon  all  classes  of  Vertebrated  animals,  it 
has  been  found  that,  when  the  Cerebellum  is  removed,  the  power  of 
walking,  springing,  flying,  standing,  or  maintaining  the  equilibrium 
of  the  body,  is  destroyed.     It  does  not  seem  that  the  animal  has  in 


REGULATION  OF  MOVEMENTS.  519 

any  degree  lost  the  voluntarypovfer  over  its  individual  muscles;  but 
it  cannot  combine  their  actions  for  any  general  movements  of  the  body. 
The  reflex  movements,  such  as  those  of  respiration,  remain  unim- 
paired. When  an  animal  thus  mutilated,  is  laid  on  its  back,  it 
cannot  recover  its  former  posture  ;  but  it  moves  its  limbs,  or  flutters  its 
wings,  and  evidently  is  not  in  a  state  of  stupor.  When  placed  in  the 
erect  position,  it  staggers  and  falls  like  a  drunken  man, — not,  however, 
without  making  efforts  to  maintain  its  balance.  Phrenologists,  who 
attribute  a  different  function  to  the  Cerebellum,  have  attempted  to  put 
aside  these  results,  on  the  ground  that  the  severity  of  the  operation 
is  alone  sufficient  to  produce  them;  but  as  we  shall  presently  see, 
many  animals  may  be  subjected  to  a  much  more  severe  operation, — 
the  removal  of  the  Cerebral  hemispheres, — without  the  loss  of  the 
power  of  combining  and  harmonizing  the  muscular  actions,  provided 
the  Cerebellum  be  left  uninjured. — Thus,  then,  the  idea  of  the  func- 
tions of  the  Cerebellum,  which  we  derive  from  Comparative  Anatomy, 
seems  fully  borne  out  by  the  results  of  experiment ;  and  it  is  also 
consistent  with  the  indications,  which  may  be  drawn  from  the  obser- 
vations of  Pathological  phenomena.  When  the  Cerebellum  is  affected 
with  chronic  disease,  the  motor  function  is  seldom  destroyed ;  but 
the  same  kind  of  want  of  combining  power  shows  itself,  as  when  the 
organ  has  been  purposely  mutilated.  Some  kind  of  lesion  of  the 
motor  function  is  invariably  to  be  observed  ;  whilst  the  mental  powers 
may  or  may  not  be  affected, — probably  according  to  the  influence  of 
the  disease  in  the  Cerebellum  upon  other  parts.  The  same  absence 
of  any  direct  connection  with  the  Psychical  powers,  is  shown  in  the 
fact,  that  inflammation  of  the  membranes  covering  it,  if  confined  to 
the  Cerebellum,  does  not  produce  delirium.  Sudden  effusions  of 
blood  into  its  substance  may  produce  apoplexy  or  paralysis ;  but  this 
may  occur  as  a  consequence  of  effusions  into  any  part  of  the  Ence- 
phalon,  and  does  not  indicate,  that  the  Cerebellum  has  anything  to 
do  with  the  mental  functions,  or  with  the  power  of  the  Will  over  the 
muscles. 

913.  There  is  another  doctrine,  however,  in  regard  to  the  functions 
of  the  Cerebellum,  first  propounded  by  Gall;  which  ought  not  to  be 
altogether  passed  by.  According  to  the  system  of  Phrenologists,  the 
Cerebellum  is  the  organ  of  the  sexual  instinct ;  and  its  connection  with 
the  motor  function  is  limited  to  the  performance  of  the  movements,  to 
which  that  instinct  leads.  This  doctrine  derives  no  support,  however, 
from  the  facts  supplied  by  Comparative  Anatomy ;  for  there  is  a  com- 
plete want  of  correspondence  between  the  size  of  the  Cerebellum  in 
different  animals,  and  the  power  of  their  sexual  instinct. — Again, 
although  pathology  has  been  appealed  to,  as  showing  a  decided  con- 
nection between  disease  of  the  Cerebellum  and  affection  of  the  Genital 
organs,  (manifesting  itself  in  priapism,  turgescence  of  the  testes,  seminal 
emissions,  &c.,)  yet  it  appears,  on  a  careful  examination  of  evidence 
that  such  a  sympathy  is  comparatively  rare,  not  being  displayed  in 
more  than  one  out  of  every  seventeen  cases  of  Cerebellic  disease.  And 


520  SEXUAL  INSTINCT.— FUNCTIONS  OF  THE  CEREBRUM. 

where  it  is  manifested,  it  is  explicable  quite  readily  by  the  known 
fact  that  this  kind  of  excitement  of  the  genital  organs  may  be  pro- 
duced by  excitement  of  the  spinal  cord  and  medulla  oblongata. — Little 
or  no  light  has  been  thrown  on  this  question  by  experiment.  It  was 
asserted  by  Gall,  that  the  Cerebellum  is  very  small  in  castrated  ani- 
mals; but  this  assertion  has  been  met  by  the  most  positive  counter- 
statements  on  the  part  of  Leuret,  who  has  shown  that  the  average 
weight  of  the  Cerebellum  (both  absolutely,  and  in  proportion  to  the 
weight  of  the  entire  encephalon),  is  even  greater  in  Geldings  than  in 
Stallions  or  Mares. — It  is  asserted,  however,  that  the  results  of  ob- 
servation in  Man  lead  to  a  positive  conclusion,  that  the  size  of  the 
Cerebellum  is  a  measure  of  the  intensity  of  the  sexual  instinct  in  the 
individual.  This  assertion  has  been  met  by  the  counter-statement  of 
others, — that  no  such  relation  exists.  There  are,  of  course,  very 
great  difficulties  in  regard  to  the  collection  of  accurate  information  on 
this  subject;  and  the  question  must  be  at  present  regarded  as  sub 
judice. 

914.  It  may  be  added,  that  the  idea  of  a  special  connection  between 
the  sexual  instinct  and  the  Cerebellum,  is  not  inconsistent  with  the 
view  of  its  function  previously  stated ;  and  it  would  seem  to  derive 
some  confirmation  from  the  fact  that  an  unusual  amount  of  muscular 
exertion  appears  to  have  a  peculiar  tendency  to  depress  the  sexual 
passion  even  whilst  it  increases  the  general  vigour  of  the  system.  If 
the  Cerebellum  be  really  connected  with  both  kinds  of  functions,  it 
does  not  seem  unlikely  that  the  excessive  employment  of  it  upon  one, 
should  diminish  its  energy  in  regard  to  the  other.  Further,  it  seems 
not  improbable  that  the  Lobes  of  the  Cerebellum  are  the  parts  spe- 
cially concerned  in  the  regulation  of  the  muscular  movements  ;  whilst 
the  central  portion  (constituting  the  Vermiform  process  in  Man,  but 
forming  the  entire  cerebellum  of  many  of  the  lower  Vertebrata,  such 
as  the  Frog),  may  be  the  centre  of  the  sexual  sensations,  and  the 
instrument  of  the  consensual  actions  to  which  they  give  rise. 

7.  Functions  of  the  Cerebrum. 

915.  The  view  which  has  been  taken  of  the  Comparative  structure 
of  the  Nervous  system,  in  different  animals,  leads  to  the  conclusion, 
that  the  Cerebral  hemispheres  are  far  from  being  the  essential  parts 
of  the  apparatus  they  were  formerly  imagined  to  be  ;  and  that  they  are 
on  the  contrary,  superadded  organs,  of  which  we  find  no  distinct  re- 
presentatives in  the  Invertebrata,  and  of  w^hich  the  first  appearance 
(in  the  class  of  Fishes)  exhibits  them  in  the  light  of  appendages,  de- 
stined to  perform  some  special  function  peculiar  to  Vertebrated  animals. 
The  results  of  the  removal  of  the  Cerebral  Hemispheres,  in  animals  to 
which  the  shock  of  the  operation  does  not  prove  immediately  fatal, 
fully  confirm  this  view  ;  and  must  appear  extraordinary  to  those,  who 
have  been  accustomed  to  regard  these  organs  as  the  centre  of  all  en- 
ergy.    Not  only  Reptiles,  but  Birds  and  Mammalia,  if  their  physical 


RELATIVE  DEVELOPMENT  OF  THE  CEREBRUM.       521 

wants  be  supplied,  may  survive  the  removal  of  the  whole  Cerebrum 
for  weeks,  or  even  months.  If  the  entire  mass  be  taken  away  at  once, 
the  operation  is  usually  fatal ;  but  if  it  be  removed  by  successive 
slices,  the  shock  is  less  severe,  and  the  depression  it  produces  in  the 
organic  functions  is  soon  recovered  from.  It  is  difficult  to  substantiate 
the  existence  of  actual  sensation,  in  animals  thus  circumstanced  ;  but 
their  movements  appear  to  be  of  a  higher  kind  than  those  resulting 
from  mere  reflex  action.  Thus  they  will  eat  food  when  it  is  put  into 
their  mouths;  although  they  do  not  go  to  seek  it.  One  of  the  most 
remarkable  phenomena  of  such  beings,  is  their  power  of  maintaining 
their  equilibrium ;  which  could  scarcely  exist  without  consciousness. 
If  a  Rabbit,  thus  mutilated,  be  laid  upon  its  back,  it  rises  again  ;  if 
pushed,  it  walks;  if  a  Bird  be  thrown  into  the  air,  it  flies ;  if  a  Frog 
be  touched,  it  leaps.  If  violently  aroused,  the  animal  has  all  the 
manner  of  one  waking  from  sleep ;  and  it  manifests  about  the  same 
degree  of  consciousness  as  a  sleeping  Man,  whose  torpor  is  not  too 
profound  to  prevent  his  suffering  from  an  uneasy  position,  and  who 
moves  himself  to  amend  it.  In  both  cases,  the  movements  are  con- 
sensual only,  and  do  not  indicate  any  voluntary  power ;  and  we  may 
well  believe  that,  in  the  former  case  as  in  the  latter,  though  felt,  they 
are  not  remembered;  an  active  state  of  the  Cerebrum  being  essential 
to  memory,  though  not  to  sensations,  which  simply  excite  certain 
actions. 

916.  As  already  stated,  the  relative  amount  of  Intelligence  in  dif- 
ferent animals  bears  so  close  a  correspondence  with  the  relative  size 
and  development  of  the  Cerebral  Hemispheres,  that  it  can  scarcely  be 
questioned  that  these  constitute  the  organ  of  the  Reasoning  faculties, 
and  issue  the  mandates  by  which  the  Will  calls  the  muscles  into 
action.  It  must  be  borne  in  mind,  however,  that  size  is  not  by  any 
means  the  only  indication  of  their  comparative  development.  As  we 
advance  from  the  lower  to  the  higher  Vertebrata,  we  observe  a  marked 
advance  in  the  complexity  of  the  structure  of  the  Cerebrum.  Its  surface 
becomes  marked  by  convolutions,  that  greatly  increase  the  area  over 
which  blood-vessels  can  enter  it  from  the  surrounding  membranes ; 
and  in  proportion  to  the  increase  in  the  number  and  depth  of  these,  do 
we  find  an  increase  in  the  thickness  of  the  layer  of  gray  matter,  which 
is  the  source  of  all  the  powers  of  the  organ.  The  arrangement  of  the 
white  or  fibrous  tissue,  which  forms  the  interior  of  the  mass,  also  in- 
creases in  complexity ;  and  as  we  ascend  even  from  the  lower  Mam- 
malia up  to  Man,  we  trace  a  marked  increase  in  the  number  of  the 
fibres,  which  establish  communications  between  different  parts  of  the 
organ.  It  is,  in  fact,  not  merely  from  the  different  parts  of  the  gray 
matter,  which  forms  the  surface  of  the  hemispheres,  that  these  com- 
missural fibres  arise ;  but  also  from  those  isolated  portions  of  vesicular 
substance,  which  are  found  in  different  parts  of  their  interior  ;  and  an 
extremely  complex  system  is  thus  formed,  which  is  still  but  very  im- 
perfectly understood. 

917.  The  two  hemispheres  are  united  on  the  median  line  by  several 


522  COMMISSURES  OF  THE  CEREBRAL  HEMISPHERES. 

transverse  Commissures;  of  which  the  Corpus  Callosum  is  the  most 
important.  This  consists  of  a  mass  of  fibres  very  closely  interlaced 
together ;  which  may  be  traced  into  the  substance  of  the  hemispheres 
on  each  side,  particularly  at  their  lower  part,  where  they  are  connected 
with  the  thalami  optici  and  corpora  striata.  It  is  difficult,  if  not  im- 
possible, to  trace  its  fibres  any  further ;  but  there  can  be  little  doubt 
that  they  radiate,  with  the  fibres  proceeding  from  the  bodiesjust  named, 
to  the  different  parts  of  the  surface  of  the  hemispheres.  This  commis- 
sure is  altogether  absent  in  Fish,  Reptiles,  and  Birds ;  and  it  is  par- 
tially or  completely  wanting  in  the  Mammalia  with  least  perfect 
brains, — as  the  Rodents  and  Marsupials. — The  anterior  commissure 

Fig.  145. 


The  mesial  surface  of  a  longitudinal  section  of  the  brain.  The  incision  has  been  carried  along  the 
middle  line  ;  between  the  two  hemispheres  of  the  cerebrum,  and  through  the  middle  of  the  cerebellum 
and  medulla  oblongata.  1.  Tlie  inner  surface  of  ihe  left  hemisphere.  2.  The  divided  surface  of  the 
cerebellum,  showing  the  arbor  vitfe.  3.  The  medulla  oblongata.  4.  The  corpus  callosum.  curving 
downwards  in  front  to  terminate  at  the  base  of  the  brain;  and  rounded  behind,  to  become  continuous 
with  5,  the  fornix.  6.  One  of  the  crura  of  the  tbrnix  descending  to  7,  one  of  the  corpora  albicantia.  8. 
The  septum  lucidum.  9.  The  velum  interpositum,  communicating  with  the  pia  mater  of  the  convolu- 
tions through  the  fissure  of  Bicha.t.  10.  Section  of  the  middle  commissure  situated  in  the  third  ven- 
tricle. 11  "Section  of  the  anterior  commissure.  12.  Section  of  the  posterior  commissure  ;  the  commis- 
sure is  somewhat  above  and  to  the  left  of  the  numeral.  The  interspace  between  10  and  11  is  the 
foramen  commune  anterius,  in  which  the  crus  of  the  fornix  (6)  is  situated.  The  interspace  between  10 
and  12  is  the  foramen  commune  posterius.  13.  The  corpora  quadrigemina,  upon  which  is  seen  resting 
the  pineal  gland,  14.  15.  The  iter  a  tertio  ad  quarlum  ventriculum,  or  aqueduct  of  Sylvius.  16.  The 
fourth  ventricle.  17.  The  pons  Varolii,  through  which  are  seen  passing  the  diverging  fibres  of  the 
corpora  pyramidalia.  18.  The  crus  cerebri  of  the  left  side,  with  the  third  nerve  arising  from  it.  19. 
The  tuber  cinereum,  from  which  projects  the  infundibulum,  having  the  pituitary  gland  appended  to  its 
extremity.  20.  One  of  the  optic  nerves.  21.  The  left  olfactory  nerve  terminating  anteriorly  in  a 
rounded  bulb. 

particularly  unites  the  corpora  striata  of  the  two  sides ;  but  many  of 
its  fibres  pass  through  those  organs,  and  radiate  towards  the  convolu- 
tions of  the  hemispheres,  especially  those  of  the  middle  lobe.  This 
commissure  is  particularly  large  in  those  Marsupials,  in  which  the 
Corpus  Callosum  is  deficient. — The  posterior  commissure  is  a  band  of 
fibres  which  connects  the  optic  thalami;  crossing  over  from  the  poste- 
rior extremity  of  one  to  that  of  the  other. — Besides  these,  there  are 
other  groups  of  fibres,  which  seem  to  have  similar  commissural  func- 
tions, but  which  are  intermingled  with  vesicular  substance.  Such  are 
the  soft  commissure,  which  also  extends  between  the  thalami ;  the 
Pons  Tarini,  which  extends  between  the  two  crura  or  peduncles  of 
the  cerebrum ;  and  the  Tuber  cinereum,  which  seems  to  unite  the 


FUNCTIONS  OF  THE  CEREBRUM.  523 

optic  tracts  with  the  thalami,  the  corpus  callosum,  the  fornix,  &c., 
and  to  be  a  common  point  of  meeting  for  several  distinct  groups  of 
fibres. 

918.  The  anterior  and  posterior  parts  of  the  hemispheres,  more- 
over, are  connected  by  Ivngifudinal  Commissures;  of  which  some  lie 
above,  and  some  below,  the  corpus  callosum.  Above  the  transverse 
fibres  of  the  corpus  callosum,  there  is  a  longitudinal  tract  on  each  side 
of  the  median  line,  w^hich  serves  to  connect  the  convolutions  of  the 
anterior  and  posterior  lobes  of  the  brain. — And  above  this,  again,  is 
the  superior  longitudinal  commissure,  which  is  formed  by  the  fibrous 
matter  of  the  great  convolution  nearest  the  median  plane  on  the  up- 
per surface  of  the  brain,  and  which  connects  the  convolutions  of  the 
anterior  and  middle  lobe  with  those  of  the  posterior. — Beneath  the 
great  transverse  commissure,  we  find  the  most  extensive  of  all  the 
longitudinal  commissures,  namely,  the  fornix.  This  is  connected  in 
front  with  the  optic  thalami,  the  raammillary  bodies,  the  tuber  cine- 
reum,  &c.;  and  behind,  it  spreads  its  fibres  over  the  hippocampi  (major 
and  minor),  which  are  nothing  else  than  peculiar  convolutions  that 
project  into  the  posterior  and  descending  cornua  of  the  lateral  ventri- 
cles.— The  fourth  longitudinal  commissure  is  the  tceniasemicircularis, 
which  forms  part  of  the  same  system  of  fibres  with  the  fornix  ;  con- 
necting the  corpus  mammilare  and  thalamus  opticus  with  the  middle 
lobe  of  the  cerebral  hemisphere. — If,  as  Dr.  Todd  has  remarked,  we 
could  take  away  the  corpus  callosum,  the  gray  matter  of  the  internal 
convolution,  and  the  ventricular  prominence  of  the  optic  thalami,  then 
all  these  commissures  falltogether,  and  become  united  as  one  and  the 
same  series  of  longitudinal  fibres. 

919.  Besides  these,  it  is  probable  that  the  different  convolutions 
have  their  own  commissural  fibres  uniting  them  with  each  other,  as 
well  as  their  radiating  fibres  connecting  them  with  the  thalami  optici 
and  corpora  striata  ;  but  these  have  not  been  certainly  demonstrated. 
It  is  curious  that  there  should  be  no  direct  communication  between 
the  Cerebral  hemispheres  and  the  Cerebellum  ;  the  only  commissural 
band  between  them  being  the  processus  a  cerebello  ad  testes,  w^hich 
passes  onwards,  through  the  tubercula  quadrigemina,  to  the  thalamus 
opticus  on  each  side.  This  would  seem  to  confirm  the  idea  of  the 
complete  distinctness  of  their  functions. 

920.  Very  little  light  can  be  thrown  by  experiment  upon  the  func- 
tions of  the  several  parts  of  the  Cerebral  hemispheres,  or  of  the  gan- 
glionic masses  with  w^hich  they  are  so  intimately  connected.  In  the 
experiments  already  referred  to,  in  which  the  hemispheres  were  en- 
tirely removed,  slice  by  slice,  it  was  noticed  that  injuries  of  these 
organs  neither  occasion  any  signs  of  pain,  nor  give  rise  to  convulsive 
movements.  Even  the  thalami  and  corpora  striata  may  be  wounded, 
without  the  excitement  of  convulsions ;  whilst,  if  the  incisions  involve 
the  tubercula  quadrigemina,  convulsions  uniformly  occur.  It  has  been 
often  observed  in  Man,  that,  w^hen  it  has  been  necessary  to  separate 
protruded  portions  of  the  brain  from  the  healthy  part,  no  sensation 


524  SLEEP;    COMA. 

was  produced,  even  though  the  mind  was  perfectly  clear  at  the  time. 
Hence  it  would  appear  that  neither  is  the  Cerebrum  itself  the  centre 
of  sensation,  nor  is  it  so  connected  with  that  centre,  as  to  be  able  to 
convey  to  it  sensory  impressions  of  an  ordinary  kind.  This  is  analo- 
gous to  the  condition  of  tl^e  nerves  of  special  sense,  as  already  re- 
marked. That  no  irritation  of  the  cerebral  substance  should  excite 
convulsive  movements,  is  a  very  remarkable  circumstance;  and  it 
seems  to  indicate,  that  the  changes  which  mental  operations  produce 
in  the  cerebral  fibres,  cannot  be  imitated,  as  changes  in  other  motor 
fibres  may  be,  by  physical  impressions. 

921.  There  are  various  conditions,  some  of  them  natural,  others 
morbid,  in  which  the  distinctness  of  the  functions  of  the  Cerebral  He- 
mispheres is  well  marked.  Thus  in  profound  sleep,  they  seem  to  be 
entirely  dormant ;  the  Spinal  system,  by  which  the  necessary  reflex 
actions  are  carried  on,  being  alone  in  a  state  of  activity.  In  this  con- 
dition, the  Sensory  ganglia  also  appear  to  be  in  a  torpid  state  ;  but  in 
less  profound  sleep,  actions  are  often  performed,  which  maybe  referred 
to  the  consensual  group, — being  such  as  the  sensation  would  imme- 
diately prompt,  without  any  reflection,  and  not  being  remembered  in 
the  waking  state.  Thus  we  turn  in  our  beds,  under  the  influence  of 
an  uneasy  sensation  ;  or  we  give  some  sign  of  recognition  when  our 
names  are  called.  The  first  of  these  appears  to  be  a  purely  consen- 
sual movement,  being  as  automatic  as  if  it  were  a  reflex  action  ;  the 
other  seems  to  have  become  as  automatic,  by  the  influence  of  habit, 
and  to  belong  to  that  class,  in  which  the  mind  was  at  first  involved, 
but  in  which,  after  very  frequent  performance,  the  sensation  suggests 
the  action  so  immediately  and  invariably,  that  the  action  seems  to  take 
place  without  any  concern  on  the  part  of  the  will.  Of  these  secondary 
automatic  actions,  as  they  are  termed,  we  have  many  examples  in  that 
condition,  in  which  the  mind,  though  active,  is  so  completely  absorbed 
by  some  train  of  thought,  as  to  be  in  a  state  of  revery^  and  to  be  in- 
sensible to  external  objects  ;  in  such  a  condition,  the  individual  may 
continue  reading  aloud,  playing  a  piece  of  music,  or  performing  any 
other  action,  in  which  the  muscular  movements  are  immediately 
directed  by  the  sensations  ;  but  he  cannot  carry  on  two  distinct  and 
independent  trains  of  thought. 

922.  In  the  Coma  of  Apoplexy,  Narcotic  Poisoning,  &c.,  we  wit- 
ness the  same  gradations  as  in  ordinary  sleep.  When  it  is  least  pro- 
found, it  seems  to  affect  the  Cerebral  hemispheres  alone  ;  the  Sensory 
Ganglia  being  still,  in  some  degree,  open  to  the  reception  of  impres- 
sions. When  complete,  however,  none  but  reflex  actions  can  be 
excited  ;  and  if  it  advance  to  a  fatal  termination,  it  does  so  by  the 
supervention  of  the  same  state  of  torpidity  in  the  Medulla  Oblongata, 
whereby  the  respiratory  movements  are  brought  to  a  close.  These 
movements  do  not  cease  until  the  power  of  deglutition  has  been  lost, 
and  until  the  eye  ceases  to  close  when  the  edge  of  the  lid  is  irritated  ; 
but  when  this  is  the  case,  a  fatal  termination  may  be  apprehended,  as 


SOMNAMBULISM;    MEMORY.  525 

it  is  thus  shown  that  the  torpor  is  extending  to  the  Spinal  system  of 
nerves. 

923.  In  the  condition  of  Dreaming,  it  would  seem  as  if  the  Cere- 
brum were  partially  active;  a  train  of  thought  being  suggested,  fre- 
quently by  sensations  from  without ;  which  is  carried  on  without  any 
controlling  or  directing  power  on  the  part  of  the  Mind  ;  and  which  is 
not  corrected,  or  is  only  modified  in  a  limited  degree,  by  the  know- 
ledge acquired  by  experience.  This  condition  is  still  more  remarkable 
in  Somnambulism,  or  (as  it  has  been  better  termed)  Sleep- waking  ;  on 
which  the  dreams  are  not  only  aded^  but  may  be  often  acted  on  with 
the  utmost  facility, — a  suggestion  conveyed  through  any  of  the  senses 
excepting  sight  (which  is  usually  in  abeyance)  being  apprehended  and 
followed  up  with  the  utmost  readiness,  and,  in  like  manner,  with  little 
or  no  correction  from  experience.  Between  this  condition,  and  that 
of  ordinary  dreaming,  on  the  one  hand,  and  that  of  complete  insensi- 
bility on  the  other,  there  is  every  shade  of  variety;  which  is  presented 
by  different  individuals,  or  by  the  same  individuals  at  different  times. 
The  Cerebellum,  in  the  Sleep-waking  state,  seems  to  be  frequently  in 
a  condition  of  peculiar  activity;  remarkable  power  of  balancing  and 
combining  the  movements  of  the  body,  being  often  exhibited. 

924.  The  faculty  of  Memory  appears  to  be  the  exclusive  attribute 
of  the  Cerebral  hemispheres;  no  impressions  made  upon  the  Organs  of 
Sense  being  ever  remembered,  unless  they  are  at  once  registered  (as  it 
were)  in  this  part  of  the  nervous  centres.  This  faculty  is  one  of  those 
first  awakened  in  the  opening  mind  of  the  Infant;  and  it  is  one  of 
which  we  find  traces  in  animals,  that  seem  to  be  otherwise  governed 
by  pure  Instinct.  It  obviously  affords  the  first  step  towards  the  exer- 
cise of  the  reasoning  powers ;  since  no  experience  can  be  obtained 
without  it;  and  the  foundation  of  all  intelligent  adaptation  of  means 
to  ends,  lies  in  the  application  of  the  knowledge  which  has  been 
acquired,  and  stored  up  in  the  mind.  There  is  strong  reason  to 
believe,  that  no  impression  of  this  kind,  once  made  upon  the  Brain, 
is  ever  entirely  lost, — except  through  disease  or  accident,  which  will 
frequently  destroy  the  memory  altogether,  or  will  annihilate  the  recol- 
lection of  some  particular  class  of  objects  or  of  words.  All  memory, 
however,  seems  to  depend  upon  the  principle  of  Association  ;  one  idea 
being  linked  with  another,  or  w^th  a  particular  sensation,  in  such  a 
manner  as  to  be  called  up  by  its  recurrence;  and  a  period  of  many 
years  frequently  intervening,  without  the  combination  of  circumstances 
presenting  itself,  which  is  requisite  to  arouse  the  dormant  impression 
of  some  early  event.  Sometimes  this  combination  occurs  in  dreaming, 
delirium,  or  insanity;  and  ideas  are  recalled,  of  which  the  mind,  in  a 
state  of  healthy  activity,  has  no  remembrance. 

925.  Although  there  does  not  seem  any  improbability  in  the  suppo- 
sition, that  different  faculties  of  the  mind  should  have  different  parts 
of  the  Cerebral  hemispheres  as  their  special  instruments,  yet  suflScient 
evidence  of  the  correctness  of  the  (so-called)  Phrenological  distribu- 
tion of  organs,  has  not  yet,  in  the  Author's  opinion,  been  adduced,  to 


526  FUNCTIONS  OF  THE  SYMPATHETIC  SYSTEM. 

justify  its  admission  into  an  Elementary  Treatise  like  the  present;  and 
the  subject  will  therefore  be  passed  by. 

8.  Functions  of  the  Sympathetic  System. 

926.  The  Cerebro-Spinal  apparatus,  of  which  the  several  parts  have 
now  been  described,  is  not  the  only  system  of  ganglia  and  nerve- 
trunks,  that  is  contained  within  the  body  of  a  Vertebrated  animal. 
There  is  another  system,  having  its  own  set  of  centres,  and  its  own 
distribution  of  branches;  characterized  also*  by  a  peculiarity  in  the 
nature  of  the  nervous  fibres,  of  which  its  trunks  are  composed  ;  and 
communicating  at  numerous  points  with  the  preceding.  It  will  be 
remembered  that,  in  front  of  the  vertebral  column,  there  is  a  series 
of  ganglia  on  each  side  ;  communicating,  on  the  one  hand,  with  the 
spinal  nerves,  as  they  issue  from  the< vertebral  canal;  and  also  con- 
necting themselves  with  the  two  large  semilunar  ganglia,  which  lie 
amidst  the  abdominal  viscera  ;  as  well  as  with  a  series  of  ganglia,  that 
is  found  near  the  base  of  the  heart.  In  the  head,  also,  there  are 
numerous  scattered  ganglia,  which  evidently  belong  to  the  same 
system;  having  numerous  communications  with  the  cephalic  nerves; 
and  being  also  connected  with  the  chain  of  ganglia  in  the  neck.  The 
branches  proceeding  from  this  series  of  ganglia  are  distributed,  not  to 
the  skin  and  muscles  (like  those  of  the  cerebro-spinal  system),  but  to 
the  organs  of  digestion  and  secretion,  to  the  heart  and  lungs,  and 
particularly  to  the  walls  of  the  blood-vessels,  on  which  they  form  a 
plexus,  whose  branches  probably  accompany  their  minutest  ramifica- 
tions. The  peculiar  connection  of  this  system  of  nerves  with  the 
organs  of  vegetative  life,  has  caused  it  to  receive  the  designation  of 
the  Nervous  System  of  Organic  Life  ;  the  Cerebro-Spinal  system  being 
termed  the  Nervous  System  of  Animal  Life.  It  is  also  not  unfre- 
quently  termed  the  ganglionic  system;  on  account  of  the  separation 
of  its  centres  into  scattered  ganglia,  which  forms  a  striking  contrast 
to  the  concentration  that  is  so  evident  in  the  Cerebro-Spinal  system. 
But  this  term  is  objectionable,  as  leading  to  a  supposed  analogy 
between  this  system  and  the  general  nervous  system  of  Invertebrata, 
whose  centres  are  equally  scattered  ; — an  analogy  which  is  completely 
erroneous,  since,  as  we  have  seen,  this  last  is  chiefly  the  representative 
of  the  Cerebro-Spinal  system  of  Vertebpted  animals.  The  term 
Sympathetic  is,  perhaps,  the  best;  although  it  must  not  be  supposed 
that  the  system  of  nerves  is  the  instrument  of  by  any  means  all  the 
sympathies,  which  manifest  themselves  between  different  organs. 

927.  The  Sympathetic  system  contains  two  classes  of  nervous 
fibres ; — the  ordinary  white  tubular  fibres,  all  of  which  are  probably 
derived  from  the  Cerebro-Spinal  system  ;  and  the  gray  or  gelatinous 
fibres,  which  seem  to  belong  exclusively  to  itself  (§  375).  True  it 
is,  that  some  of  these  last  are  found  in  the  spinal  nerves ;  but  they 
seem,  even  there,  to  form  part  of  the  Sympathetic  system, — their 
centres  being  the  ganglia  on  the  posterior  roots  of  the  Spinal  nerves, 


FUNCTIONS  OF  THE  SYMPATHETIC  SYSTEM.  527 

which  communicate  with  the  true  Sympathetic  ganglia,  and  which 
seem  to  form  a  part  of  the  same  series.  Thus  we  may  consider  each 
system  as  intermingling  itself  with  the  other; — the  Cerebro-spinal 
system  transmitting  some  of  its  fibres,  both  motor  and  sensory,  into 
the  Sympathetic  ; — whilst  the  Sympathetic  is  represented  in  the  Cere- 
bro-Spinal  system,  by  certain  fibres  and  collections  of  vesicular  mat- 
ter of  its  own.  The  trunks  that  proceed  from  the  Semilunar  ganglia, 
are  almost  entirely  composed  of  gray  or  organic  fibres ;  whence  it  is 
evident  that  these  ganglia  are  to  be  regarded  as  the  true  centres  of 
the  Sympathetic  system.  On  the  other  hand,  the  trunks  which  issue 
from  the  chain  of  spinal  ganglia,  contain  a  large  admixture  of  white 
or  tubular  fibres. 

928.  The  Sympathetic  nerves  possess  a  certain  degree  of  power  of 
exciting  Muscular  contractions,  in  the  various  parts  to  which  they 
are  distributed.  Thus  by  irritating  them,  immediately  after  the  death 
of  an  animal,  contractions  may  be  excited  in  any  part  of  the  aliment- 
ary canal,  from  the  pharynx  to  the  rectum,  according  to  the  trunks 
which  are  irritated, — in  the  heart,  after  its  ordinary  movements  have 
ceased, — in  the  aorta,  vena  cava,  and  thoracic  duct, — in  the  ductus 
choledochus,  uterus,  Fallopian  tubes,  vas  deferens,  and  vesiculee  semi- 
nales.  But  the  very  same  contractions  may  be  excited,  by  irritating 
the  roots  of  the  Spinal  nerves,  from  w^hich  the  Sympathetic  trunks 
receive  their  white  fibres ;  and  there  is,  consequently,  strong  reason 
to  believe  that  the  motor  power  of  the  latter  is  entirely  dependent 
upon  the  Cerebro-spinal  system.  Whatever  sensory  endowments  the 
Sympathetic  trunks  possess,  are  probably  to  be  referred  to  the  same 
connection.  In  the  ordinary  condition  of  the  body,  these  are  not 
manifested.  The  parts  exclusively  supplied  by  Sympathetic  trunks 
do  not  appear  to  be  in  the  least  degree  sensible  ;  and  no  sign  of  pain 
is. given,  when  the  Sympathetic  trunks  themselves  are  irritated.  But 
in  certain  diseased  conditions  of  those  organs,  violent  pains  are  felt 
in  them;  and  these  pains  can  only  be  produced,  through  the  me- 
dium of  fibres  communicating  with  the  sensorium  through  the  spinal 
nerves. 

929.  It  is  difficult  to  speak  with  any  precision,  as  to  the  functions 
of  the  Sympathetic  system.  There  is  much  reason  to  believe,  how- 
ever, that  it  constitutes  the  channel,  through  which  the  passions  and 
emotions  of  the  mind  affect  the  Organic  functions;  and  this  especially 
through  its  power  of  regulating  the  calibre  of  the  arteries.  We  have 
examples  of  the  influence  of  these  states  upon  the  Circulation,  in  the 
palpitation  of  the  heart  which  is  produced  by  an  agitated  state  of 
feeling ;  in  the  Syncope,  or  suspension  of  the  heart's  action,  which 
sometimes  comes  on  from  a  sudden  shock  ;  in  the  acts  of  blushing 
and  turning  pale,  which  consist  in  the  dilatation  or  contraction  of  the 
small  arteries  ;  in  the  sudden  increase  of  the  salivary,  lachrymal,  and 
mammary  secretions,  under  the  influence  of  particular  states  of  mind, 
which  increase  is  probably  due  to  the  temporary  dilatation  of  the  ar- 
teries that  supply  the  glands,  as  in  the  act  of  blushing ;  and  in  many 


528  SENSATION. 

other  phenomena.  It  is  probable  that  the  Sympathetic  system  not 
only  thus  brings  the  Organic  functions  into  relation  with  the  Animal: 
but  that  it  also  tends  to  harmonize  the  former  with  each  other,  so  as 
to  bring  the  various  acts  of  secretion,  nutrition,  &c.,  into  mutual  con- 
formity. Of  the  distinctive  function  of  the  gray  or  organic  fibres,  we 
have  no  knowledge  whatever.  Possibly  they  may  have  some  direct 
influence  upon  the  chemical  processes,  which  are  involved  in  these 
changes,  and  may  thus  affect  the  quality  of  the  secretions  ;  whilst  the 
office  of  the  white  fibres  is  rather  to  regulate  the  diameter  of  the  blood- 
vessels supplying  the  glands,  and  thus  to  determine  the  quantity  of 
their  products. 


CHAPTER  XIII. 

OF  SENSATION,  GENERAL  AND  SPECIAL. 

1 .   Of  Sensation  in  general, 

930.  All  beings  of  a  truly  Animal  Nature  possess,  there  is  good 
reason  to  believe,  a  consciousness  of  their  own  existence,  first  derived 
from  a  feeling  of  some  of  the  corporeal  changes  taking  place  within 
themselves ;  and  also  a  greater  or  less  amount  of  sensibility  to  the 
condition  of  external  things.  This  consciousness  of  what  is  taking 
place  within  and  around  the  individual,  is  all  derived  from  impres- 
sions  made  upon  its  afferent  nervous  fibres ;  which,  being  conveyed 
by  them  to  the  central  sensorium^  are  \\\exefeU  (§  390).  Of  the  mode 
in  w^hich  the  impression,  hitherto  a  change  of  a  physical  character,  is 
there  made  to  act  upon  the  mind^  we  are  absolutely  ignorant ;  we  only 
know  the  fact.  Although  we  commonly  refer  our  various  sensations 
to  the  parts  at  which  the  impressions  are  made, — as,  for  instance, 
when  we  say  that  we  have  a  pain  in  the  hand,  or  an  ache  in  the  leg, 
— we  really  use  incorrect  language  ;  for  though  we  may  refer  our 
sensations  to  the  parts  where  the  impression  is  first  made  on  the 
nerves,  they  are  really  felt  in  the  brain.  This  is  evident  from  two 
facts  ; — first,  that  if  the  nervous  communication  between  the  part  and 
the  brain,  be  interrupted,  no  impressions,  however  violent,  can  make 
themselves  felt;  and  second,  that  if  the  trunk  of  the  nerve  be  irritated 
or  pinched,  anywhere  in  its  course,  the  pain  which  is  felt  is  referred, 
not  to  the  point  injured,  but  to  the  surface  to  which  these  nerves 
are  distributed.  Hence  the  well-known  fact  that,  for  some  time 
after  the  amputation  of  a  limb,  the  patient  feels  pains,  which  he 
refers  to  the  fingers  or  toes  that  have  been  removed  ;  this  continues, 
until  the  irritation  of  the  cut  extremities  of  the  nervous  trunks  has 
subsided. 


SENSATION;— GENERAL  AND  SPECIAL.  529 

931.  It  would  seem  probable  that,  among  the  lower  tribes  of  Ani- 
raals,  there  exists  no  other  kind  of  sensibility,  than  that  termed  gene- 
ral or  common;  which  exists,  in  a  greater  or  less  degree,  in  every 
part  of  the  bodies  of  the  higher.  It  is  by  this,  that  we  feel  those 
impressions,  made  upon  our  bodies  by  the  objects  around  us,  which 
produce  the  various  modifications  of  pain^  the  sense  of  contact  or 
resistance,  the  sense  of  variations  of  temperature,  and  others  of  a 
similar  character.  From  what  w^as  formerly  stated  (§  403)  of  the 
dependence  of  the  impressibility  of  the  sensory  nerves,  upon  the 
activity  of  the  circulation  in  the  neighbourhood  of  their  extremities, 
it  is  obvious  that  no  parts  destitute  of  blood-vessels  can  receive 
such  impressions,  or  (in  common  language)  can  possess  sensibility. 
Accordingly  we  find  that  the  hair,  nails,  teeth,  cartilages,  and  other 
parts  that  are  altogether  extra-vascular,  are  themselves  destitute  of 
sensibility ;  although  certain  parts  connected  with  them,  such  as  the 
bulb  of  the  hair,  or  the  vascular  membrane  lining  the  pulp-cavity  of 
the  tooth,  may  be  acutely  sensitive.  Again,  in  tendons,  ligaments, 
fibro-cartilages,  bones,  &c.,  whose  substance  contains  very  few  ves- 
sels, there  is  but  a  very  low  amount  of  sensibility.  On  the  other 
hand,  the  skin  and  other  parts,  which  are  peculiarly  adapted  to  re- 
ceive such  impressions,  are  extremely  vascular:  and  it  is  interesting 
to  observe,  that  some  of  the  tissues  just  mentioned  become  acutely 
sensible,  when  new  vessels  form  in  them  in  consequence  of  diseased 
action.  It  does  not  necessarily  follow,  however,  that  parts  should  be 
sensible  in  a  degree  proportional  'to  the  amount  of  blood  they  may 
contain ;  for  this  blood  may  be  sent  to  them  for  other  purposes,  and 
they  may  contain  but  a  small  number  of  sensory  nerves.  Thus,  it  is 
a  condition  necessary  to  the  action  of  Muscles,  that  they  should  be 
copiously  supplied  with  blood  (§359);  but  they  are  by  no  means 
acutely  sensible  ;  and,  in  like  manner.  Glands,  which  receive  a  large 
amount  of  blood  for  their  peculiar  purposes,  are  far  from  possessing  a 
high  degree  of  sensibility. 

932.  But  besides  the  general,  or  common  sensibility,  which  is  dif- 
fused over  the  greater  part  of  the  body,  in  most  animals,  there  are 
certain  parts,  which  are  endowed  with  the  property  of  receiving  im- 
pressions of  a  peculiar  or  special  kind,  such  as  sounds  or  odours,  that 
would  have  no  influence  on  the  rest ;  and  the  sensations  which  these 
excite,  being  of  a  kind  very  different  from  those  already  mentioned, 
arouse  ideas  in  our  minds,  which  we  should  never  have  gained  with- 
out them.  Thus,  although  we  can  acquire  a  knowledge  of  the  shape 
and  position  of  objects  by  the  touch,  we  could  form  no  notion  of  their 
colour  without  sight,  of  their  sounds  without  hearing,  or  of  their 
odours  without  smell.  The  nerves  which  convey  these  special  im- 
pressions, as  already  mentioned,  are  not  able  to  receive  those  of  a 
common  kind  ;  thus  the  eye,  however  well  fitted  for  seeing,  would  not 
feel  the  touch  of  the  finger,  if  it  were  not  supplied  by  branches  from 
the  5th  pair,  as  well  as  by  the  Optic.  Nor  can  the  different  nerves  of 
special  sensation  be  aflfected  by  impressions,  that  are  adapted  to  ope- 


530  OF  SENSATION  IN  GENERAL. 

rate  on  others  ;  thus  the  ear  cannot  distinguish  the  slightest  difference 
between  a  luminous  and  a  dark  object ;  nor  could  the  eye  distinguish 
a  sounding  body  from  a  silent  one,  except  when  the  vibrations  can  be 
seen.  But  Electricity  possesses  the  remarkable  power,  when  trans- 
mitted along  the  several  nerves  of  special  sense,  of  exciting  the  sen- 
sations peculiar  to  each  ;  and  thus,  by  proper  management,  this  single 
agent  may  be  made  to  produce  flashes  of  light,  distinct  sounds,  a 
phosphoric  odour,  a  peculiar  taste,  and  a  pricking  feeling,  in  the  same 
individual,  at  one  time.  Each  kind  of  sensation  may  also  be  excited, 
however,  by  mechanical  irritation  of  the  nerve  which  is  subservient  to 
it. — The  feeling  of  pain  may  be  induced  by  impressions  made  upon 
the  nerves  of  special  sense,  as  well  as  upon  those  of  feeling ;  if  these 
impressions  be  too  violent  or  excessive.  Thus  the  dazzling  of  the 
eye  by  a  strong  light,  and  still  more,  the  action  of  a  moderate  light  in 
an  irritable  state  of  the  retina, — sudden  loud  sounds,  or  even  sounds 
of  moderate  intensity  but  of  peculiar  harshness,— powerful  odours, 
even  such  as  are  agreeable  in  moderation, — produce  feelings  of  un- 
easiness, which  may  be  properly  called  painful,  even  though  they  are 
different  from  those  excited  through  the  nerves  of  common  sensation. 

933.  As  a  general  rule,  it  may  be  stated,  that  the  violent  excite- 
ment oi any  sensation  is  disagreeable;  even  when  the  same  sensation, 
experienced  in  a  moderate  degree,  may  be  a  source  of  extreme  plea- 
sure. But  the  question  of  degree  is  relative^  rather  than  absolute ; 
that  is,  a  sensation  may  be  felt  as  extremely  violent  by  one  individual ; 
whilst  another,  who  is  more  accustomed  to  sensations  of  the  same 
kind,  is  not  disagreeably  affected  by  it.  Thus,  our  sensations  of  heat 
and  cold  are  entirely  governed  by  the  previous  condition  of  the  parts 
affected;  as  is  shown  by  the  well-known  experiment,  of  putting. one 
hand  in  hot  water,  the  other  in  cold,  and  then  transferring  them  both 
to  tepid  water, — which  will  seem  coo]  to  the  one  hand,  and  warm  to 
the  other.  The  same  is  the  case  in  regard  to  light  and  sound,  smell 
and  taste.  A  person  going  out  of  a  totally  dark  room,  into  one  mode- 
rately bright,  is  for  the  time  painfully  impressed  by  the  light,  but  soon 
becomes  habituated  to  it;  whilst  another  who  enters  it  from  a  room 
brilliantly  illuminated,  will  consider  it  dark  and  gloomy. 

934.  The  intensity  with  w^hich  sensations  are  felt,  therefore,  de- 
pends upon  the  degree  of  change  which  they  produce  in  the  sensorium. 
The  more  frequent  the  recurrence  of  any  particular  sensation,  the  more 
does  the  system  become  adapted  to  it,  and  the  less  change  does  it 
produce.  It  is,  therefore,  perceived  in  a  less  and  less  degree,  and  at 
last  it  ceases  to  excite  attention.  The  stoppage  of  a  constantly-recur- 
ring sensation,  however,  will  produce  a  change,  which  makes  as 
strong  an  impression  on  the  system  as  its  first  commencement ;  thus 
there  are  persons,  who  have  become  so  habituated  to  the  sound  of  a 
waterfall  or  even  of  a  forge-hammer,  that  they  cannot  sleep  anywhere 
but  in  its  vicinity  ;  and  it  is  well  known  that,  when  a  person  has  gone 
to  sleep  under  the  influence  of  some  continuous  or  frequently-recur- 
ring sound  (such  as  the  voice  of  a  reader,  the  dropping  of  water,  the 


r 


EFFECTS  OF  ATTENTION.  531 

tread  of  a  sentinel,  &c.),  the  cessation  of  the  sound  will  cause  his 
awaking. 

935.  The  acuteness  of  particular  sensations  is  influenced  in  a  re- 
markable degree,  by  the  attention  they  receive  from  the  mind.  If  the 
mind  be  entirely  inactive,  as  in  profound  sleep,  no  sensation  what- 
ever is  produced  by  very  feeble  impressions ;  on  the  other  hand,  when 
the  mind  is  from  any  cause  strongly  directed  upon  them,  impressions 
very  feeble  in  themselves  produce  sensations  of  even  painful  acute- 
ness. It  is  in  this  manner,  that  the  habit  of  attending  to  sensations 
of  any  particular  class,  increases  their  vividness  ;  so  that  they  are  at 
once  perceived  by  an  individual  on  the  watch  for  them,  when  they 
do  not  excite  the  observation  of  others.  We  may  even,  by  a  strong 
effort,  direct  the  mind  into  one  particular  channel,  so  as  to  receive 
only  those  sensations  which  have  reference  to  it,  and  to  be  uncon- 
scious quoad  all  others.  Thus,  the  application  of  the  mind  to  some 
particular  train  of  thought  may  prevent  our  being  conscious  of  any- 
thing that  is  going  around  or  within  us, — the  conversation  of  friends, 
— the  striking  of  the  clock, — the  calls  of  hunger,  &c.  This  abstrac- 
tion may  be  altogether  voluntary ;  and  the  possession  of  the  power  of 
thus  withdrawing  the  mind  at  will  from  the  influence  of  external  dis- 
turbing causes,  and  of  fixing  it  upon  any  particular  train  of  ideas,  is 
an  extremely  valuable  one.  But  it  may  also  be  involuntary,  and  may 
be  a  source  of  inconvenience  from  its  tendency  to  recur  at  improper 
times, — producing  the  habitual  state  which  is  known  as  absence  of 
mind  or  revery. 

936.  It  is  desirable  that  we  should  make  a  distinction,  between 
the  sensations  themselves,  and  the  ideas  which  are  the  immediate 
results  of  those  sensations,  when  they  are  perceived  by  the  mind. 
These  ideas  relate  to  the  cause  of  the  sensation,  or  the  object  by  which 
the  impression  is  made.  Thus,  the  formation  of  the  picture  of  an 
object,  upon  the  retina,  produces  a  certain  impression  upon  the  optic 
nerve ;  which  being  conveyed  to  the  sensorium,  excites  a  correspond- 
ing sensation,  with  which,  in  all  ordinary  cases,  we  immediately  con- 
nect an  idea  of  the  nature  of  the  object.  So  closely,  indeed,  is  this 
idea  usually  related  to  the  sensation,  that  we  are  not  in  the  habit  of 
making  a  distinction  between  them.  Thus  I  may  say  at  this  moment, 
**  I  see  a  book  on  the  table  before  me ;"  the  fact  being,  that  I  am  con- 
scious of  a  certain  picture,  which  conveys  to  my  mind  the  ideas  of  a 
book  and  of  a  table,  and  of  their  relative  positions  ;  these  ideas  being 
(in  Man)  the  result  of  experience  and  association, — in  fact,  originating 
in  the  immediate  application  of  the  knowledge  we  have  previously 
acquired,  that  a  certain  object,  whose  picture  we  see,  is  a  book,  an- 
other object  a  table,  and  so  on.  We  are  liable  to  be  deceived  in  this 
assumption  ;  as  when,  by  a  clever  imitation,  a  picture  on  a  plane 
surface  is  made  to  represent  an  object  in  relief,  so  perfectly  as  at 
once  to  excite  the  idea  of  the  latter, — which  may  not  be  corrected, 
until  we  have  ascertained  by  the  touch  the  flatness  of  the  real  object. 

937.  This  production  of  ideas,  by  the  agency  of  sensations,  is  a 


532  PERCEPTIONS,  INTUITIVE  AND  ACQUIRED. 

process  altogether  mental,  and  dependent  upon  the  laws  of  Mind. 
We  find  that  some  of  these  perceptions  or  elementary  notions  are  intui- 
tive; that  is,  they  are  prior  to  all  experience,  and  are  necessarily  con- 
nected with  the  sensation  which  produces  them,  as  reflex  movements 
are  with  the  impression  that  excites  them.  This  seems  to  be  the 
case,  for  example,  with  regard  to  erect  vision.  There  is  no  reason 
whatever  to  think,  that  either  infants  or  any  of  the  lower  animals  see 
objects  in  an  inverted  position,  until  they  have  corrected  their  notion 
by  the  touch ;  for  there  is  no  reason  why  the  inverted  picture  on  the 
retina  should  give  rise  to  the  idea  of  the  inversion  of  the  object.  The 
picture  is  so  received  by  the  mind,  as  to  convey  to  us  an  idea  of  the 
position  of  external  objects,  which  harmonizes  with  the  ideas  we 
derive  through  the  touch ;  and  whilst  we  are  in  such  complete  igno- 
rance of  the  manner  in  which  the  mind  becomes  conscious  of  the 
sensation  at  all,  we  need  not  feel  any  difficulty  about  the  mode  in 
which  this  conformity  is  effected.  But  in  Man,  as  already  stated,  the 
attaching  definite  ideas  to  certain  groups  of  lines,  colours,  &c.,  with 
respect  to  the  objects  they  represent,  is  a  subsequent  process,  in 
which  experience  and  memory  are  essentially  concerned ;  as  we  see 
particularly  well,  in  cases  presently  to  be  referred  to,  in  which  the 
sense  of  sight  has  been  acquired  comparatively  late  in  life,  and  in 
which. the  mode  of  using  it,  and  of  connecting  the  sensations  received 
through  it  with  those  received  through  the  touch,  has  had  to  be 
learned  by  a  long-continued  training.  The  elementary  notions  thus 
formed, — which  may,  by  long  habit,  present  themselves  as  immedi- 
ately and  unquestionably,  as  if  they  were  intuitive, — are  termed  ac- 
quired perceptions. 

938.  It  is  probable  that,  among  the  lower  animals,  the  proportion 
of  intuitive  perceptions  is  much  greater  than  in  Man ;  whilst,  on  the 
other  hand,  his  power  of  acquiring  perceptions  is  much  greater  than 
theirs.  So  that,  whilst  the  young  of  the  lower  animals  very  soon 
becomes  possessed  of  all  the  knowledge,  which  is  necessary  for  the 
acquirement  of  its  food,  the  construction  of  its  habitation,  &c.,  its 
range  is  very  limited,  and  it  is  incapable  of  attaching  any  ideas  to  a 
great  variety  of  objects,  of  which  the  Human  mind  takes  cognizance. 
This  correspondence  between  the  acquired  perceptions  of  Man,  and 
the  intuitive  perceptions  of  many  of  the  lower  animals,  is  strikingly 
evident  in  regard  to  the  power  of  measuring  distance.  This  is 
acquired  very  gradually  by  the  Human  infant,  or  by  a  person  who  has 
first  obtained  the  faculty  of  sight  later  in  life ;  but  it  is  obviously  pos- 
sessed by  many  of  the  lower  animals,  to  whose  maintenance  it  is  essen- 
tial immediately  upon  their  entrance  into  the  world.  Thus  a  Fly- 
catcher, immediately  after  its  exit  from  the  egg,  has  been  known  to 
peck  at  and  capture  an  insect, — an  action  which  requires  a  very  exact 
appreciation  of  distance,  as  well  as  a  power  of  precisely  regulating 
the  muscular  movements  in  accordance  with  it. 


I 


SENSE  OF  TOUCH.— CUTANEOUS  PAPILLJE.  533 


2.   Of  the  Sense  of  Touch. 

939.  By  the  sense  of  Touch  is  usually  understood  that  modification 
of  the  common  sensibility  of  the  body  of  which  the  surface  of  the  Skin 
is  the  especial  seat,  but  which  exists  also  in  some  of  its  internal  re- 
flexions. In  some  animals,  as  in  Man,  nearly  the  whole  exterior  of  the 
body  is  endowed  with  it,  in  no  inconsiderable  degree  ;  whilst  in  others, 
as  the  greaternumber  of  Mammalia,  most  Birds,  Reptiles,  and  Fishes, 
and  a  large  proportion  of  the  Invertebrata,  the  greater  part  of  the  body 
is  so  covered  with  hairs,  scales,  bony  or  horny  plates,  shells  of  various 
kinds,  complete  horny  envelops,  &c.,  as  to  be  nearly  insensible;  and 
the  faculty  is  restricted  to  particular  portions  of  the  surface,  or  to  or- 
gans projecting  from  it,  which  often  possess  a  peculiarly  high  degree 
of  this  endowment.  Even  in  Man,  the  acuteness  of  the  sensibility  of 
the  cutaneous  surface  varies  greatly  in  different  parts ;  being  greatest 
at  the  extremities  of  the  fingers,  and  in  the  lips;  and  least  in  the  skin 
of  the  trunk,  arm,  and  thigh.  Thus  the  two  points  of  a  pair  of  com- 
passes (rendered  blunt  by  bits  of  cork)  can  be  separately  distinguished 
by  the  point  of  the  middle  finger,  when  approximated  so  closely  as  one- 
third  of  a  line ;  whilst  they  require  to  be  opened  so  widely  as  30  lines 
from  each  other,  to  be  separately  distinguished,  when  pressed  upon 
the  skin  over  the  spine,  or  upon  that  of  the  middle  of  the  arm  or 
thigh. 

940.  The  impressions  that  produce  the  sense  of  Touch  are  received 
through  the  sensory  papillcB^  with  which 

the  surface  of  the  true  Skin  is  beset, —  Fig.  i46. 

more  or  less  closely  according  to  the  part 
of  it  that  is  examined.  These  papillse  are 
minute  elevations,  which  enclose  loops  of 
capillary  vessels  (Fig.  146),  and  branches 
of  the  sensory  nerves.  With  regard  to  the 
precise  course  of  the  latter,  there  is  some 
uncertainty;  but  it  is  probable  from  ana- 
logy,   that   the    representation    given    of 


lltel^:* 


wmmmm 


them     by    Gerber     (Fig.     147),    is    in     the        Capillary  network  at  margin  of  lips. 

main  correct;  and  that  each  loop  of  the  Sen- 
sory nerve  is  surrounded  by  a  small  quantity  of  vesicular  matter,  on 
some  change  in  which  the  formation  of  the  sensory  impression  is 
immediately  dependent.  It  is  peculiar  to  the  sense  of  Touch,  and 
to  that  of  taste  (which  is  a  modification  of  it)  that  the  impression 
must  be  made  by  the  contact  of  the  object  itself  with  the  sensory 
surface  and  not  through  any  intermediate  agency.  The  only  excep- 
tion to  this  is  in  regard  to  the  sense  of  Temperature,  which  seems  to 
be  in  many  respects  different  from  ordinary  touch  ;  here  the  proximity 
of  the  warm  or  cold  body  is  sufficient, — the  impressions  being  made 
after  the  manner  of  those  of  odours,  sounds,  &c.  It  is  worth  re- 
marking, with  reference  to  the  question  of  the  special  nature  of  the 


534  CUTANEOUS  PAPILLJE.— SENSE  OF  RESISTANCE. 

sensory  fibres,  which  are  the  channel  of  these  impressions,  that  no 
mechanical  irritation  of  the  nerves  of  common  sensation  ever  seems 

Fig.  147. 


Distribution  of  the  tactile  nerves  at  the  extremity  of  the  human  thumb,  as  seen  in  a  thin  perpendicu- 
lar section  of  the  skin. 

to  excite  sensations  of  heat  or  cold ;  these  being  apparently  as  distinct 
from  the  sense  of  contact,  as  they  are  from  that  of  light  or  sound. 

941.  The  only  idea  communicated  to  our  minds,  when  this  sense  is 
exercised  in  its  simplest  form,  is  that  of  resistance;  and  we  cannot  acquire 
a  notion  of  the  size  or  shape  of  an  object,  or  of  the  nature  of  its  sur- 
face, through  this  sense  alone,  unless  we  move  the  object  over  our  own 
sensory  organ  or  pass  the  latter  over  the  former.  By  the  various  de- 
grees of  resistance  which  we  then  encounter,  we  form  our  estimate  of 
the  hardness  or  softness  of  the  body.  By  the  impressions  made  upon 
our  sensory  papillae,  when  they  are  passed  over  its  surface,  we  form 
our  idea  of  its  smoothness  or  roughness.  But  it  is  through  the  mus- 
cular sense  which  renders  us  cognizant  of  the  relative  position  of  the 
fingers,  the  amount  of  movement  the  hand  has  performed  in  passing 
over  the  object,  and  of  other 'impressions  of  like  nature,  that  we  ac- 
quire our  notions  of  the  size  and  figure  of  the  object;  and  hence  we 
perceive,  that  the  sense  of  touch,  without  the  power  of  giving  motion 
to  the  tactile  organ,  would  have  been  of  comparatively  little  use.  It 
is  chiefly  in  the  variety  of  movements,  of  which  the  hand  of  Man  is 
capable, — thus  conducive  as  they  are,  not  merely  to  his  prehensile 
powers,  but  to  the  exercise  of  his  sensory  endowments, — that  it  is 
superior  to  that  of  every  other  animal;  and  it  cannot  be  doubted,  that 
this  affords  us  a  very  important  means  of  acquiring  information  in  re- 
gard to  the  external  world,  and  especially  of  correcting  many  vague 
and  fallacious  notions,  which  we  should  derive  from  the  sense  of  Sight, 
if  used  alone.  On  the  other  hand,  it  must  be  evident  that  our  know- 
ledge would  have  but  a  very  limited  range,  if  this  sense  were  the  only 
medium,  through  which  we  could  acquire  ideas.  Of  this  we  have  the 
clearest  evidence  in  the  very  imperfect  development  of  the  mental 
powers,  in  those  unfortunate  persons  who  have  suflfered  under  the 
deprivation  of  sight  and  hearing  from  their  birth,  and  who  have  been 
consequently  cut  off*  from  the  most  direct  means  of  profiting  by  the 
knowledge  possessed  by  their  fellow-beings,  through  want  of  power 
to  use  the  organs  of  speech.     It  is  only  where  such  individuals  have 


SENSE  OF  TEMPERATURE.— NERVES  OF  TASTE.  535 

fallen  under  the  care  of  judicious  and  persevering  instructors,  that 
their  mental  powers  have  been  called  into  their  due  activity,  or  that 
any  ideas  have  been  awakened,  beyond  those  immediately  connected 
with  the  gratification  of  the  animal  wants,  or  with  painful  or  pleasur- 
able sensations.  Thus  a  mind,  quite  capable  of  being  aroused  to  activ- 
ity and  enjoyment,  may  remain  in  a  condition  nearly  allied  to  that  of 
idiocy,  simply  for  want  of  the  sensations  requisite  to  produce  ideas  of 
a  higher  and  more  abstract  character  than  those  derived  through  the 
senses  of  Touch,  Taste,  and  Smell. 

942.  It  is  not  by  any  means  certain,  whether  the  sense  of  Tempe- 
rature is  not  conveyed  by  a  set  of  fibres,  altogether  distinct  from  those 
which  minister  to  the  proper  sense  of  Touch  or  resistance.  For  many 
cases  are  on  record,  in  which  it  has  been  lost,  whilst  the  ordinary 
sense  of  touch  remains ;  and  it  is  sometimes  preserved,  when  there  is  a 
complete  loss  of  every  other  kind  of  sensibility.  So  again  we  find 
that  the  subjective  sensations  of  temperature,— ^-that  is,  sensations  which 
originate  from  changes  in  the  body  itself,  not  from  external  impres- 
sions,— are  frequently  excited  quite  independently  of  the  tactual  sen- 
sations ;  a  person  being  sensible  of  heat  or  of  chilliness  in  some  part  of 
his  body,  without  any  real  alteration  of  its  temperature,  and  without 
any  corresponding  affection  of  the  tactual  sensations. — It  is  curious 
that  the  intensity  of  the  sensation  of  temperature  should  depend,  not 
merely  upon  the  relative  degree  of  heat  to  which  the  part  is  exposed 
(§  933),  but  also  upon  the  extent  of  the  surface  over  which  it  is  applied; 
— a  weaker  impression  made  on  a  larger  surface,  seeming  more  power- 
ful than  a  stronger  impression  made  on  a  small  surface.  Thus,  if  the 
forefinger  of  one  hand  be  immersed  in  water  at  104°,  and  the  whole 
of  the  other  hand  be  plunged  in  water  at  102°,  the  cooler  water  will 
be  thought  the  warmer;  whence  the  well-known  fact,  that  water  in 
which  a  finger  can  be  held  without  discomfort,  will  produce  a  scald- 
ing sensation  when  the  entire  hand  is  immersed  in  it. 

3.   Of  the  Sense  of  Taste. 

943.  The  sense  of  Taste,  like  that  of  Touch,  is  excited  by  the  direct 
contact  of  particular  substances  with  certain  parts  of  the  body:  but  it 
is  of  a  much  more  refined  nature  than  touch ;  inasmuch  as  it  commu- 
nicates to  us  a  knowledge  of  properties,  which  that  sense  would  not 
reveal  to  us.  All  substances,  however,  do  not  make  an  impression  on 
the  organ  of  Taste.  Some  have  a  strong  savour,  others  a  slight  one, 
and  others  are  altogether  insipid.  The  cause  of  these  differences  is 
not  altogether  understood  ;  but  it  may  be  remarked  that,  in  general, 
bodies  which  cannot  be  dissolved  in  water,  alcohol,  &c.,  and  which 
thus  cannot  be  presented  to  the  gustative  papillse  in  a  state  of  solution, 
have  no  taste.  This  sense  has  for  its  chief  purpose,  to  direct  animals 
in  their  choice  of  food  ;  hence  its  organ  is  always  placed  at  the  en- 
trance to  the  digestive  canal.  In  higher  animals,  the  tongue  is  the 
principal  seat  of  it ;  but  other  parts  of  the  mouth  are  also  capable  of 


536      NERVES  OF  TASTE.— COMPOUND  NATURE  OF  THE  SENSE. 

receiving  the  impression  of  certain  savours.     The  mucous  membrane 

which  covers  the  tongue  is  copiously  supplied  with  papillae,  of  various 

forms  and  sizes.     Those  of  simplest  structure  closely  resemble  the 

cutaneous  papillae ;  but  there  are  others, 
F'gi^a  which  resemble  clusters  of  such  papillae, 

each  being  composed  of  a  fasciculus  of 
looped  capillaries  (Fig.  148),  and  probably 
containing  a  similar  fasciculus  of  nervous 
loops,  lying  in  the  midst  of  vesicular  mat- 
ter. No  difference  of  function  has  yet 
been  ascertained  to  exist  among  the  several 
forms  of  lingual  papillae.  When  the  pa- 
pillae are  called  into  action  by  the  contact 

papilla  oFthrrgJa."' '""'''°""    of  substances  having  a  strong  savour,  they 

not  unfrequently  become  very  turgid,  by  a 

distension  of  their  vessels  analogous  to  that  which  occurs  in  erection; 

and  they  rise  up  from  the  surface  of  the  mucous  membrane,  so  as  to 

produce  a  decided  roughness  of  its  surface. 

944.  There  has  been  much  discrepancy  of  opinion  as  to  the  nerve 
which  is  specially  concerned  in  the  sense  of  Taste.  The  tongue  is 
supplied  by  two  sensory  nerves;  the  lingual  branch  of  the  5th  pair; 
and  the  glosso-pharyngeal.  The  former  chiefly  supplies  the  upper 
surface  of  the  front  of  the  tongue,  and  is  copiously  distributed  to  the 
papillae  near  the  tip.  The  latter  is  mostly  distributed  upon  the  mu- 
cous surface  of  the  fauces,  and  upon  the  back  of  the  tongue ;  but  it 
sends  a  branch  forwards,  beneath  the  lateral  margin  on  each  side, 
which  supplies  the  edges  and  inferior  surface  of  the  tip  of  the  tongue, 
and  inosculates  with  the  preceding.  There  is  reason  to  believe,  from 
experiment,  that  the  gustative  sensibility  of  the  tongue  is  not  destroyed 
by  section  of  either  of  these  nerves ;  though  it  is  impaired  by  the 
total  or  partial  loss  of  sensibility  over  certain  parts  of  the  surface. 
There  seems  good  reason  to  conclude,  that  the  lingual  branch  of  the 
5th  pair  is  the  nerve  through  which  the  sense  of  Taste,  as  well  as 
that  of  Touch,  is  exercised,  in  the  parts  of  the  tongue  to  which  it  is 
specially  distributed, — which  are  those  that  possess  both  senses  in  the 
most  acute  degree  ;  and  that  the  Glosso-pharyngeal  is  subservient  to 
the  same  functions  in  the  parts  supplied  by  it,  being  probably  the 
exclusive  channel,  also,  through  which  the  impressions  made  by 
disagreeable  substances  taken  into  the  mouth  are  propagated  to  the 
Medulla  Oblongata,  so  as  to  produce  nausea  and  excite  efforts  to 
vomit.  The  latter  nerve  is  also,  as  we  have  seen,  the  principal  chan- 
nel of  the  impressions,  that  give  rise  to  the  reflex  act  of  swallowing; 
with  which  the  5th  pair  is  concerned  in  a  much  inferior  degree 
(§  897). 

945.  A  considerable  part  of  the  impression  produced  by  many  sub- 
stances taken  into  the  mouth,  is  received  through  the  sense  of  Smell, 
rather  than  through  that  of  Taste.  Of  this,  any  one  may  easily  satisfy 
himself,  by  closing  the  nostrils,  and  breathing  through  the  mouth  only, 


CONDITIONS  OF  THE  SENSE  OF  SMELL. 


537 


whilst  holding  in  his  mouth,  or  even  rubbing  between  his  tongue  and 
his  palate,  some  aromatic  substance  ;  its  taste  is  then  scarcely  recog- 
nized, although  it  is  immediately  perceived  when  the  nasal  passages 
are  reopened,  and  its  effluvia  are  drawn  into  them.  There  are  many 
substances,  however,  which  have  no  aromatic  or  volatile  character; 
and  whose  taste,  though  not  in  the  least  dependent  upon  the  action  of 
the  nose,  is  nevertheless  of  a  powerful  character ;  but  these  for  the 
most  part  produce,  by  irritating  the  mucous  membrane,  a  sense  of 
pungency^  allied  to  that  which  the  same  substances  (acids,  for  instance, 
pepper,  or  mustard),  will  produce,  when  applied  to  the  skin  for  a  suffi- 
cient length  of  time,  especially  if  the  Epidermis  have  been  removed. 
Such  sensations,  therefore,  are  evidently  of  the  same  kind  with  those 
of  Touch  ;  differing  from  them  only  in  the  degree  of  sensibility  of  the 
organ,  through  which  they  are  received.  The  sense  of  Taste,  then, 
in  its  ordinary  acceptation,  may  be  regarded  as  a  compound  of  those 
of  Smell  and  Touch. 


4.   Of  the  Sense  of  Smell. 

946.  Certain  bodies  possess  the  property  of  exciting  sensations  of 
a  peculiar  nature,  which  cannot  be  perceived  by  the  organs  of  taste 
or  touch,  but  which  seem  to  depend  upon  the  diffusion  of  the  particles 
of  the  substance  through  the  surrounding  air,  in  a  state  of  extreme 
Ininuteness.  As  the  so- 
lubility of  a  substance  Tig.u9. 
in  liquid  seems  a  neces- 
sary condition  of  its  ex- 
citing the  sense  of  Taste, 
so  does  its  volatility,  or 
tendency  to  a  vaporous 
state,  appear  requisite 
for  its  having  Odorous 
properties.  Most  vola- 
tile substances  are  more 
or  less  odorous ;  whilst 
those  which  do  not 
readily  transform  them- 
selves into  vapour,  usu- 
ally possess  little  or  no 
fragrance  in  the  liquid 
or  solid  state,  but  ac- 
quire strong  odorous 
properties,  as  soon  as 
they  are  converted  into 
vapour, — by  the  aid  of 

heat,  for  example.  There  are  some  solid  substances,  which  possess 
very  strong  odorous  properties,  without  losing  weight  in  any  appre- 
ciable degree  by  the  diffusion  of  their  particles  through  the  air.     This 


A  view  of  the  First  pair,  or  Olfactory  Nerves,  with  the  Nasal 
Branches  of  the  Fifth  pair;  1,  frontal  sinus;  2,  sphenoidal  sinus ; 
3,  hard  palate;  4,  bulb  of  olfactory  nerve;  5,  branches  of  the 
olfactory  nerve  on  the  superior  and  middle  turbinated  bones ; 
6,  spheno-palatine  nerves  from  the  second  branch  of  the  fifth 
pair;  7,  internal  nasal  nerve  from  the  first  branch  of  the  fifth; 
8,  branches  of  7  to  the  Schneiderian  membrane ;  9,  ganglion  of 
Cloquet  in  the  foramen  incisivum;  10,  anastomosis  of  the 
branches  of  the  fifth  pair  on  the  inferior  turbinated  bone. 


538  CONDITIONS  OF  THE  SENSE  OF  SMELL. 

is  the  case,  for  example,  with  Musk  ;^a  grain  of  which  has  been  kept 
freely  exposed  to  the  air  of  a  room,  whose  door  and  windows  were 
constantly  open,  for  a  period  often  years ;  during  which  time  the  air, 
thus  continually  changed,  was  completely  impregnated  with  the  odour 
of  musk;  and  yet,  at  the  end  of  that  time,  the  particle  was  not  found 
to  have  perceptibly  diminished  in  weight.  We  can  only  attribute 
this  result  to  the  extreme  minuteness  of  the  division  of  the  odorous 
particles  of  this  substance.  There  are  other  odorous  solids,  such  as 
Camphor,  which  rapidly  lose  weight  by  the  loss  of  particles  from  their 
surface,  when  freely  exposed  to  the  air. 

947.  The  conditions  of  the  sense  of  Smell  are  very  simple.  The 
Olfactory  nerve  is  minutely  distributed  over  the  Schneiderian  mem- 
brane, which  is  itself  highly  vascular.  The  arrangement  of  the  ulti- 
mate fibres  of  this  nerve  has  not  been  ascertained.  The  Schneiderian 
membrane  is  kept  constantly  but  moderately  moist,  by  a  mucous  se- 
cretion from  its  surface  ;  and  this  condition  is  essential  to  the  acute 
perception  of  odours.  If  the  mucous  surface  be  too  dry,  as  happens 
when  the  5th  pair  is  paralyzed,  the  sensation  is  blunted  or  even  de- 
stroyed; and  the  same  effect  is  produced  by  the  presence  of  too  copious 
a  secretion, — as  when  we  are  suffering  under  an  ordinary  cold. — The 
highest  part  of  the  nasal  fossae  appears  to  be  that  in  which  there  is 
the  most  acute  sensibility  to  odours;  and  hence  it  is  that,  when  we 
snuff  ihe.  air,  so  as  to  direct  it  into  this  portion  of  the  cavity,  we  per- 
ceive delicate  odours,  which  would  otherwise  have  escaped  us.  The 
acuteness  of  the  sense  of  Smell  depends,  in  no  small  degree,  upon 
the  extent  of  surface  exposed  by  the  membrane  lining  the  nasal  cavi- 
ty ;  and  in  this  respect,  Man  is  far  surpassed  by  many  of  the  lower 
Mammalia,  especially  the  Ruminants,  which  are  warned  by  its  means 
of  the  proximity  of  their  enemies.  The  habit  of  attention  to  sensory 
impressions  of  this  class,  however,  very  much  heightens  their  acute- 
ness ;  hence  in  those  who  suffer  under  blindness  and  deafness  con- 
jointly, it  is  usually  the  principal  means  by  which  individuals  are 
distinguished,  and  the  presence  of  strangers  recognized  ;  and  there 
are  cases,  in  which  individuals  in  a  state  of  Somnambulism  have  ex- 
hibited a  degree  of  acuteness  of  smell,  quite  comparable  to  that  which 
is  characteristic  of  Deer,  Antelopes,  &c. 

948.  Besides  ministering  to  the  sense  of  Smell,  by  stimulating  the 
secreting  powers  of  its  surface,  the  5th  pair  has  another  very  import- 
ant function, — that  of  endowing  the  interior  of  the  nose  with  com- 
mon sensibility,  and  thus  receiving  the  impression  produced  by  acrid 
or  pungent  substances,  which  act  upon  it  in  the  same  way  as  they 
do  upon  the  tongue.  Such  substances  are  felt,  by  the  irritation  they 
produce,  rather  than  smelt;  and  the  sensation  they  occasion  gives  rise 
to  the  consensual  act  o^ sneezing,  by  which  a  violent  blast  of  air  is  di- 
rected through  the  nasal  passages,  in  such  a  manner  as  to  clear  them 
of  the  irritating  matter,  whether  solid  (as  snuff),  fluid,  or  gaseous. 
Hence  this  action  may  be  excited  by  the  contact  of  an  irritant  with 
the  Schneiderian  membrane,  after  the  olfactory  nerve  has  been  di- 


SENSE  OF  HEARING.— ACOUSTIC  PRINCIPLES.  539 

vided,  if  the  branches  of  the  5th  pair  be  entire  ;  whilst  it  does  not 
take  place  when  the  5th  pair  is  paralyzed,  even  though  the  sense  of 
smell  is  retained. 

5.   Of  the  Sense  of  Hearing, 

949.  By  this  sense  we  become  acquainted  with  the  sounds  pro- 
duced by  bodies  in  a  certain  state  of  vibration ;  the  vibrations  being 
propagated  through  the  surrounding  medium,  by  the  corresponding 
waves  or  undulations  which  they  produce  in  it.  Although  air  is  the 
usual  medium  through  which  sound  is  propagated,  yet  liquids  or 
solids  may  answer  the  same  purpose.  On  the  other  hand,  no  sound 
can  be  propagated  through  a  perfect  vacuum. — It  is  a  fact  of  much 
importance,  in  regard  to  the  action  of  the  Organ  of  Hearing,  that  so- 
norous vibrations  which  have  been  excited,  and  are  being  transmitted, 
in  a  medium  of  one  kind,  are  not  imparted  with  the  same  readiness 
to  others.  The  following  conclusions  have  been  drawn  from  experi- 
mental inquiries  on  this  subject. 

I.  Vibrations  excited  in  solid  bodies,  may  be  transmitted  to  water 
without  much  loss  of  their  intensity  ;  although  not  with  the  same  rea- 
diness that  they  would  be  communicated  to  another  solid. 

II.  On  the  other  hand,  vibrations  excited  in  water  lose  something 
of  their  intensity  in  being  propagated  to  solids;  but  they  are  returned, 
as  it  were,  by  these  solids  to  the  liquid,  so  that  the  sound  is  more 
loudly  heard  in  the  neighbourhood  of  these  bodies,  than  it  would 
otherwise  have  been. 

III.  The  sonorous  vibrations  are  much  more  weakened  in  the  trans- 
mission of  solids  to  air ;  and  those  of  air  make  but  little  impression  on 
solids. 

IV.  Sonorous  vibrations  in  water  are  transmitted  but  feebly  to  air ; 
and  those  which  are  taking  place  in  air  are  with  difficulty  communi- 
cated to  water  ;  but  the  communication  is  rendered  more  easy,  by  the 
intervention  of  a  membrane  extended  between  them. 

The  application  of  these  conclusions,  in  the  Physiology  of  Hearing, 
will  be  presently  apparent. 

950.  It  is  on  the  Auditory  nerve  (commonly  termed  the  Portio 
Mollis  of  the  7th  pair),  that  the  sonorous  undulations  make  their  im- 
pression; but  we  invariably  find,  that  this  impression  is  made  through 
the  medium  of  a  liquid,  contained  in  a  cavity,  on  the  walls  of  which 
the  ultimate  branches  of  this  nerve  are  distributed.  The  simplest 
form  of  the  organ  of  Hearing,  such  as  we  find  in  some  Crustacea  and 
certain  Fishes,  consists  merely  of  a  cavity  excavated  in  the  solid 
framework  of  the  head ;  which  cavity  is  filled  with  liquid,  and  lined 
by  a  membrane  on  which  the  auditory  nerve  is  distributed.  These 
animals  are  inhabitants  of  the  water ;  and  the  sonorous  vibrations 
excited  in  this  medium,  being  communicated  to  the  solid  parts  of  the 
head,  will  be  by  them  again  transmitted  to  the  contained  fluid,  with- 
out much  diminution  of  their  intensity ;  according  to  principles  i.  and 


540  SIMPLEST  FORMS  OP  THE  ORGAN.— TYMPANUM. 

n.-— In  those  Crustacea,  however,  which  chiefly  inhabit  air,  as  well 
as  in  the  greater  number  of  the  class  of  Fishes,  we  find  the  auditory 
cavity  or  vestibule  no  longer  entirely  closed  ;  but  having  an  aperture 
on  its  external  side,  which  is  covered  in  by  a  membrane.  Here  the 
vibrations  of  the  liquid  within  the  cavity,  will  be  rnore  directly  excited 
by  those  of  the  surrounding  medium  ;  for  if  this  be  water,  it  will  pro- 
pagate its  undulations  into  the  cavity,  with  little  interruption  from 
the  membrane  stretched  across  its  mouth  ;  whilst,  if  it  be  air,  the 
interposition  of  this  very  membrane  will  greatly  assist  in  the  trans- 
mission of  the  vibrations  to  the  water  of  the  auditory  cavity,  accord- 
ing to  principle  iv.  In  most  animals,  which  have  the  organ  of 
hearing  constructed  upon  this  simple  plan,  the  force  of  the  vibrations 
of  the  fluid  within  the  cavity  is  increased  by  several  minute  stony 
concretions  (termed  otolithes),  which  are  suspended  in  it.  These 
act  according  to  principle  ii.  Some  traces  of  them  are  found  in  the 
higher  animals  ;  in  which  they  are  for  the  most  part  superseded,  how- 
ever, by  an  apparatus  better  adapted  to  augment  the  intensity  of  the 
sonorous  vibrations. 

951.  This  apparatus  consists,  in  all  Vertebrated  animals  above  the 
inferior  Reptiles,  of  the  tympanum  or  drum,  with  its  membrane  and 
chain  of  bones;  together  with,  in  the  Mammalia,  the  external  ear; 
which  is  adapted  to  direct  itself,  more  or  less  completely,  towards  the 
point  from  which  the  sonorous  vibrations  proceed,  and  to  give  them  a 
degree  of  preliminary  concentration.  The  tympanic  apparatus  is  inter- 
posed between  the  external  ear  and  the  membrane  covering  theybra- 
men  ovale,  which  is  the  entrance  to  the  real  auditory  cavity ;  and  its 
purpose  is  evidently  to  receive  the  sonorous  vibrations  from  the  air, 
and  to  transmit  them  to  that  membrane,  in  such  a  manner  that  the 
vibrations  thus  excited  in  the  latter  may  be  much  more  powerful  than 
they  would  be  if  the  air  acted  immediately  upon  it,  as  in  the  lower 
Vertebrata.  The  usual  condition  of  the  Membrana  Tympani  appears 
to  be  rather  lax ;  and,  when  in  this  condition,  it  vibrates  in  accord- 
ance with  grave  or  deep  tones.  By  the  action  of  the  tensor  tympani 
it  may  be  tightened,  so  as  to  vibrate  in  accordance  with  sharper  or 
higher  tones ;  but  it  will  then  be  less  able  to  receive  the  impressions 
of  deeper  sounds.  This  state  we  may  easily  induce  artificially,  by 
holding  the  breath,  and  forcing  air  from  the  throat  into  the  Eustachian 
tube,  so  as  to  make  the  membrane  bulge  out  by  pressure  from  within  ; 
or  by  exhausting  the  cavity  by  an  effort  at  inspiration,  with  the  mouth 
and  nostrils  closed,  which  will  cause  the  membrane  to  be  pressed 
inwards  by  the  external  air.  In  either  case,  the  hearing  is  imme- 
diately found  to  be  imperfect;  but  the  deficiency  relates  only  to  grave 
sounds,  acute  ones  being  heard  even  more  plainly  than  before.  There 
is  a  different  limit  to  the  acuteness  of  the  sounds,  of  which  the  ear 
can  naturally  take  cognizance,  in  diff*erent  persons.  If  the  sound  be 
so  high  in  pitch,  that  the  membrana  tympani  cannot  vibrate  in  unison 
with  it,  the  individual  will  not  hear  it,  although  it  may  be  loud  ;  and 
it  has  been  noticed  that  certain  individuals  cannot  hear  the  very  shrill 


SEMICIRCULAR  CANALS  ;   COCHLEA.— SENSE  OF  HEARING.     541 

tones  produced  by  particular  Insects,  or  even  Birds,  which  are  dis- 
tinctly audible  to  others. 

952.  Not  only  do  we  find  the  tympanic  apparatus  superadded,  in 
the  higher  forms  of  the  organ  of  Hearing,  but  also  the  Semicircular 
Canals,  and  the  Cochlea. — The  former  exist  in  all  Vertebrata,  save 
the  lowest  Fishes ;  and  in  nearly  every  case,  they  are  three  in  num- 
ber, and  lie  in  three  different  planes.  Hence  it  has  been  supposed, 
with  some  probability,  that  they  assist  in  producing  the  idea  of  the 
direction  of  sounds.  The  Cochlea  does  not  exist  at  all  in  Fishes  ;  and 
in  Reptiles  its  condition  is  quite  rudimentary.  In  Birds,  this  cavity 
is  more  completely  formed,  though  the  passage  is  nearly  straight 
instead  of  spiral ;  of  its  real  character,  however,  there  can  be  no  doubt, 
from  its  being  divided,  like  the  Cochlea  of  Man,  by  a  membranous 
partition,  on  which  the  ramifications  of  the  auditory  nerve  are  spread 
out.  This  appendage  has  been  supposed  to  be  the  organ,  that  enables 
us  to  judge  oii\ie  pitch  of  sounds;  an  idea  which  derives  some  con- 
firmation from  the  correspondence  between  the  development  of  the 
cochlea  in  different  animals,  and  the  variety  in  the  pitch  (or  length  of 
the  scale)  of  the  sounds,  which  it  is  important  that  they  should  hear 
distinctly,  especially  the  voices  of  their  own  kind. — That  the  Vesti- 
bule, with  the  passages  proceeding  from  it,  constitutes  the  true  organ 
of  hearing,  even  in  Man,  is  evident  from  the  fact,  that  when  (as  not 
unfrequently  happens)  the  tympanic  apparatus  has  been  entirely  de- 
stroyed by  disease,  so  as  to  reduce  the  organ  to  the  condition  of  that 
in  which  no  such  apparatus  exists,  the  faculty  of  Hearing  is  by  no 
means  abolished,  though  it  is  deadened. 

953.  The  faculty  of  Hearing,  like  other  senses,  may  be  very  much 
increased  in  acuteness  by  cultivation  ;  but  this  improvement  depends 
rather  upon  the  habit  of  attention  to  the  faintest  impressions  made 
upon  the  organ,  than  upon  any  change  in  the  organ  itself.  This  habit 
may  be  cultivated  in  regard  to  sounds  of  some  one  particular  class; 
all  others  being  heard  as  by  an  ordinary  person.  Thus,  the  watchful 
North  American  Indian  recognizes  footsteps,  and  can  even  distinguish 
between  the  tread  of  friends  and  foes  ;  whilst  his  white  companion, 
who  has  lived  among  the  busy  hum  of  cities,  is  unconscious  of  the 
slightest  sound.  Yet  the  latter  may  be  a  musician,  capable  of  dis- 
tinguishing the  tones  of  all  the  different  instruments  in  a  large  orches- 
tra, of  following  any  one  of  them  through  the  part  which  it  performs, 
and  of  detecting  the  least  discord  in  the  blended  effects  of  the  whole, 
— effects  which  would  be  to  the  unsophisticated  Indian  but  an  indis- 
tinct mass  of  sound.  In  the  same  manner,  a  person  who  has  lived 
much  in  the  country,  is  able  to  distinguish  the  note  of  every  species 
of  bird  that  lends  its  voice  to  the  general  chorus  of  nature;  whilst  the 
inhabitant  of  a  town  hears  only  a  confused  assemblage  of  shrill  sounds, 
which  may  impart  to  him  a  disagreeable  rather  than  a  pleasurable 
sensation. 

954.  In  all  continued  sounds  or  tones^  there  are  several  points  to  be 
attended  to.     In  the  first  place,  we  take  cognizance  of  their  pitch  ; 


542  OP  THE  SENSE  OF  SIGHT. 

which  depends  upon  the  number  of  vibrations  in  a  given  time, — the 
high  notes  being  produced  by  the  most  rapid  vibrations,  and  the  low 
notes  by  the  slowest.  The  ear  can  appreciate  tones  produced  by 
24,000  impulses  per  second  ;  the  pitch  of  which  is  about  four  octaves 
above  the  highest  F  of  the  piano-forte.  On  the  other  hand,  no 
sequence  of  vibrations  fewer  than  7  or  8  in  a  second,  can  produce  a 
continuous  tone ;  because  the  impression  left  by  each  impulse  has 
passed  away,  before  the  next  succeeds  ;  and  there  is  consequently  no- 
thing more  than  a  succession  of  distinct  beats. — The  strength  or  loud- 
ness of  musical  tones  depends  (other  things  being  equal)  on  the  force 
and  extent  of  the  vibrations,  communicated  by  the  sounding  body  to 
the  medium  which  propagates  them.  This  will  diminish,  however, 
with  distance ;  which  softens  loud  tones  by  lowering  the  intensity  of 
the  undulations,  as  a  consequence  of  their  more  extensive  diffusion. 
The  cause  of  the  differences,  in  the  timbre,  or  quality  of  musical  tones, 
— such,  for  instance,  as  those  which  exist  between  the  tones  of  a  flute, 
a  violin,  a  trumpet,  and  a  human  voice,  all  sounding  a  note  of  the 
same  pitch, — are  unknown :  but  they  probably  depend  upon  differ- 
ences of  form  in  the  undulations. — Our  ideas  of  the  direction  and 
distance  of  sounds,  are  for  the  most  part  formed  by  habit.  Of  the 
former  we  probably  judge  in  great  degree,  by  the  relative  intensity  of 
the  impressions  received  by  the  two  ears ;  though  we  may  form  some 
notion  of  it  by  a  single  ear,  if  the  idea  just  stated  as  to  the  use  of  the 
semicircular  canals  (§  952),  be  correct.  Of  the  distance  of  the  sound- 
ing body,  we  judge  by  the  intensity  of  the  sound,  comparing  it  with 
that  which  we  know  the  same  body  to  produce  when  nearer  to  us. 
The  Ear  may  be  deceived  in  this  respect,  as  w^ell  as  the  eye  ;  thus  the 
effect  of  a  full  band  at  a  distance  may  be  given  by  the  subdued  tones 
of  a  concealed  orchestra  close  by  us ;  and  the  Ventriloquist  produces 
his  deception,  by  imitating  as  closely  as  possible,  not  the  sounds 
themselves,  but  the  manner  in  which  they  would  strike  our  ears. 

6.   Of  the  Sense  of  Sight. 

955.  By  the  faculty  of  Sight,  we  are  made  acquainted,  in  the  first 
place,  with  the  existence  of  Light ;  and  by  the  medium  of  that  agent, 
we  take  cognizance  of  the  form,  size,  colour,  position,  &c.,  of  bodies 
that  transmit  or  reflect  it.  As  to  the  mode  in  which  luminous  im- 
pressions are  propagated  through  space,  philosophers  are  at  present 
undetermined  ;  and  the  question  is  of  no  physiological  importance, 
since  all  are  agreed  as  to  the  laws  which  regulate  their  transmission. 
These  laws,  which  will  be  found  at  large  in  any  Treatise  on  Natural 
Philosophy,*  may  be  briefly  stated  as  follows. 

I.  Light  travels  in  straight  lines,  so  long  as  the  medium  through 
which  it  passes  is  of  uniform  density. 

II.  When  the  rays  of  light  pass  from  a  rarer  medium  into  a  denser 

•  See  Dr.  Golding  Bird's  Manual,  Chap.  XXII. 


LAWS  OF  TRANSMISSION  OF  LIGHT.  543 

one,  they  are  refracted  towards  a  line  drawn  perpendicularly  to  the 
surface  they  are  entering. 

III.  When  the  rays  of  light  pass  from  a  denser  medium  into  a  rarer 
one,  they  are  refractedyrom  the  perpendicular. 

IV.  When  rays  proceeding  from  the  several  points  of  a  luminous 
object,  at  a  distance,  fall  upon  a  double  convex  lens,  they  are  brought 
to  a   focus   upon  the   other 

side  of  it;  in  such  a  man-  Fig.iso. 

ner    that    an   inverted   pic-  

ture  of  the  object  is  formed  c 3^==::^ ^^-^^^^^ 

upon  a  screen,  placed  in  the  "^^S^^^^^iXS^?'''^^"^-^^--^ 

proper  position  to  receive  it.      ^ <^^<^^'jCr^'C  ^^^^ 

Thus  in  Fig.  150,  A  B  is  \^^^^4^^^^^<>Z 

the    object,  and   E    F   the  ^  ^^     ^-— ^^I::^ 

lens ;  the  rays  issuing  from 
the  two  extremities  and  the 

centre  of  the  object,  are  brought  to  a  corresponding  focus  at  a  less 
distance  on  the  other  side  of  it,  so  as  to  form  a  distinct  picture  ;  but 
as  the  rays  from  a  are  brought  to  a  focus  at  d,  and  those  from  b  at  c, 
the  picture  will  be  inverted. 

v.  The  further  the  object  is  removed  from  the  lens,  the  nearer  will 
the  picture  be  brought  to  it,  and  the  smaller  will  it  be. 

VI.  If  the  screen  be  not  held  precisely  in  the  focus  of  the  lens,  but 
a  little  nearer,  or  further  off,  the  picture  will  be  indistinct  ;  for  the 
rays  which  form  it  will  either  not  have  met,  or  they  will  have  crossed 
each  other. 

956.  The  Eye,  in  its  most  perfect  form — such  as  it  possesses  in 
Man  and  the  higher  animals, — is  an  optical  instrument  of  wonderful 
completeness;  designed  to  form  an  exact  picture  of  surrounding 
objects,  upon  the  Retina  or  expanded  surface  of  the  Optic  nerve,  by 
which  the  impression  is  conveyed  to  the  brain.  The  rays  of  light, 
which  diverge  from  the  several  points  of  any  object,  and  fall  upon  the 
front  of  the  cornea,  are  refracted  by  its  convex  surface,  whilst  passing 
through  it  into  the  eye,  and  are  made  to  converge  slightly.  They  are 
brought  more  closely  together  by  the  crystaline  lens,  which  they 
reach  after  passing  through  the  pupil ;  and  its  refracting  influence, 
together  with  that  produced  by  the  vitreous  humour,  is  such  as  to 
cause  the  rays,  that  issued  from  each  point,  to  meet  in  a  focus  on  the 
retina.  In  this  manner,  a  complete  inverted  image  is  formed,  as 
shown  in  Fig.  151  ;  which  represents  a  vertical  section  of  the  eye, 
and  the  general  course  of  the  rays  in  its  interior.  As  in  the  preceding 
figure,  the  rays  which  issue  from  the  point  a  are  brought  to  a  focus 
at  D ;  whilst  those  diverging  from  b  are  made  to  converge  upon  the 
retina  at  c.  The  Retina,  which  is  itself  so  thin  as  to  be  nearly  trans- 
parent, is  spread  over  the  layer  of  black  pigment,  which  lines  the 
choroid  coat.  The  purpose  of  this  is  evidently  to  absorb  the  rays  of 
light  that  form  the  picture,  immediately  after  they  have  passed  through 
the  retina ;  in  this  manner,  they  are  prevented  from  being  reflected 


544        OF  THE  EYE  AS  AN  OPTICAL  INSTRUMENT. 

from  one  part  of  the  interior  of  the  globe  to  another ;  which  would 
cause  great  confusion  and  indistinctness  in  the  picture.     Hence  it  is 

that,  in  those  albino  individuals 
'P'^g'^^^'  (both  of  the   Human   race,   and 

among    the    lower    animals),    in 
whose   eyes   this  pigment  is   de- 
ficient,   vision   is   extremely   im- 
perfect, except  in  a  very  feeble 
light ;  for  the   vascularity  of  the 
choroid  and  iris  is  such,  as  to  give 
to  these  membranes  a  bright  red 
hue,  which  enables  them  powerfully  to  reflect  the  light  that  reaches 
the  interior  of  the  eye,  when  they  are  not  prevented  from  doing  so  by 
the  interposition  of  the  pigmentary  layer. 

957.  The  Eye  is  so  constructed  as  to  avoid  certain  errors  and 
defects,  to  which  all  ordinary  optical  instruments  are  liable.  One  of 
these  imperfections,  termed  spherical  aberration,  results  from  the  fact, 
that  the  rays  of  light,  passing  through  a  convex  lens  whose  curvature 
is  circular,  are  not  all  brought  to  their  proper  foci;  those  which  have 
passed  through  the  exterior  of  the  lens  being  made  to  converge  sooner 
than  those  which  have  traversed  its  central  portion.  The  result  of 
this  imperfection  is,  that  the  image  is  deficient  in  clearness,  unless 
only  the  central  part  of  the  lens  be  employed. — The  other  source  of 
imperfection  is  what  is  termed  chromatic  aberration;  and  it  results 
from  the  unequal  degree  in  which  the  differently  coloured  rays  are 
refracted,  so  that  they  are  brought  to  a  focus  at  different  points.  The 
violet  rays,  being  the  most  refrangible,  are  soonest  brought  to  a  focus; 
and  the  red  being  the  least  refrangible,  have  their  focus  at  the  greatest 
distance  from  the  lens.  Hence  it  is  impossible  to  obtain  an  image  by 
an  ordinary  lens,  in  which  the  colours  of  the  object  are  accurately 
represented ;  for  the  foci  of  its  differently  coloured  portions  will  be 
different ;  and  its  white  rays  will  be  decomposed,  so  that  the  outlines 
will  be  surrounded  by  coloured  fringes. — The  Optican  is  enabled  to 
correct  the  effects  of  these  aberrations,  by  combining  lenses  of  diflfer- 
ent  densities  and  curvatures ;  so  arranged  as  to  correct  each  others' 
errors,  without  neutralizing  the  refractive  power.  This  is  precisely 
the  plan  adopted  in  the  construction  of  the  Eye  ;  which,  when  per- 
fectly formed,  and  in  a  healthy  state,  forms  an  accurate  picture  of 
the  object  upon  the  retina,  free  from  either  spherical  or  chromatic 
aberration.  This  is  effected  by  the  combination  of  humors  of  differ- 
ent densities,  having  curvatures  precisely  adapted  to  the  required 
purpose. 

958.  There  are  certain  variations,  however,  in  the  conformation  of 
the  Eye,  which  diminish  the  perfection  of  its  rfesult.  Thus  the  Cornea 
may  be  too  convex,  and  the  whole  retractive  power  too  great;  so  that 
the  image  of  an  object  at  a  moderate  distance  is  formed  in  front  of 
the  retina,  instead  of  upon  it.  When  this  is  the  case,  a  distinct  image 
can  only  be  formed,  by  bringing  the  object  nearer  to  the  eye ;  the 


OP  THE  EYE  AS  AN  OPTICAL  INSTRUMENT.  545 

effect  of  which  will  be,  to  throw^  the  picture  further  back.  Such  an 
eye  is  said  to  be  myopic,  or  short-sighted  ;  and  its  imperfection  may- 
be corrected  by  placing  a  concave  lens  in  front  of  the  cornea,  of  a 
curvature  adapted  to  neutralize  what  is  superfluous  in  the  convexity 
of  the  latter. — On  the  other  hand,  if  the  cornea  be  too  flat,  and  the 
refractive  power  of  the  humors  be  too  low,  the  convergent  rays  pro- 
ceeding from  an  object  at  a  moderate  distance  will  not  meet  upon  the 
retina,  but  behind  it  (if  they  were  allowed  to  pass  on);  consequently, 
the  picture  is  indistinct ;  and  it  can  only  be  made  clear,  either  by 
withdrawing  the  object  to  a  greater  distance,  which  will  bring  the 
focus  of  the  eye  nearer  to  its  front,  or  by  interposing  a  convex  lens 
to  increase  the  refractive  power  of  the  eye.  Such  a  condition  is 
termed  presbyopic  (from  its  being  common  in  aged  persons),  or  long- 
sighted. It  may  proceed  to  such  an  extent,  that  not  even  the  removal 
of  the  object  to  any  distance  can  permit  the  formation  of  a  distinct 
picture ;  so  that  the  assistance  of  a  convex  lens  must  be  obtained, 
even  to  see  remote  objects  clearly;  though  a  less  degree  of  convexity 
will  be  required  than  for  the  clear  vision  of  nearer  objects.  This  state 
is  particularly  well-marked  after  the  operation  for  cataract ;  for  the 
removal  of  the  crystaline  lens  so  greatly  diminishes  the  refractive 
power  of  the  eye,  as  to  render  necessary  the  assistance  of  convex 
lenses  of  high  curvature. 

959.  The  power,  by  which  a  healthy  well-formed  eye  can  accom- 
modate itself  to  the  distinct  vision  of  objects  at  varying  distances,  is 
a  very  remarkable  one ;  and  its  rationale  is  not  yet  properly  under- 
stood. According  to  the  laws  already  stated  (§  955,  V.  and  VI.), 
the  picture  of  a  near  object  can  only  be  distinct  when  formed  more 
remotely  from  the  lens  than  the  picture  of  a  distant  object.  Conse- 
quently when  the  eye,  that  has  been  looking  at  a  distant  object,  and 
has  seen  it  clearly,  is  turned  to  a  near  object,  a  distant  picture  of  the 
latter  cannot  be  formed  without  some  alteration,  either  in  the  distance 
between  the  cornea  and  the  retina,  or  in  the  curvature  of  its  refractive 
surfaces.  Of  the  mode  in  which  this  adjustment  is  made,  however, 
nothing  is  certainly  known  ;  the  minuteness  of  the  requisite  amount 
of  alteration  being  such  as  to  prevent  its  precise  seat  from  being  de- 
termined. 

960.  The  various  humors  and  containing  membranes  of  the  Eye, 
thus  answer  the  purpose  of  a  most  delicate  and  self-adjusting  Optical 
instrument ;  the  sole  part,  which  is  immediately  concerned  in  the  act 
of  sensation,  being  the  Retina,  or  net-like  expansion  of  the  Optic 
nerve,  which  lies  between  the  black  pigment  and  the  vitreous  humor. 
It  is  in  this  structure  that  the  presence  of  cells  at  the  peripheral  as 
well  as  the  central  extremities  of  the  afferent  nerves  (§  381),  may  be 
most  clearly  demonstrated.  They  can  scarcely  be  distinguished,  in 
many  animals,  from  the  cells  of  the  vesicular  matter  of  the  brain  ;  and, 
like  the  latter,  they  lie  in  the  midst  of  a  plexus  of  capillary  blood- 
vessels, which  supplies  the  materials  requisite  for  their  growth  and 
activity.     For  the  maintenance  of  the  due  nutrition  of  this  organ,  it  is 

35 


646  VISUAL  PERCEPTIONS. 

requisite  that  it  should  be  occasionally  called  into  use.     If  its  func- 
tional power  be  destroyed,  by  opacity  of 
^'s- 152.  the  anterior  portion  of  the  eye,  the  nutri- 

tion of  the  retina  and  optic  nerve  suffers 
to  such  a  degree  that  these  parts  cease 
after  a  time  to  exhibit  their  characteristic 
structure  ; — thus  showing  that  the  general 
rules  already  stated  (Chap.  VII.)  in  re- 
gard to  the  connection  between  the  func- 
tional activity,  and  the  due  nutrition  of 
tissues  and  organs,  hold  good  with  re-> 
spect  to  the  Nervous  structure. — The 
mode  in  which  the  vesicular  layer  of  the 
retina  comes  into  relation  with  the  net- 
work of  nerve-fibres,  of  which  it  chiefly 

Distribution  of  Capillaries  invascu-  •   *.       i,  t        i.  u  i        i 

lar  layer  of  Retina.  consists,  has  not  yet  bccn  clearly  ascer- 

tained. 

961.  The  picture  of  external  objects,  which  is  formed  upon  the 
Retina,  closely  resembles  that  which  we  see  in  a  Camera  Obscura.  It 
represents  the  outlines,  colours,  lights  and  shades,  and  relative  posi- 
tions, of  the  objects  before  us  ;  but  these  do  not  necessarily  convey  to 
the  mind  the  knowledge  of  their  real  forms,  characters,  or  distances. 
The  perception  of  the  latter,  as  already  remarked  (§  936),  is  a  mental 
process ;  and  it  may  be  intuitive,  or  acquired, — the  latter,  it  w^ould 
seem,  being  the  general  condition  of  the  function  in  Man,  the  former 
in  the  lower  animals.  The  Infant  is  educating  his  perceptive  powers, 
long  before  any  indications  present  themselves  of  the  exercise  of 
higher  mental  faculties.  By  the  combination,  especially  of  the  sen- 
sations of  sight  and  touch,  he  is  learning  to  judge  of  the  surfaces  of 
objects  as  they  feel,  by  the  appearance  they  present, — to  form  an  idea 
of  their  distance,  by  the  mode  in  which  his  eyes  are  directed  towards 
them, — and  to  estimate  their  size,  by  combining  the  notions  obtained 
through  the  picture  on  the  retina,  with  those  he  acquires  by  the  move- 
ment of  his  hands  over  their  different  parts. — A  simple  illustration 
will  show  how  closely  the  ideas  excited  by  the  two  sets  of  sensations, 
are  blended  in  our  minds.  The  idea  of  smoothness  is  one  w^hich  has 
reference  to  the  touch  ;  and  yet  it  constantly  occurs  to  us,  on  looking 
at  a  surface  which  reflects  light  in  a  particular  manner.  On  the  other 
hand,  the  idea  of  polish  is  essentially  visual,  having  reference  to  the 
reflection  of  light  from  the  surface  of  the  object;  and  yet  it  would 
occur  to  us  from  the  sensation  conveyed  through  the  touch,  even  in 
the  dark. 

962.  That  this  sort  of  combination  is  not  intuitive  in  Man,  but  is 
the  result  of  experience,  is  evident  from  the  numerous  observations 
made  upon  those,  who  had  acquired  the  sense  of  Sight  for  the  first 
time,  after  long  familiarity  with  the  characters  of  objects  as  perceived 
through  the  Touch.  Thus  a  boy  of  four  years  old,  upon  w^hom  the 
operation  for  congenital  cataract  had  been  very  successfully  performed, 


ERECT  AND  SINGLE  VISION.  547 

continued  to  find  his  way  about  his  father's  house,  rather  hy  feeling 
with  his  hands,  as  he  had  been  formerly  accustomed  to  do,  than  by 
his  newly-acquired  sense  of  Sight;  being  evidently  perplexed,  rather 
than  assisted,  by  the  sensations  which  he  derived  through  it.  But 
when  learning  a  new  locality,  he  employed  his  sight,  and  evidently 
perceived  the  increase  of  facility  which  he  derived  from  it.  Among 
the  many  interesting  particulars  recorded  of  the  youth,  on  whom 
Cheselden  operated  with  equal  success,  it  is  mentioned  that,  although 
perfectly  familiar  with  a  dog  and  a  cat  by  feeling  them,  and  quite 
able  to  distinguish  between  them  by  his  sight,  he  was  long  before  he 
associated  his  visual  with  his  tactual  sensations,  so  as  to  be  able  to 
name  either  animal  by  sight  alone. — The  question  was  put  by  the 
celebrated  Locke,  whether  a  person  born  blind,  who  was  able  by 
his  touch  to  distinguish  a  cube  from  a  sphere,  would,  on  suddenly 
obtaining  his  sight,  be  able  to  recognize  each  by  the  latter  sense ; 
the  reply  was  given  in  the  negative;  and  the  experience  of  the  cases 
just  referred  to,  as  well  as  of  many  others,  fully  justifies  such  an 
answer. 

963.  Still  there  are,  even  in  Man,  certain  intuitive  perceptions, 
which  aflford  great  assistance  in  the  formation  of  ideas  regarding  ex- 
ternal objects,  through  the  visual  sense.  And  the  first  of  these  is  the 
power  by  which  we  recognize  their  erect  position,  notwithstanding 
the  inversion  of  the  image  upon  the  retina.  This  is  certainly  not  a 
matter  of  experience  ;  nor  is  it  capable  of  explanation  (as  some  have 
thought)  by  a  reference  to  the  direction  in  which  the  rays  fall  upon 
the  retina.  It  is  the  mind  which  rectifies  the  inversion  ;  and,  as 
already  remarked,  it  is  just  as  difficult  to  understand,  how  the  inverted 
image  on  the  retina  should  be  taken  cognizance  of  by  the  mind  at  all, 
as  it  is  to  comprehend  how  it  should  be  thus  rectified.  In  fact,  there 
is  no  real  connection  whatever,  between  the  inversion  of  the  image 
upon  the  retina,  and  that  wrong  perception  of  external  objects,  which 
some  have  thought  to  be  its  necessary  consequence.  Any  distortion 
of  the  picture,  giving  a  wrong  view  of  the  relative  positions  of  the 
objects  represented,  v^ould  be  attended  with  a  different  result. — The 
same  may  be  said  of  the  cause  of  the  singleness  of  the  sensation  per- 
ceived by  the  mind,  although  an  image  is  formed  upon  the  retina  of 
each  eye, — of  those  objects,  at  least,  which  lie  in  the  field  of  vision 
that  is  common  to  both.  This  blending  of  the  pictures  formed  upon 
the  two  retinae  into  a  single  perception,  appears  to  be,  in  part  at  least, 
the  effect  of  habit.  For  when  the  images  do  not  fall  upon  the  parts  of 
the  two  retinae,  which  are  accustomed  to  act  together,  double  vision  is 
the  result.  Thus  if,  when  looking  steadily  at  an  object,  we  press  one- 
of  the  eyeballs  sideways  with  the  finger,  we  see  two  representations 
of  the  object ;  and  the  same  thing  frequently  occurs  as  a  result  of  an 
affection  of  the  nerves  or  muscles  of  one  or  both  eyes,  (as  inordinary 
strabismus  or  squinting,)  or  from  some  change  in  the  nervous  centres, 
as  in  various  disorders  of  the  Encephalon,  and  in  intoxication.  If  this 
condition  should  be  permanent,  however,  we  usually  find  that  the  in- 


548  COMBINATION  OF  PICTURES  IN  TWO  EYES. 

dividual  becomes  accustomed  to  the  double  images,  or  rather  ceases 
to  perceive  that  they  are  double ;  probably  because  the  mind  becomes 
habituated  to  receive  the  impressions  from  the  two  parts  of  the  retina, 
which  now  act  together.  And  if,  after  the  double  vision  has  passed 
away,  the  conformity  of  the  tw^o  eyes  be  restored  (as  by  the  operation 
for  the  cure  of  squinting)  there  is  double  vision  for  some  little  time, 
although  the  two  parts  of  the  retina,  which  originally  acted  together, 
are  now  brought  into  their  pristine  position. 

964.  But  the  images  thus  combined  are  far  from  being  identical; 
and  one  of  the  most  remarkable  of  all  our  intuitive  perceptions  is  that 
by  wdiich  they  are  reconciled  and  combined,  and  are  caused  to  give 
rise  to  an  idea,  that  differs  essentially  from  either  image.  No  near 
object  can  be  seen  by  the  two  eyes  in  the  same  manner ;  of  this  the 
reader  may  easily  convince  himself,  by  holding  up  a  thin  book  in  such 
a  manner  that  its  back  shall  be  in  a  line  with  the  nose,  and  at  a  mo- 
derate distance  from  it;  and  by  looking  at  the  book  first  with  one 
eye,  and  then  w^ith  the  other.  He  will  find  that  he  gains  a  different 
view  of  the  object  with  each  eye,  when  used  separately  ;  so  that  if  he 
were  to  represent  it  as  he  actually  sees  it  under  these  circumstances 
he  would  have  two  perspective  delineations  differing  from  one  another, 
because  draw^n  from  different  points.  But  on  looking  at  the  object 
with  the  two  eyes  conjointly,  there  is  no  confusion  between  these  pic- 
tures; nor  does  the  mind  dwell  upon  either  of  them  singly;  but  the 
union  of  the  two  intuitively  gives  us  the  idea  of  a  solid  projecting 
body, — such  an  idea  as  we  could  only  have  otherwise  acquired  by  the 
exercise  of  the  sense  of  touch.  That  this  is  really  the  case,  has  been 
proved  by  experiments  with  a  very  ingenious  instrument,  the  Stereo- 
scope, invented  by  Prof.  Wheatstone ;  which  is  so  contrived  as  to 
bring  to  the  two  eyes,  by  reflection  from  mirrors,  two  different  pic- 
tures, such  as  would  be  accurate  representations  of  a  solid  object,  as 
seen  by  the  two  eyes  respectively.  When  the  arrangement  is  such, 
as  to  bring  the  images  of  these  pictures  to  those  parts  of  the  retinae 
which  would  have  been  occupied  by  the  images  of  the  solid  (supposing 
that  to  have  been  before  the  eyes),  the  mind  will  perceive,  not  one  or 
other  of  the  single  representations  of  the  object,  nor  a  confused  union 
of  the  tW'O,  but  a  body  projecting  in  reliefs  the  exact  counterpart  of 
that  from  which  the  drawings  were  made. — Thus  the  combination  of 
the  two  pictures  and  the  perception  of  an  object  different  from  either 
of  them,  is  effected  by  a  mental  process  of  an  instinctive  kind  ;  of  the 
nature  of  which  we  know  nothing  further. 

965.  When  two  pictures,  representing  dissimilar  objects,  are  pro- 
jected upon  the  retinae  of  the  tw^o  eyes  by  means  of  the  Stereoscope, 
the  result  is  a  curious  one.  The  mind  perceives  only  one  of  them, 
the  other  being  completely  excluded  for  a  time;  but  it  commonly 
happens  that,  after  one  has  been  seen  for  a  short  period,  the  other 
begins  to  attract  attention  and  takes  its  place,  the  first  entirely  dis- 
appearing; so  that  there  is  no  confusion  or  intermingling  of  images, 
except  at  the  moment  of  change.     The  Will  may  determine,  to  a 


ESTIMATION  OF  DISTANCE  OF  OBJECTS.  549 

certain  extent,  which  object  shall  be  seen ;  but  not  entirely ;  for  if 
one  picture  be  more  illuminated  than  the  other,  it  will  be  seen  during 
a  larger  proportion  of  the  time. — An  interesting  variation  of  this  ex- 
periment may  be  made,  without  the  aid  of  the  Stereoscope,  by  holding 
a  piece  of  blue  glass  before  one  eye,  and  a  piece  of  yellow  glass 
before  the  other.  The  result  will  be,  not  that  everything  will  be  seen 
of  a  green  colour,  but  that  the  surrounding  objects  will  be  seen  alter- 
nately blue  and  yellow; — or  sometimes  the  field  of  vision  will  be 
blue,  spotted  with  yellow  ;  alternating  with  yellow  spotted  with  blue. 
Thus,  when  we  have  two  dissimilar  objects  before  the  eyes,  our  at- 
tention cannot  be  kept  upon  either,  to  the  exclusion  of  the  other,  but 
is  alternately  and  involuntarily  directed,  either  in  part  or  completely, 
to  one  and  the  other. 

966.  Our  idea  of  the  distance  of  near  objects  is  evidently  acquired 
from  experience;  and  is  suggested  by  the  muscular  sensations,  which 
are  produced  by  the  contraction  of  the  adductor  muscles  of  the  eyes. 
When  we  direct  our  eyes  towards  a  near  object,  a  certain  degree  of 
convergence  takes  place  between  their  axes;  the  degree  increasing  as 
the  distance  between  the  object  and  the  eyes  diminishes;  and  vice 
versa.  We  instinctively  interpret  the  sensations  thus  produced,  in 
such  a  manner  as  to  be  able  to  compare,  with  great  accuracy,  the  rela- 
tive distances  of  two  objects,  that  are  not  remote  from  the  eyes.  This 
intuition,  however,  is  evidently  one  of  the  acquired  kind;  as  may  be 
seen  by  watching  the  actions  of  an  infant,  or  of  a  person  who  has 
recently  become  possessed  of  Vision.  When  an  object  is  held  before 
the  eyes  and  an  attempt  is  made  to  grasp  it,  the  manner  in  which  the 
attempt  is  made  clearly  shows,  that  there  is  no  power  of  forming  a 
precise  idea  of  its  situation,  such  as  that  which  exists  in  many  of  the 
lower  animals  from  their  first  entrance  into  the  world  (§  938).  The 
impressions  made  upon  the  eyes  have  to  be  corrected  by  those  received 
through  the  touch,  before  the  power  of  judging  of  distance  is  accom- 
plished. How  much  this  power  depends  upon  the  conjoint  use  of 
both  eyes,  is  evident  from  the  difiSculty  with  which  any  actions,  that 
require  an  exact  appreciation  of  distance,  are  performed  by  those  who 
have  lost  the  sight  of  one  eye,  until  they  have  acquired  new  modes  of 
judging  of  it. 

967.  In  regard  to  remote  objects,  we  have  not  the  same  guide  ; 
since  the  convergence  of  the  eyes,  in  viewing  them,  is  so  slight  that 
the  axes  are  virtually  parallel.  Our  judgment  of  their  distance  is 
chiefly  founded  upon  their  apparent  size,  if  their  actual  size  be  known 
to  us  ;  and  also  upon  the  extent  of  ground,  which  we  see  to  intervene 
between  ourselves  and  the  object.  But  if  we  do  not  know  their 
actual  size,  and  are  so  situated  that  we  cannot  estimate  the  interven- 
ing space,  we  form  our  judgment  chiefly  from  the  greater  or  less  dis- 
tinctness of  their  colour  and  outline.  Hence  our  idea  of  it  will  be 
very  much  affected  by  varying  states  of  the  atmosphere ;  a  slight 
haziness  increasing  the  apparent  distance  ;  whilst  a  peculiarly  clear 
state  of  the  air  will  seem  to  cause  remote  objects  to  approach  much 


550  CHANGES  IN  SIZE  OF  PUPIL. 

more  closely.  This  want  of  convergence  between  the  axes  of  the 
two  eyes,  has  the  further  effect  of  causing  the  pictures  upon  the  two 
retinae  to  be  nearly  identical ;  and  consequently  the  idea  of  projection 
is  not  so  strongly  excited;  nor  are  we  able  to  distinguish  with  the 
same  certainty  between  a  well-painted  picture,  in  which  the  lights 
and  shades  are  preserved,  and  the  objects  themselves  in  relief. 

968.  Our  notion  of  the  size  of  an  object  is  closely  connected  with 
that  of  its  distance.  It  is  founded  upon  the  dimensions  of  the  picture 
projected  on  the  retina;  and  the  dimensions  of  this  picture  will  vary, 
according  to  the  laws  of  optics,  (§  955,)  inversely  as  the  distance, — 
being,  for  example,  twice  as  great  when  the  object  is  viewed  at  the 
distance  of  one  foot,  as  when  it  is  carried  to  the  distance  of  two  feet. 
Where  we  know  the  relative  distances  of  two  objects,  the  estimation 
of  their  real  comparative  sizes  from  their  apparent  sizes,  is  easily 
effected  by  a  simple  process  of  mind;  but  this  is  not  the  case,  when 
we  only  guess  at  their  distances :  and  our  estimate  of  the  size  of 
objects,  even  moderately  remote,  is  as  much  affected  by  states  of  the 
atmosphere  as  that  of  their  distance, — the  one  being,  in  fact,  propor- 
tional to  the  other.  Thus  a  slight  mist,  which  gives  the  idea  of  in- 
creased distance,  will  also  augment  the  apparent  size  ;  because,  in 
order  that  an  object  two  miles  off  should  produce  a  picture  upon  the 
retina  of  the  same  extent  with  that  made  by  an  object  one  mile  off, 
it  must  have  double  the  dimensions.  It  is  evident  that  our  perception 
of  the  sizes  of  objects  must  be  acquired  by  experience,  in  the  same 
manner  as  that  of  their  distance  has  been  shown  to  be. 

969.  We  have  now  to  consider  briefly  some  other  phenomena  of 
Vision,  in  which  the  acts  of  Mind,  that  have  been  just  alluded  to,  do 
not  participate. — The  contraction  of  the  Pupil,  under  the  stimulus  of 
light,  seems  to  be  affected  by  a  sphincter  muscle,  which  surrounds 
the  orifice,  and  which  is  put  in  action  by  a  branch  of  the  third  pair  of 
nerves.  This  is  an  action  with  which  the  will  has  nothing  to  do  ;  and 
it  takes  place  entirely  without  our  consciousness.  Although  it  is  due 
to  the  stimulus  of  light,  yet  there  is  reason  to  believe  that  the  con- 
sciousness of  the  presence  of  light  is  not  requisite ;  and  that  it  is, 
therefore,  a  purely  reflex  action.  The  optic  nerve  seems  to  be  the 
channel  through  which  the  impression  is  conveyed  to  the  nervous 
centres  ;  and  the  third  pair  is  that  through  which  the  motor  impulse 
is  conveyed  to  the  iris.  But  there  is  some  ground  for  the  idea,  that 
the  fifth  pair  may  in  some  degree  convey  the  requisite  stimulus,  when 
the  optic  nerve  has  been  divided.  How  far  the  dilatation  of  the 
pupil  is  a  muscular  action,  or  merely  one  which  results  from  the  elas- 
ticity of  the  tissue  of  the  iris,  when  the  sphincter  is  relaxed,  has  not 
been  clearly  ascertained  ;  the  latter  is  probably  the  case,  a  perma- 
nently dilated  state  of  the  pupil  being  usually  seen  in  cases  where, 
from  any  cause,  it  is  not  affected  by  the  stimulus  of  light.  The  con- 
traction of  the  pupil  is  evidently  destined  to  exclude  from  the  interior 
of  the  eye,  such  an  amount  of  light  as  would  be  injurious  to  it ;  whilst 
its  dilatation  in  opposite  circumstances  admits  the  greatest  possi-- 


PERCEPTION  OF  COLOURS.  551 

ble  number  of  rays.  There  is  a  contraction  of  the  pupils,  however, 
which  takes  place  without  any  change  in  the  amount  of  light.  This 
occurs  when  the  two  eyes  are  made  to  converge  strongly  upon  any 
object  brought  very  near  them  ;  and  its  purpose  appears  to  be,  to 
prevent  the  rays  from  entering  the  eye  at  such  a  wide  angle  as  would 
render  it  impossible  for  them  to  be  all  brought  to  their  proper  foci, 
and  would  thus  produce  an  indistinct  image. 

970.  In  the  use  of  the  Eye,  like  that  of  the  Ear,  there  is  a  ten- 
dency to  blend  into  one  continuous  image  a  succession  of  luminous 
impressions  made  at  short  intervals  ;  upon  which  fact  depend  a  num- 
ber of  cuVious  optical  illusions.  The  length  of  the  greatest  interval 
that  can  elapse  without  an  interruption  of  the  presence  of  the  image, 
(in  other  words  the  duration  of  the  visual  impression,)  may  be  mea- 
sured by  causing  aluminous  object  to  whirl  round,  and  by  ascertain- 
ing the  longest  period  that  may  be  allowed  for  each  revolution, 
consistently  with  the  completeness  of  the  circle  of  light  thus  formed. 
By  experiments  of  this  kind,  the  time  has  been  found  to  vary,  in  dif- 
ferent individuals,  or  in  different  states  of  the  same  individual,  from 
about  l-4th  to  1-lOth  of  a  second  :  that  is,  the  impression  must  be 
repeated  from  four  to  ten  times  in  each  second,  to  insure  the  continu- 
ousness  of  the  image. 

971.  The  impressions  of  variety  of  colour^  are  produced  by  the 
differently  coloured  rays,  which  objects  reflect  or  transmit  to  the  eye. 
It  is  curious  that  some  persons,  whose  sight  is  perfectly  good  for  forms, 
distances,  &c.,  are  unable  to  discriminate  colours.  This  curious  affec- 
tion has  received  the  name  of  Daltonism,  from  the  circumstance  that 
the  celebrated  Dalton  was  an  example  of  it.  There  are  numerous 
modifications  of  it;  the  want  of  power  to  discriminate  colour  being  total 
in  some,  whilst  in  others  it  extends  only  to  certain  shades  of  colour, 
or  to  the  complementary  colours. 

972.  When  the  retina  has  been  exposed  for  some  time  to  a  strong 
impression  of  some  particular  kind,  it  seems  less  susceptible  of  feebler 
impressions  of  the  same  kind;  thus  if  we  look  at  any  brightly  luminous 
object,  and  then  turn  our  eyes  upon  a  sheet  of  paper,  we  shall  per- 
ceive a  dark  spot  upon  it, — the  portion  of  the  retina,  which  had  receiv- 
ed the  brighter  image,  not  being  affected  by  the  fainter  one. — Again, 
when  the  eyes  have  received  a  strong  impression  from  a  coloured 
object,  the  spot  which  is  seen  when  the  eyes  are  directed  upon  a 
white  surface  exhibits  the  complementary  colour ;  for  the  retina  has 
been  so  strongly  affected  in  the  part  that  originally  received  the  image, 
by  its  vivid  hue,  that  it  does  not  perceive  the  fainter  hue  of  the 
same  kind  in  the  object  to  which  it  is  then  turned,  and  it  is  impressed 
only  by  the  remaining  rays  forming  the  complementary  colours. 
This  explanation  applies  to  the  phenomena  of  the  coloured  shadows 
which  are  often  seen  at  sunset,  and  of  those  which  may  be  seen  in  a 
room  whose  light  enters  through  coloured  glass  or  drapery.  For  if  the 
prevailing  light  be  of  one  colour, — orange  or  red  for  instance, — the 
eye  will  not  take  cognizance  of  that  colour  in  the  faint  light  of  the 


552  OF  THE  VOICE  AND  SPEECH. 

shadows  ;  and  will  see  only  its  complement,  blue  or  green.  If  the 
shadow  be  viewed  through  a  tube,  in  such  a  manner  that  the  general 
coloured  ground  is  excluded,  it  presents  the  ordinary  tint. 


CHAPTER  XIV. 


OF  THE  VOICE,  AND  SPEECH. 


973.  There  is  one  particular  application  of  Muscular  power  in  Man, 
which  deserves  special  consideration,  as  being  that  by  which  he  effects 
his  most  complete  and  intimate  communication  with  his  fellows ; — 
that,  namely,  by  which  his  organ  of  Voice  is  put  into  action.  In  all 
air-breathing  Vertebrata,  the  production  of  sound  depends  upon  the 
passage  of  air  through  a  certain  portion  of  the  respiratory  tubes;  which 
is  so  constructed  as  to  set  it  in  vibration,  as  it  passes  forth  from  the 
lungs. — In  Reptiles,  the  vibrating  apparatus  is  situated  at  the  point, 
where  the  trachea  opens  into  the  front  of  the  pharynx ;  it  is  of  very 
simple  construction,  however,  being  only  composed  of  a  slit  bounded 
by  two  contractile  lips;  and  few  of  the  animals  of  this  class  can  pro- 
duce any  other  sound  than  a  hiss,  which,  owing  to  the  great  capacity 
of  their  lungs,  is  often  very  much  prolonged. — In  Birds,  the  situation 
of  the  vocal  organ  is  very  different.  The  trachea  opens  into  the  front 
of  the  pharynx,  as  in  Reptiles,  by  a  mere  slit ;  the  borders  of  which 
have  no  other  movement  than  that  of  approaching  one  another,  so  as 
to  close  the  aperture  when  necessary.  This  appears  to  be  the  instru- 
ment for  regulating  the  ingress  and  egress  of  air,  in  conformity  with 
the  wants  of  the  respiratory  function.  The  vocal  larynx  of  Birds  is 
situated  at  the  lower  extremity  of  the  trachea,  just  where  it  subdivides 
into  the  bronchial  tubes;  and  it  is  of  very  complex  construction,  espe- 
cially in  the  singing  birds.  In  Mammalia,  on  the  other  hand,  the 
vocal  organ  and  the  regulator  of  the  respiration  are  united  in  the 
larynx,  which  is  situated  at  the  top  of  the  trachea.  There  are  few,  if 
any,  of  this  class,  which  have  not  some  vocal  sound  ;  but  the  variety 
and  expressiveness  which  can  be  given  to  it,  differ  considerably  in  the 
several  orders ;  being  by  far  the  greatest  in  Man,  who  alone,  there  is 
reason  to  believe,  has  the  power  of  producing  articulate  sounds,  or 
proper  language. 

974.  The  Larynx  is  built  up,  as  it  were,  upon  the  Cricoid  cartilage 
(Fig.  153,  X  w  r  u),  which  surmounts  the  trachea,  and  which  might 
be  considered  as  its  highest  ring,  modified  in  form,  its  depth  from 
above  downwards  being  much  greater  posteriorly  than  anteriorly. 
This  is  embraced,  as  it  were,  by  the  Thyroid  cartilage  (g  e  h);  which 
is  articulated  to  the  sides  of  the  Cricoid  by  its  lower  horns,  round  the 
extremities  of  which  it  may  be  considered  to  rotate,  as  on  a  pivot.    In 


STRUCTURE  OF  THE  LARYNX. 


553 


this  manner,  the  front  of  the  Thyroid  cartilage  may  be  lifted  up,  or  de- 
pressed, by  the  muscles  which  act  upon  it;  whilst  the  position  of  its 
posterior   part  is  but   little 

changed.     Upon  the  upper  Fig.  153. 

surface  of  the  back  of  the  ep 

Cricoid  cartilage,  are  seated  i 

the  two  small  Arytenoid  car- 
tilages (n  f)  ;  these  are  so 
tied  to  the  cricoid  by  a  bun- 
dle of  strong  ligaments  (b 
b),  as  to  have  a  sort  of  rota- 
tion upon  an  articulating 
surface,  which  enables  them 
to  be  approximated  or  sepa- 
rated from  each  other, — 
their  inner  edges  being 
nearly  parallel  in  the  first 
case,  but  slanting  away  from 
each  other  in  the  second. 
To  the  summit  of  these  car- 
tilages are  attached  the 
ChordcB  vocales,  or  vocal 
ligaments  (t  u)  composed  of 
yellow  fibrous  or  elastic  tis- 
sue. These  stretch  across 
to  the  front  of  the  Thyroid 
cartilage;  and  it  is  upon  their 
condition  and  relative  situation,  that  the  absence  or  the  production  of 
vocal  tones,  and  all  their  modifications  of  pitch,  depend.  They  are 
rendered  tense  by  the  depression  of  the  front  of  the  Thyroid  carti- 
lage, and  relaxed  by  its  elevation  ;  by  which  action  the  pitch  of  the 
tones  is  regulated.  But  for  the  production  of  any  vocal  tones  what- 
ever, they  must  be  brought  into  a  nearly  parallel  condition,  by  the 
mutual  approximation  of  the  points  of  the  arytenoid  cartilages  to 
which  they  are  attached  ;  whilst  in  the  intervals  of  vocalization,  these 
are  separated,  and  the  rima  glottidis,  or  fissure  between  the  chordae 
vocales,  assumes  the  form  of  a  narrow  V,  with  its  point  directed 
backwards. 

975.  Thus  there  are  two  sets  of  movements  concerned  in  the  act  of 
vocalization  : — the  regulation  of  the  relative  position  of  the  Vocal 
Cords,  which  is  effected  by  the  movements  of  the  Arytenoid  carti- 
lages;— and  the  regulation  of  their  tension,  which  is  determined  by 
the  movements  of  the  Thyroid  cartilage.  The  Arytenoid  cartilages  are 
made  to  diverge  from  one  another  by  means  of  the  Crico-arytenoidei 
postici  of  the  two  sides,  (n  /,  n  /,)  which  proceed  from  their  outer  cor- 
ners and  turn  somewhat  round  the  edge  of  the  Cricoid,  to  be  attached 
to  the  lower  part  of  its  back ;  their  action  is  to  draw  the  outer  corners 
of  the  Arytenoid  cartilages  outwards  and  downwards,  so  that  the 


Bird's-eye  view  of  larynx  from  above,  after  Willis: 
— G  E  H,  the  thyroid  cartilage,  embracing  the  ring  of 
the  cricoid  rw  x  w,  and  turning  upon  the  axis  xz, 
which  passes  through  the  lower  horns ;  n  f,  n  f,  the 
arytenoid  cartilages,  connected  by  the  arytenoideus 
transversus ;  T  v,  T  v,  the  vocal  ligaments ;  N  x,  the 
right  crico- arytenoideus  lateralis  (the  left  being  re- 
moved) ;  V  kf,  the  left  thyro-arytenoideus  (the  right 
being  removed) ;  N  Z,  N  Z,  the  crico-arytenoidei  pos- 
tici ;  B  B,  the  crico-arytenoid  ligaments. 


554     REGULATION  OF  THE  APERTURE  OF  THE  GLOTTIS. 

points  to  which  the  vocal  ligaments  are  attached  are  separated  from 
one  another,  and  the  rima  glottidis  is  thrown  open.  The  action  of 
these  muscles  is  antagonized  by  that  of  the  Arytenoideus  transversus^ 
which  draws  together  the  Arytenoid  cartilages  ;  and  by  that  of  the 
Crico-arytenoidei  laterales  of  the  two  sides,  (n  x,)  which  run  forwards 
and  downwards  from  the  outer  corners  of  the  Arytenoid  cartilages, 
and  tend  by  their  contraction  to  bring  together  their  anterior  points, 
to  which  the  Vocal  ligaments  are  attached. — The  depression  of  the 
front  of  the  Thyroid  cartilage,  and  the  consequent  tension  of  the  Vocal 
ligaments,  is  occasioned  by  the  conjoint  action  of  the  Crico-thyroidei 
of  the  two  sides,  which  occasions  the  Thyroid  and  Cricoid  cartilages 
to  rotate,  the  one  upon  the  other,  at  the  articulation  formed  by  the 
inferior  cornua  of  the  former ;  and  this  action  will  be  assisted  by  the 
SternO'thyroideiy  which  tend  to  depress  the  front  of  the  Thyroid  car- 
tilage, by  pulling  from  a  fixed  point  below.  On  the  other  hand,  the 
elevation  of  the  front  of  the  Thyroid  cartilage,  and  the  relaxation  of 
the  Vocal  ligaments,  are  effected  by  the  contraction  of  the  Thyro- 
arytenoidei  of  the  two  sides  (v  kf),  whose  attachments  are  the  same 
as  those  of  the  Vocal  ligaments  themselves  ;  and  this  is  aided  by  the 
Thyro-hyoidei,  which  will  tend  to  draw  up  the  front  of  the  Thyroid 
cartilage,  acting  from  a  fixed  point  above. 

976.  The  muscles  which  govern  the  aperture  of  the  glottis, — those 
namely,  which  separate  and  bring  together  the  arytenoid  cartilages, 
and  thus  widen  or  contract  the  space  between  the  posterior  extremi- 
ties of  the  vocal  ligaments, — have  important  functions  in  connection 
with  the  Respiratory  actions  in  general,  and  stand  as  guards,  so  to 
speak,  at  the  entrance  to  the  lungs.  We  can  entirely  close  the 
glottis,  through  their  means,  by  an  effort  of  the  Will,  either  during 
inspiration  or  expiration  ;  and  it  is  a  spasmodic  movement  of  this  sort, 
which  is  concerned  in  the  acts  of  Coughing  and  Sneezing,  the  purpose 
of  which  is  to  expel,  by  a  sudden  and  powerful  blast  of  air,  any  irri- 
tating substances,  whether  solid,  liquid,  or  gaseous,  which  have  found 
their  way  into  the  air-passages.  These  muscles  appear  to  be  under 
the  sole  direction  of  the  inferior  or  recurrent  laryngeal  nerve  ;  which 
seems  to  possess  exclusively  motor  endowments.  When  this  nerve 
is  divided,  on  each  side,  or  when  the  par  vagum  is  divided  above  its 
origin,  the  muscles  of  the  larynx  (with  the  exception  of  the  crico- 
thyroid) are  paralyzed  ;  and  the  aperture  of  the  glottis  may  remain 
open,  or  may  be  entirely  closed,  according  to  the  manner  in  which  its 
lips  are  aff*ected  by  the  currents  of  air  in  egress  or  ingress.  It  is 
found  that,  under  such  circumstances,  tranquil  respiration  may  be 
carried  on  ;  but  that  any  violent  ingress  or  egress  of  air  will  tend  to 
drive  the  lips  of  the  glottis  (these  being  in  a  state  of  complete  relaxa- 
tion) into  apposition  with  each  other,  so  as  completely  to  close  the 
aperture.  The  character  of  the  superior  laryngeal  nerve  appears  to 
be  almost  exclusively  afferent ;  no  muscle,  except  the  crico-thyroid, 
being  thrown  into  contraction  when  it  is  irritated ;  whilst,  on  the 
other  hand,  if  it  be  divided,  neither  the  act  of  coughing,  nor  any 


PRODUCTION  OF  VOCAL  SOUNDS.  555 

reflex  respiratory  movement  whatever,  can  be  excited,  by  irritating 
the  lining  membrane  of  the  larynx. 

977.  Daring  the  ordinary  acts  of  inspiration  and  expiration,  the 
Chordae  vocales  appear  to  be  widely  separated  from  each  other,  and 
to  be  in  a  state  of  the  freest  possible  relaxation.  In  order  to  produce 
a  vocal  sound,  they  must  be  made  to  approach  one  another,  and  their 
inner  faces  must  be  brought  into  parallelism  ;  both  of  which  ends  are 
accomplished  by  the  rotation  of  the  Arytenoid  cartilages ;  whilst,  at 
the  same  time,  they  must  be  put  into  a  certain  degree  of  tension,  by 
the  depression  of  the  Thyroid  cartilage.  Both  of  these  movements 
take  place  consentaneously,  and  are  mutually  adapted  to  each  other ; 
the  vocal  ligaments  being  approximated,  and  the  rima  glottidis  con- 
sequently narrowed,  at  the  same  time  that  their  tension  is  increased. 
There  is  a  certain  aperture,  which  is  favourable  to  the  production  of 
each  tone,  although  the  pitch  itself  is  governed  by  the  tension  of  the 
Vocal  Cords ;  and  it  is,  perhaps,  to  a  want  of  consent  between  the 
two,  that  the  peculiarly  discordant  nature  of  some  voices,  which  appear 
incapable  of  producing  a  distinct  musical  tone,  is  due. 

978.  It  has  been  fully  proved,  by  the  researches  of  Willis,  Miiller, 
and  others,  that  the  action  of  the  Vocal  ligaments,  in  the  production  of 
sound,  bears  no  resemblance  to  that  of  vibrating  strings ;  and  that  it 
is  not  comparable  to  that  of  the  mouth-piece  of  the  flute-pipes  of  the 
Organ :  but  that  it  is,  in  all  essential  particulars,  the  same  with  that 
of  the  reeds  of  the  Hautboy  or  Clarionet,  or  the  tongues  of  the  Accor- 
dion or  Concertina.  All  the  phenomena  attending  the  production  of 
Musical  tones  are  fully  explicable  on  this  hypothesis;  except  the  pro- 
duction oi  falsetto  notes,  which  has  not  yet  been  clearly  accounted 
for. — The  power  which  the  Will  possesses,  of  determining,  with  the 
most  perfect  precision,  the  exact  degree  of  tension  w-hich  these  liga- 
ments shall  receive,  is  extremely  remarkable.  Their  average  length 
in  the  Male,  in  the  state  of  repose,  is  estimated  by  Miiller  at  about 
73-lOOths  of  an  inch;  whilst,  in  the  state  of  greatest  tension,  it  is 
about  93-lOOths;  the  whole  difference,  therefore,  is  not  above  20- 
lOOths,  or  one-fifth  of  an  inch.  In  the  female  glottis,  their  average 
dimensions  are  about  51-lOOths  and  63-lOOths,  respectively  ;  so  that 
the  difference  is  here  only  12-lOOths,  or  less  than  one-eighth  of  an 
inch.  Now  the  natural  compass  of  the  voice,  in  most  persons  who 
have  cultivated  the  vocal  organ,  may  be  stated  at  about  two  octaves, 
or  24  semitones.  Within  each  semitone,  a  singer  of  ordinary  capa- 
bility could  produce  at  least  ten  distinct  intervals  ;  so  that  for  the  total 
number  of  intervals,  240  is  a  very  moderate  estimate.  There  must, 
therefore,  be  at  least  240  diflferent  states  of  tension  of  the  vocal  cords, 
every  one  of  which  can  be  at  once  determined  by  the  will,  when  a  dis- 
tinct conception  exists  of  the  tone  to  be  produced  (§  904);  and,  as  the 
whole  variation  in  their  length  is  not  more  than  one-fifth  of  an  inch, 
even  in  Man,  the  variation  required,  to  pass  from  one  interval  to  an- 
other, will  not  be  more  than  l-1200lh  of  an  inch. — And  yet  this  esti- 
mate is  much  below  that,  which  might  be  truly  made  from  the  per- 


556  REGULATION  OF  THE  PITCH  OF  VOCAL  SOUNDS. 

formance  of  a  practiced  vocalist.  The  celebrated  Madame  Mara  is 
said  to  have  been  able  to  sound  50  different  intervals  between  each 
semitone  ;  the  compass  of  her  voice  was  at  least  40  semitones,  so  that 
the  total  number  of  intervals  w^as  2000.  The  extreme  variation  in 
the  length  of  the  vocal  cords,  even  taking  the  larger  scale  of  the  Male 
larynx,  not  being  more  than  the  fifth  of  an  inch,  it  may  be  said  that 
she  w^as  able  to  determine  the  contractions  of  her  vocal  muscles  to 
the  ten-thousandth  of  an  inch. 

979.  It  is  on  account  of  the  greater  length  of  the  Vocal  cords,  that 
the  pitch  of  the  voice  is  much  lower  in  Man  than  in  Woman  :  but  this 
difference  does  not  arise  until  the  end  of  the  period  of  childhood, — 
the  size  of  the  larynx  being  about  the  same  in  the  Boy  and  Girl,  up  to 
the  age  of  14  or  15  years,  but  then  undergoing  a  rapid  increase  in 
the  former,  whilst  it  remains  nearly  stationary  in  the  latter.  Hence  it 
is  that  Boys,  as  well  as  Girls  and  Women,  sing  treble;  whilst  Men 
sing  tenor  J  which  is  about  an  octave  lower  than  the  treble  ;  or  hass^ 
which  is  several  notes  lower  still. — The  cause  of  the  variations  in  the 
timbre  or  quality  in  different  voices,  is  not  certainly  known  ;  but  it 
appears  to  be  due,  in  part,  to  differences  in  the  degree  of  flexibility 
and  smoothness  in  the  cartilages  of  the  larynx.  In  women  and 
children,  these  cartilages  are  usually  soft  and  flexible,  and  the  voice 
is  clear  and  smooth  ;  whilst  in  men,  and  in  women  whose  voices  have 
a  masculine  roughness,  the  cartilages  are  harder,  and  are  sometimes 
almost  completely  ossified.  The  loudness  of  the  voice  depends  in 
part  upon  the  force  with  which  the  air  is  expelled  from  the  lungs  ; 
but  the  variations  in  this  respect,  which  exist  among  different  indi- 
viduals, seem  partly  due  to  the  degree  in  which  its  resonance  is 
increased  by  the  vibration  of  the  other  parts  of  the  larynx,  and  of  the 
neighbouring  cavities.  In  the  Howling  Monkeys  of  America,  there 
are  several  pouches  opening  from  the  larynx,  which  seem  destined  to 
increase  the  volume  of  tone  that  issues  from  it;  one  of  these  is  exca- 
vated in  the  substance  of  the  hyoid  bone  itself.  Although  these 
Monkeys  are  of  inconsiderable  size,  yet  their  voices  are  louder  than 
the  roaring  of  lions,  and  are  distinctly  audible  at  the  distance  of  two 
miles;  and  when  a  number  of  them  are  congregated  together,  the 
effect  is  terrific. 

980.  The  vocal  sounds  produced  by  the  action  of  the  larynx  are 
of  very  different  characters  ;  and  may  be  distinguished  into  the  cry, 
the  song,  and  the  ordinary  or  acquired  voice.  The  cry  is  generally  a 
sharp  sound,  having  little  modulation  or  accuracy  of  pitch,  and  being 
usually  disagreeable  in  its  timbre  or  quality.  It  is  that  by  which  ani- 
mals express  their  unpleasing  emotions,  especially  pain  or  terror;  and 
the  Human  infant,  like  many  of  the  lower  animals,  can  utter  no  other 
sound. — In  song,  by  the  regulation  of  the  vocal  cords,  definite  and 
sustained  musical  tones  are  produced,  which  can  be  changed  or  mo- 
dulated at  the  will  of  the  individual.  Different  species  of  Birds  have 
their  respective  songs ;  which  are  partly  instinctive,  and  partly  ac- 
quired by  education.    In  Man,  the  power  of  song  is  entirely  acquired  j 


VARIOUS  KINDS  OF  VOCAL  SOUNDS.  557 

but  some  individuals  possess  a  much  greater  facility  in  acquiring  it 
than  others, — this  superiority  appearing  to  depend  upon  their  more 
precise  conception  of  the  tones  to  be  sounded,  as  well  as  their  more 
ready  imitation, — besides  differences  in  the  construction  of  the  larynx 
itself.  The  larynx  of  an  accomplished  vocalist,  obedient  to  the  ex- 
pression of  the  emotions,  as  well  as  to  the  dictates  of  the  will,  may 
be  said  to  be  the  most  perfect  musical  instrument  ever  constructed. — 
The  voice  is  a  sound  more  resembling  the  cry,  in  regard  to  the  absence 
of  any  sustained  musical  tone  ;  but  it  differs  from  the  cry,  both  in  the 
quality  of  its  tone,  and  in  the  modulation  of  which  it  is  capable  by 
the  will.  In  ordinary  conversation,  the  voice  passes  through  a  great 
variety  of  musical  tones,  in  the  course  of  a  single  sentence,  or  even 
a  single  word, — sliding  imperceptibly  from  one  to  another ;  and  it  is 
when  we  attempt  to  fix  it  definitely  to  a  certain  pitch,  that  we  change 
it  from  the  spea/dng  to  the  singing  tone. 

981.  The  power  of  producing  articulate  sounds,  from  the  combina- 
tion of  which  Speech  results,  is  altogether  independent  of  the  Larynx ; 
being  due  to  the  action  of  the  muscles  of  the  mouth,  tongue,  and  pa- 
late. Distinctly  articulate  sounds  may  be  produced  without  any  vocal 
or  laryngeal  tone,  as  when  we  whisper ;  and  it  has  been  experiment- 
ally shown,  that  the  only  condition  necessary  for  this  mode  of  speech, 
is  the  propulsion  of  a  current  of  air  through  the  mouth,  from  back  to 
front.  On  the  other  hand,  we  may  have  the  most  perfect  laryngeal 
tone  without  any  articulation  ;  as  in  the  production  of  musical  sounds, 
not  connected  with  words.  But  in  ordinary  speech,  the  laryngeal 
tone  is  modified  by  the  various  organs,  which  intervene  between  the 
larynx  and  the  os  externum.  The  simplest  of  these  modifications  is 
that  by  which  the  Vowel  sounds  are  produced  :  these  sounds  being 
continuous  tones  modified  by  the  form  of  the  aperture  through  w^hich 
they  pass  out.  Thus,  let  the  reader  open  his  mouth  to  the  widest 
dimensions,  depress  the  tongue,  and  raise  the  velum  palati,  so  as  to 
make  the  exit  of  air  as  free  as  possible  ;  on  then  making  a  vocal 
sound,  he  will  find  that  this  has  the  character  of  the  vowel  a  in  ah. 
On  the  other  hand,  if  he  draw  together  the  lips,  still  keeping  the 
tongue  depressed,  he  will  pass  to  the  sound  represented  in  the  Eng- 
lish language  by  oo,  in  the  Continental  languages  by  u.  By  atten- 
tion to  the  production  of  other  vowel  sounds,  it  will  be  found  that 
they  are  capable  of  being  formed  by  similar  modifications  in  the  form 
of  the  buccal  cavity  and  the  size  of  the  buccal  orifice;  and  that  they 
are  capable  of  being  sustained  for  any  length  of  time.  There  is  an 
exception,  however,  in  regard  to  the  sound  of  the  English  i,  as  in 
fine;  which  is,  in  reality,  a  diphthongal  sound,  produced  in  the  act 
of  transition  from  a  peculiar  indefinite  murmur  to  the  sound  of  the 
long  e,  which  takes  its  place  when  w^e  attempt  to  continue  it.  The 
short  vowel  sounds,  moreover, — such  as  a  in  Jat,  e  in  met,  o  in  pot, 
&c.,  are  not  capable  of  being  perfectly  prolonged  ;  as  they  require, 
for  their  true  enunciation,  to  be  immediately  followed  by  a  consonant. 
— A  tolerably  good  artificial  imitation  of  Vowel  sounds  has  been 


558  VOWELS  AND  CONSONANTS.— STAMMERING. 

effected,  by  means  of  a  reed-pipe  representing  the  larynx,  surmounted 
by  an  India-rubber  ball,  with  an  orifice,  representing  the  cavity  and 
orifice  of  the  mouth.  By  modifying  the  form  of  the  ball,  the  different 
vowels  could  be  sounded  during  the  action  of  the  reed. 

982.  In  the  production  of  the  sounds  termed  Consonants,  the  breath 
suffers  a  more  or  less  complete  interruption,  in  its  passage  through 
the  parts  anterior  to  the  larynx.  The  most  natural  primary  division 
of  these  sounds  is  into  those  which  require  a  total  stoppage  of  the 
breath  at  the  moment  previous  to  their  being  pronounced,  and  which, 
therefore,  cannot  be  prolonged  ;  and  those  in  pronouncing  which  the 
interruption  is  partial,  and  which  can,  like  the  vowel  sounds,  be  pro- 
longed ad  libitum.  The  former  have  received  the  designation  of 
explosive  consonants  ;  the  latter  are  termed  continuous. — In  pronoun- 
cing any  consonants  of  the  explosive  class,  the  posterior  nares  are  com- 
pletely closed  ;  and  the  whole  current  of  air  is  directed  through  the 
mouth.  This  may  be  checked  by  the  approximation  of  the  lips,  as 
in  pronouncing  b  andp;  by  the  approximation  of  the  point  of  the 
tongue  to  the  front  of  the  palate,  as  in  pronouncing  d  and  t ;  or  by 
the  approximation  of  the  middle  of  the  tongue  to  the  arch  of  the 
palate,  as  in  pronouncing  the  hard  g  or  k.  The  difference  between 
6,  d,  and  g,  on  the  one  hand,  and  p,  t,  and  k,  on  the  other,  depends 
simply  upon  the  greater  extent  of  the  meeting  surfaces  in  the  former 
case  than  in  the  latter. — In  sounding  some  of  the  continuous  conso- 
nants, the  air  is  not  allowed  to  pass  through  the  nose  ;  but  the  inter- 
ruption in  the  mouth  is  incomplete  ;  this  is  the  case  with  v  andjT,  s 
and  z.  In  others,  the  posterior  nares  are  not  closed,  and  the  air  has 
a  nearly  free  passage,  either  through  the  nose  alone,  as  in  m  and  w, 
or  through  the  nose  and  mouth  conjointly  as  in  /  and  r.  The  sound 
of  k  is  a  mere  aspiration,  caused  by  an  increased  force  of  breath; 
and  that  of  the  guttural  ch,  as  it  exists  in  Welsh,  Gaelic,  and  most 
Continental  languages,  is  an  aspiration  modified  by  the  elevation  of 
the  tongue,  which  causes  a  slight  obstruction  to  the  air,  and  an  in- 
creased resonance  in  the  back  of  the  mouth. 

983.  The  study  of  the  mode  in  which  the  different  Consonants  are 
produced,  is  of  particular  importance  to  those  who  labour  under 
defective  speech,  especially  that  difficulty  which  is  known  as  Slam- 
mering.  This  very  annoying  impediment  is  occasioned  by  a  want 
of  proper  control  over  the  muscles  concerned  in  Articulation  ;  which, 
instead  of  obeying  the  Will,  are  sometimes  affected  with  an  involun- 
tary or  spasmodic  action,  that  interrupts  the  pronunciation  of  particular 
words, — ^just  as,  in  Chorea,  the  muscles  of  the  limbs  are  interrupted 
by  spasmodic  twitchings,  in  the  performance  of  any  voluntary  move- 
ment. In  fact,  persons  affected  with  general  Chorea,  frequently 
stammer ;  showing  that  ordinary  Stammering  may  be  considered  as  a 
kind  of  local  Chorea.  The  analogy  between  the  two  states  is  further 
indicated  by  the  corresponding  influence  of  excited  Emotions  in 
aggravating  both. — It  is  in  the  pronunciation  of  the  consonants  of 
the  explosive  class,  that  the  stammerer  usually  experiences  the  greatest 


STAMMERING.  559 

difficulty;  forthe  total  interruption  to  the  breath,  which  they  occasion, 
is  frequently  continued  involuntarily;*  so  that  either  the  expiration  is 
entirely  checked,  the  whole  frame  being  frequently  thrown  into  the 
most  distressing  serai-convulsive  movements,  or  the  sound  comes  out 
in  jerks.  Sometimes,  however,  the  spasmodic  action  occurs  in  the 
pronunciation  of  vowels  and  continuous  consonants;  the  stammerer 
prolonging  his  expiration,  without  being  able  to  check  it. 

984.  The  best  method  of  curing  this  defect  (where  there  is  no  mal- 
formation of  the  organs  of  speech,  but  merely  a  want  of  power  to  use 
them  aright),  is  to  study  the  particular  difficulty  under  which  the 
individual  labours ;  and  then  to  cause  him  to  practise  systematically 
the  various  movements  concerned  in  the  production  of  the  sounds  in 
question,  at  first  separately,  and  afterwards  in  combination, — until 
he  feels  that  his  voluntary  control  over  the  muscles  is  complete.  The 
patient  would  at  first  do  well  to  practise  sentences,  from  which  the 
explosive  consonants  are  omitted  ;  his  chief  difficulty,  arising  from 
the  spasmodic  suspension  of  the  expiratory  movement,  being  thus 
avoided.  Having  mastered  these,  he  may  pass  on  to  others,  in  which 
the  difficult  letters  are  sparingly  introduced  ;  and  may  finally  accustom 
himself  to  the  use  of  ordinary  language.  One  of  the  chief  points 
to  be  aimed  at,  is  to  make  the  patient  feel  that  he  has  command 
over  his  muscles  of  articulation ;  and  this  is  best  done,  by  gradually 
leading  him  from  that  which  he  can  do,  to  that  which  he  fears  to 
attempt. 

•  The  interruption  of  the  expiratory  movement  in  Stammering,  is  usually  stated 
to  take  place  in  the  glo/tis ,-  but  the  Author  is  satisfied  that,  in  all  ordinary  cases  at 
least,  it  is  in  that  condition  of  the  mouth  which  is  preparatory  to  the  pronunciation 
of  one  of  the  explosive  consonants. 


INDEX. 


N.  B.  The  Numbers  refer  to  the  Paragraphs. 


Aberration,  corrected  in  eye,  957. 
Absorbent  Cells,  241-244. 

«         Vessels,  489. 
Absorption,  from  alimentary  canal,  489, 490; 
by  lacteals,  241-244;  by  blood- 
vessels, 491-493. 
**  from   general    and    pulmonary 

surfaces,  522,  523. 
**  interstitial,  by  lymphatics,  502, 

503;   by   blood-vessels,   502, 
503. 
Acalepha,  circulation  in,  550. 
Adipose  tissue,  259-263,  423-425. 
Air-cells  of  lungs,  676-679. 
Albumen,  173-175. 

"         conversion  of  into  fibrin,  519. 
Albuminuria,  533,  728. 
Aliment,  sources  of  demand  for,  406-415. 
"         effect   of  variations  in   supply  of, 

416-426. 
<*         relative  value  of  different  kinds  of, 

427,  441. 
"         necessity  for  mixture  in,  437. 
Allantois,  formation  of,  817. 
Amnion,  formation  of,  816. 
Amphioxus,  see  Lancelot. 
Anterior  Pyramids,  890. 
Apoplexy,  688,  922. 
Area  pellucida,  808. 
Areolar  tissue,  194-196,  205. 
Arteries,  movement  of  Blood  in,  582-588. 
"         elasticity  of,  583;  tonicity  of,  584; 
contractility  of,  585;  pulsation  of, 
583,  584. 
"        anastomosis  of,  588. 
Articulata,  circulation  in,  552,  553;  respi- 
ration in,  657-660;  nervous  system  in,  657 
-660. 
Articulate  speech,  981,  982. 
Asphyxia,  628,  703-709. 
Assimilating  cells,  212,  514,  519. 
Assimilation,  519. 
Asthma,  678. 
Atrophy,  619,  620. 
Attention,  effects  of,  935. 
Auditory  ganglia,  900. 
"        nerve,  949. 

36 


Azotized  Compounds  in  Plants,  169, 428, 429. 
«  "  in  Animals,  428,  429. 

*'  "  destination  of  in   food, 

429,  431,  433. 


B 


Basement  membrane,  206-209. 

Batrachia,  respiration  of,  670,  671. 

Bile,  composition  and  properties  of,  724-726. 

"     uses  of,  in  digestion,  476-479. 
Birds,  circulation   in,  564,  565;  respiration 

in,   672-674;    lymphatic   system   in,   500; 

nervous  centres  of,  872;  heat  of,  761. 
Blood,  composition  of,  525-529;  uses  of  seve- 
ral constituents  of,  529, 530;  changes 
of,  in  disease,  531-534. 

"     corpuscles  of,  white,  212;  red,  215- 
223. 

"     coagulation  of,  535. 

«     buffy  coat  of,  536,  537. 

**     rate  of  movement  of,  577. 

**     influence  of  respiration  on,  609-702. 
Blushing,  603. 

Bone,  structure  and  composition  of,  277-289. 
Brunner's  glands,  450. 
Buffy  coat  of  blood,  536,  537. 
Butyric  acid,  430. 


Cancelli  of  Bone,  281. 
Cancer-cells,  248. 

Capillaries,  movement  of  Blood  in,  589-604; 
variations  in  its  rate,  597. 
"  variations  in  size  of,  595,  603; 

influence  of  nerves  upon,  603, 
604. 
**  independent  force  generated  in, 

598-600. 
Carbonic  acid,  necessity  for  excretion  of,  641; 
sources  of,    in  Animal   bo- 
dies, 642-648. 
"         "      mode  of  its  extrication,  649- 
652;  amount  set  free,  691- 
698. 
Cartilage,  264-273. 


562 


INDEX. 


Cartilage,  ossification  of,  300-303. 
Casein,  176,  832. 
Catamenia,  798,  799. 

Cell^  Vegetable,  general  history  of,  30-45. 
*'     Animal,  general  history  of,  211-214. 
"     isolated,  various  forms  of,  210-216. 
**     the  immediate  agents  in  Organic  func- 
tions, 245,  246. 
"     union  of,  247-254. 
"     coalescence  of,  255-257. 
"     changes  of  form  in,  258. 
Cellular  cartilage,  267,  268. 
Cementum,  319. 

Centipede,  experiments  on,  858. 
Cerebellum,  867,  869. 

"  functions  of,  911-914. 

Cerebric  acid,  383. 
Cerebrum,  867,  868. 

«  functions  of,  915-925. 

Chlorosis,  state  of  blood  in,  219,  533,  537. 
Cholesterine,  724. 
Chondrine,  264,  265. 
Chorda  dorsalis,  254,  812. 
Chordaj  vocales,  974-979. 
Chorea,  983. 
Chorion,  795,  809,  818. 

Chyle f  composition  and  properties  of,  515- 
519. 
«       corpuscles  of,  212,  518,  519. 
Chyme,  472,  476. 
Cicatricula,  808. 
Cilia,  234,  235. 
Cineritious  substance,  379. 
Circulation,  538,539;  iji  Plants,  540-548; 
in  lowest  Animals,  549,  550 ; 
in  Echinodermata,  552;    in 
Articulata,  552, 553;  in  Mol- 
lusca,  555-557;    in  Fishes, 
558-561;   in  Reptiles,  562, 
563;  in  Birds  and  Mammals, 
564,  565. 
"  in  early  embryo,  551 ,  554,  566; 

in  foetus  at  birth,  823,  824. 
Coagulation  of  Albumen,  173,  174. 
"  of  Blood,  535. 

"  of  Casein,  176. 

«  of  Fibrin,  180-187. 

Cochlea,  952. 

Csecum,  secondary  digestion  in,  4S1. 
Cold,  degree  of,  sustainable  by  Plants,  110, 
111. 
"     degree  of,  sustainable  by  Animals,  136. 
Colostrum,  835. 
Colours,  perception  of,  971, 
Commissures  of  brain,  917-919. 
Complementary  colours,  972. 
Conchifera,  nervous  system  of,  852,  853. 
Concussion,  581. 
Congestion,  601,  602. 

'<  venous,  609,  610.  • 

Consensual  actions,  903-905. 
Consonants,  982. 
Contractility  of  Muscle,  347. 

«  Vegetable  tissues,  345,  346. 

Convulsive  actions,  885. 
Cornea,  274. 
Corpora  Malpighiana,  728. 

<«       Quadrigemina,  873,  900,  902. 
*'       Striata,  901. 


Corpora  Wolffiana,  727. 
Corpuscles  of  Blood;  red,  215-223;  white, 
212. 
"  of  Chyle  and  Lymph,  212. 

Cortical  substance  of  brain,  380. 
Cranium,  circulation  in,  611. 
Crura  cerebri,  901. 
Crustacea,  geographical  distribution  of,  130; 

respiration  of,  658. 
Crusta  petrosa,  319. 
Crystaline  lens,  275. 
Cuttle-fish,  nervous  cords  in  arras  of,  854. 


Daltonism,  971. 

Death,  somatic,  65,  68,  69,  628,  629. 
"       molecular,  QQ,  67. 

Decidua,  810,  811. 

Defecation,  462,  463. 

Deglutition,  453,  454,  897. 

Dentine,  311-316. 

Determination  of  blood,  601. 

Development  of  Embryo,  805  et  seq. 

Diffusion,  mutual,  of  gases,  650. 

Digestion,  organs  of,  442-450. 

"  nature  of  the  process,  472. 

Disintegration  of  tissues,  617. 

*'  of  Muscular  tissue,  361. 

"  of  Nervous  tissue,  384. 

Distances,  estimate  of,  966,  967. 

Doris,  gills  of,  651,  656. 

Double  vision,  963. 

Draper,  Prof.,  his  views  on  the  capillary  cir- 
culation, 545-548,  598,  599. 

Dreaming,  923. 

Duration  of  pregnancy,  825,  826. 
"         of  impressions  on  Ear,  956. 
"         of  impressions  on  Eye,  970. 

Dytiscus,  experiments  on,  859. 


Ear,  structure  of,  956-960. 
Echinodermata,  circulation  in,  552. 
Electricity,  development  of  in  Animals,  771- 
777;  in  Torpedo  and  Gymno- 
tus,  771-775;  in  Muscles,  775; 
in  Frog,  776;    in  higher  ani- 
mals, 777. 
"  influence   of,   on   organic    func- 

tions,   142,    146;     efi'ects    of 
shocks  of,  145-147. 
*<  influence  of,  on  Muscles,  351 

on  sensory  nerves,  932. 
Embryo,   early   development   of,   805 — 808 
formation  of  vertebral  column  in 
812;  formation  of  vessels  in,  813 
formation  of  heart  in,  814;  forma 
tion  of  digestive  cavity  in,  815 
circulation  in,  551,  554,  556. 
Emotional  movements,  906-908. 
Emotions,  influence  of  on  hunger,  483;  on 
salivary  secretion,  467;  on  heart's  action, 
580;  oncapillary  circulation,  603;  on  mam- 
mary secretion,  836,  837. 
Enamel,  317,  318. 


INDEX. 


563 


Endosmose,  491,  492. 
Entozoa,  circulation  in,  549,  550. 
Epidermis,  224-228. 
Epilepsy,  886. 
Epithelium,  231-239. 
Erect  vision,  963. 

Exhalation  of  water,  from  lungs,  701;  from 
cutaneous  surface,  743-746. 
"  of  organic  matter,  702. 

Excreting  processes,  general  review  of,  757- 

759. 
Eye,  structure  of,  956-960. 


Facial  nerve,  888. 
Fat,  259-263,  423-425. 
Fecundation  of  Ovum,  803,  804. 
Ferments,  action  of,  on  blood,  534. 
Fertilization  of  ovum,  803,  804. 
Fibre,  white,  189,  190. 

«      yellow,  189,  192. 
Fibrillation,  183,  213. 
Fibrin,  coagulation  of,  180-187. 

«       composition  of,  178,  179. 

*^       production  of,  519. 
Fibrous  membranes,  188. 
Fibrous  tissues,  simple,  188-193. 
Fibro-Cartilage,  188,  269,  272. 
Fifth  Pair,  686,  888. 
Fishes,  lymphatic  system  in,  499;  circulation 

in,  558-561;  respiration  in,  663-667;  heat 

of,  761;    electricity  of,  771-774;  nervous 

centres  in,  869,  870. 
Fostus,  circulation  in,  822-824. 
Follicles  of  glands,  238,  714-719. 
Follicles  of  Lieberkiihn,  449. 
Food,  see  Aliment. 


Gall-bladder,  481. 

Ganglion,  380. 

Gangrene,  633,  634. 

Gases,  mutual  diffusion  of,  650. 

Gastric  fluid,  properties  and  actions  of,  468- 

472. 
<«        *«      conditionsof  its  secretion,  474, 

475. 
Gastric  follicles,  470. 
Gelatin,  190,  191,  429. 
Geographical  distribution  of  Animals,  130. 

*'  distribution  of  Plants,  102-106. 

Germinal  membrane,  806. 
Gestation,  duration  of,  825,  826. 
Gills," structure  of,  651,  655,  656,  663. 
Glands,  essential  parts  of,  238,  714-719. 
Globuline,  221. 

Glosso-pharyngeal  nerve,  888,  897, 
Glottis,  regulation  of  aperture  of,  976. 
Glycerine,  261. 
Gout,  422,  615. 
Graafian  Vesicle,  796. 
Granulation,  636. 
Gravity,  influence  of  on  venous  circulation, 

609,  610. 
Gray  matter  of  nerves,  379. 
Gymnotus,  771,  774. 


H 


Haematine,  221,  222. 
Hair,  328-330. 
Haversian  canals,  282. 
Hearing,  sense  of,  949-954. 
Heart,  action  of,  668-570;  sounds  of,  571- 
575;  propulsive  power  of,  576-578; 
frequency  of  contractions  of,  579. 
**        power   of,   independent   of   nervous 
agency,  580  ;  influenced  by  mental 
emotions,  580;  by  state  of  nervous 
system,  581. 
"        first  development  of,  in  embryo,  814. 
Heat,  amount  developed  in  Insects,  123;  in 
Fishes,  760;  in  Birds,  761;  in  Mam- 
mals, 761;  in  Plants,  762. 
**     development  of,  chiefly  dependent  on 
production  of  carbonic  acid,  764;  but 
partly  on  other  oxidizing  processes, 
765;  inferior  in  young  animals,  766. 
**     of  body,  kept  down  by  perspiration, 

745,  768. 
"     its  influence  upon  vital  activity  in  gene- 
ral, 97,  98;  upon  Vegetation,  99-111; 
upon  Animal  life,  112-141. 
"     degree  of,  sustainable  by  Animals,  138 
-141;  by  Plants,  108. 
Hippuric  acid,  734, 
Hunger,  sense  of,  483,  485. 
Hybernation,  120,  121. 
Hydra,  stomach  of,  443. 
Hydrophobia,  886,  908. 
Hypertrophy,  617,  618. 
Hypoglossal  nerve,  888. 
Hysteria,  741,  887,  908. 


Incubation,  heat  supplied  in,  125-127. 

Inflammation,  nature  of  the  process,  631, 632; 
state  of  the  blood  in,  531,  536. 

Inorganic  substances  in  food,  438-441. 

Insalivation,  446,  451,  452, 

Insects,  circulation  in,  552;  respiration  in, 
659,  660;  nervous  system  of,  856-864;  re- 
flex actions  of,  859,  860;  instinctive  actions 
of,  860,  861;  heat  of,  123, 

Instinctive  actions  of  Man,  906. 

Intelligence,  916. 

Intercellular  substance,  247,  253. 

Intestinal  canal,  structure  of,  447-450;  move- 
ments of,  460,  461. 

Iris,  movements  of,  969. 

Irritability  of  Muscles,  348-363. 


Kidneys,  structure  of,  727,  728 ;  action  of, 
729-741. 


Lacteal s,  481,  496,  499. 
Lactic  acid,  735. 
Lacuna  of  Bone,  279. 


564 


INDEX. 


Lancelot,  254,661,869. 
Laryngeal  nerves,  976. 
Larynx,  structure  and  actions  of,  974,  979. 
Lead-palsy,  614. 

Light,  laws  of  transmission  and  refraction  of, 
955. 

«'  influence  of  on  Vegetation,  79-92;  on 
growth  and  development  of  animals, 
93-96. 

"       emission  of,  by  animals,  770;  by  man, 
771. 
Lime,  in  Animal  body,  438,  440,  441. 
Lithic  acid  diathesis,  422,  732,  733. 
Liver,  structure  of,  720-723;  actions  of,  477- 

479,  724-726. 
Luminousness,  animal,  770,  771. 
Lungs,  structure  of,  676-679. 
Lymph,  composition  and  properties  of,  515, 

520. 
Lymphatics,  498-503. 


M 


Male,  action  of  in  reproduction,  785-790. 

Malignant  diseases,  640. 

Malpighian  bodies,  of  Kidney,  728;  of  Spleen, 

506. 
Mammalia,  lymphatic  system  in,  500;  circu- 
lation in,  564,  565;  respiration  in,  674,  675; 
heat  evolved  in,  761;  nervous  centres  of, 
873;  ovisac  of,  795. 
Mammary  glands,  830,  831. 
Margarine,  261. 

Mastication,  act  of,  451,  452,  896. 
Medulla   Oblongata,  structure   of,   889-893; 

functions  of,  894-899. 
Memory,  924. 

Menstrual  secretion,  798,  799. 
Mesenteric  glands,  496. 
Metamorphosis  of  animals,  407,  791,  792. 
Milk,  436;    composition  and  properties  of, 
832-834. 
"      circumstances  influencing  secretion  of, 
836,  839. 
Mineral  ingredients  of  food,  438-441. 
Moisture,  proportion  of,  in  different  parts  of 
the  body,  149-152;  influence  of,  on  growth 
of  Plants  and  Animals,  153-157;  effects  of 
withdrawal  of,  158-161. 
MoLLUSCA,  circulating   system  of,  555-557; 
respiratory  organs   of,  654-656;    nervous 
system  of,  850-855. 
Mucous  membrane,  198-204. 
Mucus,  237,  464. 

Muscles,  contractility  of,  345-371;  irritability 
of,  348-363;  tonicity  of,  364-366; 
rigor  mortis  of,  367-369;  peculiar 
force  of,  370;  heat  evolved  by, 
371;  electricity  evolved  by,  775. 
"         energy  of,  dependent  on  supply  of 

blood,  358-361. 
"         disintegration  of,  361. 
Muscular  fibre,  striated,  332,  334-339;  non- 
striated,  333,  337. 
Muscular  sense,  904.  ^ 

"         tissue,  340-344. 
Myopia,  958. 


N 


Nail,  226. 

Nervous  System,  general  view  of  actions  of, 

840-847. 
Nervous  System,  in  Radiata,  849;  in  Tunic- 
ata,  850,  851 ;  in  Bivalve  MoUusca,  852, 
853;  in  higher  Mollusca,  853,  854;  in  Ar- 
ticulata,  855-863;  in  Insects,  856,  857,  861; 
in  Vertebrata,  867,  868;  in  Fishes,  869, 
870;  in  Reptiles,  871;    in  Birds,  872;  in 
Mammals,  873. 
Nervous  tissue,  372-405;  fibrous,  373-377; 
vesicular,  378,  379. 
«'  "       activity   of,    dependent    on 

supply  of  arterial  blood, 
398-404. 
Nucleolus,  250. 
Nucleus,  249. 
Nutrition,  612-615. 

"  activity  of,  dependent  on  func- 

tional  activity  of  parts,  616- 
627. 


(Esophagus,  passage  of  food  along,  455,898. 
Oily  compounds  in  food,  430,  432,  435. 
Oleine,  261. 

Oleo-phosphoric  acid,  383. 
Olfactive  lobes,  869-873,  900. 
Olfactory  nerve,  946,  947. 
Olivary  bodies,  891. 
Optic  lobes,  869-873,  900. 
Optic  nerves,  910. 
Orbit,  motor  nerves  of  the,  888. 
Osseous  tissue,  277-289,  299-309. 
Ossification,  300-303. 
Otolithee,  950. 
Ova  of  animals,  791-794. 
Ovarium,  793-796. 
Ovisac,  793,  796. 

Oxygen,  necessity  for,  in  animal  body,  649 ; 
mode  of  introduction  of,  650-652. 


Pancreatic  secretion,  480. 

Papilla;,  sensory,  of  skin,  381, 940;  of  tongue, 

943. 
Parturition,  827-829. 
Par  Vagum,  459,  487, 580,  685,  686,  888, 895, 

897-899. 
Pedal  ganglia  in  Mollusca,  852,  853. 

"         «         in  Articulata,  857,  862. 
Pepsine,  470,  471. 
Perception,  nature  of,  936,  937. 
Perceptions,  tactual,  941;  visual,  961,  968. 
Peristaltic  movement,  460. 
Perspiration,  743-746. 
Peyer's  glands,  450. 
Phosphate  of  lime,  in  food,  438-441. 
Phosphatic  deposits,  386,  738-740. 
Phosphorus,  in  animal  body,  438,  439. 
Pigment-cells,  229,  230. 
Placenta,  structure  of,  819,  820. 
Placental  tufts,  244. 


INDEX. 


565 


Plants,  heat  of,  762;  circulation  in,  540-548; 

respiration  in,  84,  641,  642;  reproduction 

in,  781-784. 
Pneumogastric  nerve,  see  Par  Vagum. 
Polypes,  digestive  process  in,  443-445. 
Posterior  Pyramids,  893. 
Pregnancy,  duration  of,  825,  826. 
Prehension  of  food,  896. 
Presbyopia,  958. 
Primary  membrane,  206-209. 
Proteine,  168-173. 

Puberty,  in  male,  788;  in  female,  798. 
Pulp  of  hair,  328,  330. 
Pulp  of  teeth,  310,  313. 
Pulsations  of  heart,  579. 
Pulse,  in  arteries,  583,584;  respiratory,  in 

veins,  607. 
Pupil,  changes  in  diameter  of,  969. 
Pus,  632,  636,  637. 
Pyramids,  anterior,  890. 
«         posterior,  893. 


R 


Radiata,  Nervous  System  of,  849. 
Receptaculum  Chyli,  497. 
Reduction  of  food,  provisions  for,  445. 
Reflex  actions,  nature  of,  392-396. 

«  "         of  Articulata,    858—860;    of 

Mollusca,  851,  854;  of  Ver- 
tebrata,  875-879. 
Repkoduction,  general  nature  of  the  pro- 
cess, 778,  780. 
«  in  Plants,  781-784. 

Reproductive  cells,  240. 
Reptiles,  circulation  in,  562,  563;  lymphatic 
system  in,  500;    respiration  in,  668-671; 
nervous  centres  in,  871. 
Respiration,  nature  of  the  process,  641-642. 
"  organs  of,  in  lowest  animals, 

653;  in  Mollusca,  654-656; 
in  Annelida,  657 ;  in  Crusta- 
cea, 658;  in  Insects,  659- 
660;  in  Spiders,  661;  in  Fish- 
es, 663-667;  in  Reptiles,  668 
-671;  in  Birds,  672-674;  in 
Mammalia  and  Man,  675- 
688. 
**  chemical  phenomena  of,  689- 

702. 
«  insufficient,  effects  of,  703-709. 

Respiratory  movements,  680-682;  frequency 

of,  683. 
Respiratory  nerves,  in  Insects,  862 ;  in  Mol- 
lusks,  850-853;    in  Vertebrata,  684-688, 
895. 
Respiratory  palse,  607. 
Restiform  bodies,  892. 
Retina,  general  structure  of,  960. 
Rigor  Mortis,  367-369. 
Ruminating  stomach,  457. 


S 


Saccharine  compounds  in  food,  430-434, 493. 
Salivary  glands,  465. 

«       secretion,  446,  466,  467. 


Satiety,  sense  of,  486. 

Sebaceous  follicles,  747,  748. 

Secreting  cells,  238,  239,  712-714. 

Secretion,  nature  of  the  process,  710-713. 
"  effects  of  suppression  of,  711. 

Selecting  power  of  individual  parts,  612-615. 

Semicircular  canals,  952. 

Sensation,  389,  390;  nerves  of,  389,  391,900, 
901;  general  and  special,  932. 

Sensations,  regulation  of  muscular  movement 
by,  904. 

Sensorium,  390. 

Sensory  Ganglia,  900,  901;  functions  of,  902- 
908. 

Sensory  nerves,  909. 

Serous  Membranes,  197. 

Shell,  of  Echinodermata,  290,291;  of  Mol- 
lusca, 292-295;  of  Articulata,  296-298. 

Sight,  sense  of,  955-972. 

Single  vision  with  two  eyes,  963. 

Size  of  objects,  estimate  of,  968. 

Skin,  198,  204,  742-748,  940. 

Sleep,  921. 

Smell,  sense  of,  946-948. 

Sneezing,  948. 

Solen,  nervous  system  of,  852,  853. 

Somnambulism,  923. 

Sounds,  propagation  of,  949;  qualities  of,  954 

Sounds  of  heart,  571-575. 

Speech,  981,  982. 

Spermatic  fluid,  786,  787;  emission  of,  790. 

Spermatozoa,  240,  787;  use  of,  in  fecunda- 
tion, 804. 

Sphinx  ligustri,  nervous  system  of,  856,  857. 

Spiders,  respiratory  organs  of,  661. 

Spinal  Cord,  867,  868;  structure  of,  880-883; 
reflex  actions  of,  874-879,  884;  disordered 
states  of,  885-887. 

Spinal  accessory  nerve,  580,  888. 

Spinal  nerves,  origin  of,  880,  882. 
«  "       peculiar,  888. 

Spiracles  of  Insects,  659. 

Spleen,  structure  of,  506;  uses  of,  507-509. 

Stammering,  983,  984. 

Starchy  compounds  in  food,  430-432. 

Star-fish,  nervous  system  of,  849. 

Stearine,  261. 

Stereoscope,  964,  965. 

Stomach,  447,  448;  movements  of,  456-459. 
"         in  Ruminants,  457. 

Stomato-gastric  nerves  of  Invertebrata,  863. 
"  "       of  Vertebrata,  896. 

Strabismus,  963. 

Suction,  act  of,  896. 

Sudoriparous  glandulsB,  743,  744. 

Supra-renal  capsules,  510. 

Sympathetic  System,  in  Man,  ftinctions  of, 
926-929. 
'^  *'         traces   of,  among  In- 

vertebrata, 864. 

Syncope,  581,  628. 

Synovial  membranes,  197. 


T 

Tadpole,  respiration  of,  670 ;  metamorphosis 

of,  670. 
Taste,  nerves  of,  944. 


566 


INDEX. 


Taste,  sense  of,  945. 

Teeth,  structure  and  development  of,  310-327. 

Temperature,  sense  of,  933,  942. 

Testis,  structure  of,  785,  786. 

Tetanus,  886. 

Thalami  Optici,  901. 

Thirst,  488. 

Thoracic  duct,  497. 

Thymus  Gland,  511. 

Thyroid  Gland,  613. 

Tickling,  907. 

Tongue,  papillae  of,  943. 

Tonicity  of  arteries,  365,  684;    of  muscle, 

364-366. 
Torpedo,  electricity  of,  771-774. 
Torpidity,  induced  by  cold,  136;  by  want  of 

moisture,  158-161. 
Touch,  sense  of,  939-942. 
Tubercula  quadrigemina,  873,  900. 
Tubercular  diathesis,  626,  638,  639. 
Tunicata,  nervous  system  of,  850,  851. 
Tympanum,  951. 


U 


Ulceration,  635. 
Urea,  730,  731. 
Uric  acid,  732,  733. 


Urine,  composition  and  properties  of,  729- 
741;  effects  of  suppression  of,  741. 


Vascular  area,  551,  813,  814. 

Vegetation,  influence  of  light  upon,  79-92; 

influence  of  Heat  upon,  98-107. 
Veins,  movement  of  blood  in,  605-610. 
Venous  congestion,  609,  610. 
Villi  of  mucous  membrane,  241,  242. 
Vitreous  body  of  eye,  276. 
Vocal  ligaments,  974-979. 
Voice,  production  of,  973-979. 
Vowel  sounds,  production  of,  981. 


W 

Waste  or  disintegration  of  tissues,  361,  384, 

617. 
White  fibrous  tissue,  189,  190. 
Worm  tribes,  circulation  in,  552;  respiration 

in,  657. 

Yellow  fibrous  tissue,  189,  192. 
Zona  pellucida,  802. 


THE    END. 


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ELEMENTS  OF  PHYSIOLOGY, 

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With  One  Hundred  and  Eighty  Illustrations. 
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ON 


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PRINCIPLES 

OF 

GENERAL  AND  COMPARATIVE  PHYSIOLOGY, 

Intended  as  an  Introduction  to  the  Study  of  Human  Physiology  and  as  a 

Guide  to  the  Philosophical  Pursuit  of  Natural  History. 

BY  W.  B.  CARPENTER,  M.  D.,  F.  R.  S.,  &c.  &c. 

FROM  THE  SECOND  LONHON  EDITION. 

With  Alterations  and  Further  Improvements  by  the  Author. 

IN  ONE  VERY  NEAT  OCTAVO  VOLUME. 

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*'This  is  an  admirable  work,  and  will  give  Dr.  Carpenter  a  high  rank  among  the  cultiva- 
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A  xNEW  EDITION  OF 

CARPENTER'S  HUMAN  PHYSIOLOGY, 

REVISED    AND    BinCH    IMPROVED. 


PRINCIPLES  OF  HUMAN  PHYSIOLOGY, 

WITH  THEIR  CHIEF  APPLICATIONS  TO 

PATHOLOGY,  HYGIENE,   AND    FORENSIC   MEDICINE. 
BY  WILLIAM  B.  CARPENTER,  M.D.,  F.R.S.,  &c. 

SECOND  AMERICAN,  FROM  A  NEW  AND  REVISED  LONDON  EDITION. 

WITH  NOTES  AND  ADDITIONS, 

BY  MEREDITH  CLYMER,  M.D.,  &c. 

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In  one  octavo  volume,  of  about  650  closely  and  beautifully  printed  pages. 

The  very  rapid  sale  of  a  large  impression  of  the  first  edition  is  an  evidence  of  the  merits  of  this 
valuable  work,  and  that  it  has  been  duly  appreciated  by  the  profession  of  this  country.  The  publish- 
ers hope  that  the  present  edition  will  be  found  still  more  worthy  of  approbation,  not  only  from  the  ad- 
ditions of  the  author  and  editor,  but  also  from  its  superior  execution,  and  the  abundance  of  its  illustra- 
tions. No  less  than  eighty-five  wood -cuts  and  another  lithographic  plate  will  be  found  to  have  been 
added,  affording  the  most  material  assistance  to  the  student. 

"  We  have  much  satisfaction  in  declaring  our  opinion  that  this  work  is  the  best  systematic  treatise 
on  physiology  in  our  own  language,  and  the  best  adapted  for  the  student  existing  in  any  language." — 
Medico-Chirurgical  Review. 

"This  work  as  it  now  stands  is  the  only  Treatise  on  Physiology  in  the  English  language  which  ex- 
hibits a  clear  and  connected,  and  comprehensive  view  of  the  present  condition  of  that  science. 

"  Few  individuals  could  have  been  found  so  well  qualified  as  Dr.  Carpenter  for  acting  as  the  histo- 
rian of  physiological  science.  He  is  endowed  with  great  perseverance  and  industry,  possesses  a  clear 
and  logical  judgment,  is  able  to  see  distinctly  the  salient  points  of  the  more  abstruse  and  disputed  doc- 
trines, has  excellent  powers  of  generalization,  and  can  express  his  thoughts  in  lucid  and  correct  lan- 
guage. In  explaining  the  general  doctrines  of  the  science,  or  in  describuig  the  phenomena  attending 
the  performance  of  individual  functions,  he  lays  before  the  reader  a  judicious  admixture  of  the  most 
trustworthy  facts,  with  the  inductions  to  which  they  lead,  which  cannot  fail  to  give  him  a  clear  con- 
ception of  each  subject  brought  under  his  notice.  When  he  ventures  upon  any  new  generalizations, 
he  never  indulges  in  dogmatical  and  bold  assertions,  but  proceeds  in  a  cautious  and  philosophical 
spirit;  this  cannot  fail  to  exercise  a  salutary  influence  upon  the  mind  of  the  student  by  repressing  that 
tendency  to  hypothetical  speculation  to  which  young  and  ardent  minds  are  so  prone.  He  omits  no  op- 
portunity of  pointing  out  how  the  physiological  facts  and  doctrines  he  is  discussing  may  be  employed 
in  furnishing  more  scientific  methods  of  treating  disease.^'— The  London^  Edinburgh  Monthly  Journal 
of  Medical  Sciences. 

"This  work  exhibits  all  the  mental  characteristics  of  Dr.  Carpenter;  great  knowledge  of  what  has 
been  done  by  others,  clearness  of  conception,  and  lucidness  of  arrangement.  Although  entitled 
'  Human  Physiology,'  many  of  its  details  are  on  Histology  and  Histogeny,  or  the  minute  anatomy^  and 
development  of  tissues  which  man  possesses  in  common  with  the  rest  of  the  animated  creation.  They, 
however,  who  are  fond  of  such  investigations,  and  who  is  there  who  is  not  more  or  less  so,  will  find 
the  transcendental  as  well  as  the  more  sober  views  of  modern  inquiries  well  depicted.^'''— Am.  Medical 
Library. 

"Though  the  resources  of  the  author's  comprehensive  mind  are  apparently  devoted  to  the  advance- 
ment of  new  beginners  in  study,  there  is  a  splendid  exhibition  of  the  powers  of  analysis,  an  uncommon 
degree  of  success  in  making  abstruse  objects  clear,  and  in  forcibly  impressing  upon  others  the  laws  of 
life  wKich  he  so  well  understands,  which  will  give  eclat  to  Dr.  Carpenter's  reputation  when  he  will  be 
insensible  to  praise.  All  who  can  afford  to  have  a  good  system  of  physiology  should  possess  this;  and 
those  who  are  able  to  keep  pace  with  the  progress  of  science  should  not  be  without  it.  There  are  618 
pages,  large  sized  octavo,  on  good  paper,  with  a  type  as  distinctly  made  as  it  can  be  executed.  No 
necessity  seems  to  exist  for  extracting  from  its  pages,  or  commenting  especially  on  any  particular  parts 
or  portions  of  the  volume,  because  it  is  presumed  that  all  who  can  will  avail  themselves  of  it.  Proba- 
bly this  improved  edition  does  not  cost  more  than  one-third  the  price  asked  for  it  in  England,  and  yet 
jt  rs  superior  in  very  many  respects."— ^osion,  Med.  ^  Surg.  Journal. 

"It  would  be  a  dereliction  ofour  bibliographical  duty  not  specially  to  mention  the  highly  meritorious 
work  of  Dr.  Carpenter  on  the  Principles  of  Human  Physiology,  a  work  to  which  there  has  been  none 
published  of  equal  value  in  the  department  of  which  it  treats,  embodying,  as  it  does,  an  immense  store 
of  facts  and  modern  discoveries  in  anatomy  and  physiology  down  to  the  present  time."— Dr.  .B/ac^'s 
Retrospective  Address. 

"  It  is  a  clear  compendious  r^sumfe  of  the  existing  state  of  Physiological  Science,  conceived  and  ex- 
ecuted in  a  genuine  philosophical  spirit,  and  peculiarly  adapted  to  the  medical  student.  All  the  received 
facts  of  physiology  are  presented  in  a  well  digested  form  and  lucid  manner,  and  the  deductions  made 
from  them  show  close  reasoning,  and  a  very  impartial  spirit.  The  author,  though  still  a  young  man, 
has  already  won  a  high  reputation  in  this  department  of  medicine.  In  a  literary  point  of  view,  the 
present  work,  as  well  as  his  other  productions,  are  of  a  high  order;  his  style  is  clear  precise,  and  un- 
ostentatious, at  times  rising  to  positive  elegance."— Jllec/.  E.mminer. 


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vol.,  8vo.,  fancy  cloth,  with  many  cuts. 
Fownes'  Elementary  Work  on  Chemistry, 

1  vol.,  12mo.,  many  cuts,  cloth  or  sheep. 
Grahame's  Colonial  History  of  the  United 

States,  2  vols.,  8vo.,  a  new  edition. 
Grote's  History  of  Greece,  8vo.,  cloth,  [pre- 
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Giesler's  Ecclesiastical  History,  3  vols.  Svo. 
Griffith's  Chemistry  of  the  Four  Seasons, 

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Hawker  on  Shooting,  Edited  by  Porter,  one 

beautiful  8vo.  vol.,  rich  extra  cloth,  plates. 


MISCELLANEOUS  WORKS  PUBLISHED  BY  LEA  AND  BLANCHARD. 


Hale's  Ethnography  and  Philology,  impe- 
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Herschell's  Treatise  on  Astronomy,  1  vol., 
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Hemans'  Complete  Poetical  Works,  in  7 
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Holthouse's  Law  Dictionary,  with  large  ad- 
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Tngersoll's  History  of  the  Late  War,  1  vol., 

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KiRBY  ON  Animals,  1  vol.,  8vo.,  plates. 
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himself  to  prevent  or  control  insanity." 
No.  4,  "An  Introduction  to  Practical 
Organic  Chemistry."  No.  5,  "A  Brief 
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Wiieaton's  Elements  OF  International  Law, 
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TO   THE   MEDICAL  PROFESSION. 

The  following  list  embraces  works  on  Medical  and  other  Sciences  issued  by  the  subscrib- 
ers. They  are  to  be  met  wiih  at  all  the  principal  bookstores  throughout  the  Union,  and  will 
be  found  as  low  in  price  as  is  consistent  with  the  correctness  of  their  printing,  beauty  of  exe- 
cution, illustration  and  durability  of  binding.  No  prices  are  here  mentioned,  there  being  no 
fixed  standard,  as  it  is  evident  that  books  cannot  be  retailed  at  the  same  rate  in  New  Orleans 
or  Chicago  as  in  Philadelphia.  Any  information,  however,  relative  to  size,  cost,  &c.,  can 
be  had  on  applicatioR,  free  of  postage,  to  the  subscribers,  or  to  any  of  the  medical  book- 
sellers throughout  the  country. 

I.EA  &  BtAXCHARD,  Philadelphia. 


DICTIONARIES  AND  JOURNALS. 
American  Journal  of  the  Medical  Sciences,  quar- 
terly, at  $5  a  year. 
Cyclopaedia  of  Practical   Medicine,  by  Forbes, 
Tweedie,  &c.,  edited  by  Dunglison,  in  4  super 
royal  volumes,  3154  double  columned  pages. 
Dunglison's  Medical  Dictionary,  6th  ed.,   1  vol. 
imp.8vo.,804  large  pages,  double  columns. 
Hoblyn's  Dictionary  of  Medical  Terms,  by  Hays, 
1  vol.  large  12mo.,  402  pages,  double  columns. 
Medical  News  and  Library,  monthly  at  $1  a  year. 

ANATOMY. 
Anatomical  Atlas,  by  Smith  and  Horner,  large 

imp.  8vo.,  650  figures. 
Horner's  Special    Anatomy  and  Histology,  7th 

edition,  2  vols.  8vo.,  many  cuts,  1130  pages. 
Horner's   United  States  Dissector,  1  vol.  large 

royal  12mo.,  many  cuts,  444  pages. 
Wilson's  Human  Anatomy,  by  Goddard,  3d  edi- 
tion, I  vol.  8vo.,  235  wood-cuts,  620  pages. 
Wilson's   Dissector,  or  Practical   and   Surgical 
Anatomy,  with  cuts,  1  vol.  12mo.,  444  pages. 
PHYSIOLOGY. 
Carpenter's  Principles  of  Human  Physiology,  1 

vol.  8vo.,  644  pages,  many  cuts,  2d  edition. 
Carpenter's  Elements,  or  Manual  of  Physiology, 

1  vol.  8vo.,  666  pages,  many  cuts. 
Connection  between  Physiology  and  Intellectual 
Science,  1  vol.  18mo.,  paper,  price  25  cents. 
Dunglison's  Human  Physiology,  6th   edition,  2 

vols.  8vo.,  1350  pages,  and  370  wood-cuts. 
Harrison  on  the  Nerves,  1  vol.  8vo.,  292  pages. 
MUller's  Physiology,  by  Bell,  I  vol.  8vo.,886pp. 
Roget's  Outlines  of  Physiology,  8vo.,  516  pages. 
Todd  and  Bowman's  Physiological  Anatomy  and 
Physiology  of  Man,  with  numerous  wood-cuts. 
(Publishing  in  the  Medical  News.) 
PATHOLOGY. 
Andral  on  the  Blood,  I  vol,  small  8vo.,  120  pages. 
Abercrombie  on  the  Stomach,  new  edition,  1  vol. 

8vo.,  320  pages. 
Abercrombie  on  the  Brain,  new  edition,  1  vol. 

8vo.,  324  pages. 
Alison's  Outlines  of  Pathology,  &c.,  1  vol.  8vo., 

420  pages. 
Berzelius  on  the  Kidneys  and  Urine,  8vo.,  180  pp. 
Bennet  on  the  Uterus,  1  vol.  12mo.,  146  pages. 
Budd  on  the  Liver,  1  vol.  8vo.,  392  pages,  plates 

and  wood-cuts. 
Billing's  Principles,  1  vol.  8vo.,  304  pages. 
Bird  on  Urinary  Deposits,  8vo.,  228  pages,  cuts. 
Hasse's  Pathological  Anatomy,  8vo.,  379  pages. 
Hope  on  the  Heart,  by  Pennock,  a  new  edition, 

with  plates,  1  vol.  8vo.,  572  pages. 
Hughes  on  the  Lungs  and  Heart,  1  vol.  12mo., 

270  pages,  with  a  plate. 
Philip  on  Protracted  Indigestion,  8vo.,  240  pp. 
Philips  on  Scrofula,  1  vol.  8vo.,  350  pages. 
Prout  on  the  Stomach  and  Renal  Diseases,  1  vol. 

8vo.,  466  pages,  colored  plates. 
Ricord  on  Venereal,  new  ed.,  1  vol.  8vo,,  256  pp. 
Vogel's  Pathological   Anatomy   of   the   Human 
Body,   1  vol.  8vo.,  536  pages,  col.  plates. 


Walshe  on  the  Lungs,  1  vol.  12mo.,  310  pages. 
Wilson  on  the  Skin,  1  vol.  Svo.,  370  pages. 
Williams'  Pathology,  or  Principles  of  Medicine, 

1  vol.  8vo.,  384  pages. 
Williams  on  the  Respiratory  Organs,  by  Clyraer, 

1  vol.  8vo.,  500  pages. 

PRACTICE  OF  MEDICINE. 
Ashwell  on  the  Diseases  of  Females,  by  Goddard, 

1  vol.  8vo.,  520  pages. 
Benedict's  Compendium  of  Chapman's  Lectures, 

1  vol.  8vo.,  258  pages. 
Chapman  on  Thoracic  and  Abdominal  Viscera, 

&c.,  1  vol.  8vo.,  384  pages. 
Chapman  on  Fevers,  Gout,  Dropsy,  &c.  &c.,  1  vol, 

8vo.,  450  pages. 
Colombat  do  L'Isbre  on  Females,  translated  and 

edited  by  Meigs,  1  vol.  Svo. ,  720  pages,  cuts. 
Condie  on  the  Diseases  of  Children,  2d  edition,  I 

vol.  8vo.,  658  pages. 
Churchill  on  the  Diseases  of  Females,  by  Huston, 

4lh  edition,  1  vol.  8vo.,  604  pages. 
Clymer  and   others  on  Fevers,  a  complete  work 

in  1  vol.  Svo.  600  pages. 
Dewees  on  Children,  9th  ed.,  1  vol.  8vo.,  548  pp. 
Dewees  on  Females,  8th  edition,  1  vol.Svo.,  532 

pages,  with  plates. 
Dunglison's  Practice  of  Medicine,  2d  edition,  2 

vols.  8vo.,  1322  pages. 
Esquirol   on   Insanity,  by  Hunt,  Svo.  496  pages. 
Thomson  on  the  Sick  Room,  &c.,   1  vol.  large 

12mo.,  360  pages,  cuts. 
Watson's  Principles  and  Practice  of  Physic,  2d 

edition  by  Condie,  1  vol.  8vo.,  1060  large  pages. 

SURGERY. 

Brodie  on  Urinary  Organs,  1  vol.  Svo. ,  214  pages. 

Brodie  on  the  Joints,  1  vol.  Svo.  216  pages. 

Brodie's  Lectures  on  Surgery,  1  vol.  8vo.,  350  pp. 

Chelius'  System  of  Surgery,  by  South  and  Norris, 
in  3  large  Svo.  vols.,  near  2000  pages,  or  in  17 
parts  at  50  cents  each. 

Cooper  on  Dislocations,  and  Fractures,  1  vol.  Svo. 
500  pages,  many  cuts. 

Cooper  on  Hernia,  1  vol.  imp.  8vo,,  428  pp.,  pl'ts. 

Cooper  on  the  Testis  and  Thymus  Gland,  1  vol. 
imperial  Svo.  many  plates. 

Cooper  on  the  Anatomy  and  Diseases  ofthe  Breast, 
Surgical  Papers,  &c.  &c.,  I  vol.  imp.  8vo.,  pl'ts. 

Druitt's  Principles  and  Practice  of  Modern  Sur- 
gery, 3d  ed.,  1  vol.  Svo. ,534  pages,  many  cuts. 

Durlacher  on  Corns,  Bunions,  &c.  12mo.,  134  pp. 

Fergusson's  Practical  Surgery,  1  vol.  8vo.,  2d 
edition,  640  pages,  many  cuts. 

Guthrie  on  the  Bladder,  Svo.,  150  pages. 

Harris  on  the  Maxillary  Sinus,  Svo.,  166  pp. 

Jones'  (Wharton)  Ophthalmic  Medicine  and  Sur- 
gery, by  Hays,  1  vol.  royal  12mo.,529  pages, 
many  cuts,  and  plates  plain  or  colored. 

Liston's  Lectures  on  Surgery,  by  MUtter,  1  vol. 
Svo.,  566  pages,  many  cuts. 

Lawrence  on  the  Eye,  by  Hays,  new  edition, 
much  improved,  863  pages,  many  cuts  &  plates. 

Lawrence  on  Ruptures,  1  vol.  Svo.  480  pages. 

Miller's  Principles  of  Surgery,  1  vol.  Svo.,  526  pp. 


LEA  &  BLANCHARD'S  PUBLICATIONS. 


Miller's  Practice  of  Surgery,  1  vol.  8vo.,  496  pp. 
Maury's  Dental  Surgery,  1  vol.  8vo.,  286  pages, 

many  plates  and  cuts. 
Robertson  on  the  Teeth,  1  vol.  8vo.,  230  pp.  pts. 

MATERIA  MEDICA  AND  THERAPEUTICS. 
Dunglison's  Materia  Medica  and  Therapeutics,  a 

new  ed.,  with  cuts,  2  vols.  8vo.,  986  pages. 
Dunglison  on  New  Remedies,  5th  ed.,  I  vol.Svo., 

653  pages. 
Ellis'  Medical  Formulary,  8th  ed.,  much  improv- 
ed, 1  vol.  8vo.,  272  pages. 
Griffith's  Medical  Botany,  a  new  work,  1  large 

vol.  8vo.,  with  over  350  illustrations. 
Pereira's  Materia  Medica  and  Therapeutics,  by 

Carson,   2d   edition,  2  vols.  Svo.,   1580  very 

large  pages,  nearly  300  wood-cuts. 
Royle's  Materia  Medica  and   Therapeutics,  by 

Carson,  1  vol.  8vo.,  689  pages,  many  cuts. 

OBSTETRICS. 

Churchill's  Theory  and  Practice  of  Midwifery,  by 

Huston,  2d  ed,,  1  vol.  8vo.,  520  pp.,  many  cuts. 
Dewees'  System  of  Midwifery,  lith  ed.,  1  vol. 

Svo.  660  pages,  with  plates. 
Rigby's  System  of  Midwifery,  1  vol.  Svo.  492  pp. 
Ramsbotham  on  Parturition,  with  many  plates,  1 

large   vol.  imperial  8vo.,   new  and  improved 

edition,  520  pages. 

CHEMISTRY  AND  HYGIENE. 
Brighamon  Excitement, &c.,  1  vol.  12mo.,  204  pp. 
Dunglison  on  Human  Health,  2d  ed.,8vo.,  464  pp. 
Fowne's  Elementary  Chemistry  for  Students,  1 

vol.  royal  12mo.,  460  large  pages,  many  cuts. 
Graham's  Elements  of  Chemistry,  I  vol.  8vo.,  750 

pages,  many  cuts. 
Griffith's  Chemistry  of  the  Four  Seasons,  1  vol. 

royal  12mo.,  451  pages,  many  cuts. 
Practical  Organic  Chemistry,  18mo.,  paper,  25  cts. 
Simon's  Chemistry  of  Man,  8vo.,  730  pp.,  plates. 

MEDICAL  JURISPRUDENCE,  EDUCATION, 

&c. 
Bartlett's  Philosophy  of  Medicine,  1  vol.  8vo., 
312  pages. 


Dunglison's  Medical  Student,  2d  ed.l2mo., 312  pp. 
Man's  Power  over  himself  to  Prevent  or  Control 

Insanity,  ISnio.  paper,  price  25  cents. 
Taylor's  Medical  Jurisprudence,  by  Griffith,   1 

vol.  8vo.,  540  pages. 
Traill'sMedical  Jurisprudence,!  vol.Svo.  234pp. 

NATURAL  SCIENCE,  &c. 
Arnott's  Elements  of  Physics,  new  edition,  1  vol. 

8vo.,  484  pages,  many  cuts. 
Brewster's  Treatise  on  Optics,  I  vol.  12mo.,  423 

pages,  many  cuts. 
Babbage's  "  Fragment,"   1  vol.  8vo.,  250  pages. 
Buckland's  Geology  and  Mineralogy,  2  vols.  8vo., 

with  numerous  plates  and  maps. 
Bridgewater  Treatises,  with   many  plates,  cuts, 

maps,  &c.,  7  vols.  8vo.,  3287  pages. 
Carpenter's  Popular  Vegetable  Physiology,  1  vol. 

royal  12mo.,  many  cuts. 
Hale's  Ethnography  and  Philology  of  the  U.  S. 

Exploring  Expedition,  in  1  large  imp.  4to.  vol. 
HerschelTs  Treatise  on  Astronomy,  1  vol.  12mo. 

417  pages,  numerous  plates  and  cuts. 
Introduction  to  Vegetable  Physiology,  founded 

on  the  works  of  De  Candolie,  Lindley,  &c., 

ISmo.,  paper,  25  cents. 
Kirby  on  Animals,  plates,  1  vol.Svo.,  520  pages. 
Kirby  and  Spence's  Entomology,  from  6th  Lon- 
don ed.,  1  vol.  8vo.,  600  large  pages;  plates, 

plain  or  colored. 
Philosophy  in  Sport  made  Science  in  Earnest,  1 

vol.  royal  18mo.,  430  pages,  many  cuts. 
Roget's  Animal  and  Vegetable  Physiology,  with 

400  cuts,  2  vols.  Svo.,  872  pages.     ^ 
Trimmer's  Geology  and  Mineralogy,  1  vol.  Svo., 

528  pages,  many  cuts. 

VETERINARY  MEDICINE. 
Claterand  Skinner's  Farrier,  1  vol.  12mo.,220  pp. 
Youatt's  Great  Work  on  the  Horse,  by  Skinner, 

1  vol.  8vo.,  448  pages,  many  cuts. 
Youatt  and  Clater's  Cattle  Doctor,  1  vol.  12mo., 

282  pages,  cuts. 
Youatt  on  the  Dog,  by  Lewis,  1  vol.  demy  8vo., 

403  pages,  beautiful  plates. 


XE"W  MEDICAIi  AMD  SCIENTIFIC  BOOKS. 

Lea  Sf  Blanchard  have  at  press  and  preparing  for  publication  thefoUowing  works. 

Carpenter's  Comparative  Anatomy  and  Physiology,  revised  by  the  author,  with  beautiful  steel  plates. 

A  New  Work  on  the  Diseases  and  Surgery  of  the  Ear,  with  illustrations. 

Bird's  Natural  Philosophy,  from  a  new  Lond.  ed.,  in  1  vol.  royal  12mo.  with  wood-cuts. 

Youatt  on  the  Pig,  a  new  work  with  beautiful  illustrations  of  all  the  different  varieties. 

Maunder's  Treasury  of  Natural  History,  a  Popular  Dictionary  of  Animated  Nature,  with  illustrations. 

Dana  on  Corals,  imp.  4to,,  with  an  Atlas  of  Maps,  being  vols.  8  and  9  of  the  U.  S.  Ex.  Expedition. 

Churchill  on  the  Management  and  more  Important  Diseases  of  Infancy  and  Childhood,  in  1  vol.  Svo. 

Solly  on  the  Human  Brain,  its  Structure,  Physiology  and  Diseases. 

SpooNER  on  Sheep,  with  numerous  wood-cuts. 

Malgaigne's  Operative  Surgery,  with  numerous  wood-cuts. 

QuAiN's  Elements  of  Anatomy,  by  Dr.  Sharpey,  with  many  illustrations. 

De  La  Beche's  new  work  on  Geology,  with  numerous  wood-cuts. 

SouTHWooD  Smith's  Philosophy  of  Health. 

Kane's  Elements  of  Pharmacy,  with  additions,  in  1  vol.  12mo. 

The  Universal  Formulary  and  Pharmacy,  by  R.  E.  Griffith,  M.  D.,  in  1  vol.  Svo. 

An  Analytical  Compend  of  the  Various  Branches  of  Practical  Medicine,  Surgery  Anatomy,  Mid- 
wifery, Diseases  of  Women  and  Children,  MateriaMedica  and  Therapeutics,  Physiology,  Chemistry 
and  Pharmacy,  by  John  Neill,  M.  D.,  and  F,  Gurney  Smith,  M.  D.,  with  numerous  illustrations. 

Taylor's  Manual  of  Toxicology,  in  1  vol.     Metcalf  on  Caloric,  in  one  large  Svo.  volume. 

The  History,  Diagnosis  and  Treatment  of  Typhoid,  Typhus,  Bilious  Remittent,  Congestive  and 
Yellow  Fever,  by  Elisha  Bartlett,  M.  D.,  &c.,  being  a  new  and  extended  ed.  of  his  former  work. 

A  Cyclopedia  of  Anatomy  and  Physiology,  based  on  the  large  work  of  Todd,  in  2  vols,  large  Svo. 

The  Universal  Dispensatory,  with  many  wood-cuts,  in  1  large  Svo.  volume. 

A  New  Work  on  Bandaging,  and  other  Points  of  Minor  Surgery,  in  1  vol.  12mo.,  with  wood-cuts. 

Elements  of  General  Therapeutics,  &c.,  by  Alfred  Stillfe,  M.D.,  in  1  vol.  Svo. 

CoATES'  Popular  Medicine,  a  new  edition,  fully  revised  and  brought  up,  in  1  vol.  large  12mo. 

Professor  Meigs'  New  Work  on  Females ;  their  Diseases  and  their  Remedies,  in  a  Series  of  Let* 
ters  to  his  Class,  in  I  vol.  Svo. 

Together  with  various  other  works. 


LEA  &  BLANCHARD'S  PUBLICATIONS. 


NOW  OOMPLEIE. 

THE     GREAT    SURGICAL    LIBRARY. 

A  SYSTEM  "OF  SURGERY. 

BY    J.    M.    CHELIUS, 

Doctor  in  Medicine  and  Surgery,  Public  Professor  of  General  and  Ophthalmic  Surgery,  etc.  etc.  in  the  Uni- 
versity of  Heidelberg. 

TRANSLATED  FROM  THE  GERMAN, 

AND  ACCOMPANIED  WITH  ADDITIONAL  NOTES  AND  OBSERVATIONS, 
BY    JOHN    F.    SOUTH, 

Surgeon  to  St.  Thomas'  Hospital. 
EDITED,  WITH  REFERENCE  TO  AMERICAN  AUTHORITIES, 
BY  GEORGE  W.  NORRIS,  M.  D. 
Now  complete  in  three  large  octavo  volumes  of  over  six  hundred  pages  each,  or  in  17  numbers,  at  fifty  cents. 
This  work  has  been  delayed  beyond  the  time  originally  promised  for  its  completion,  by  the  very  extensive 
additions  of  the  translator.    In  answer  to  numerous  inquiries,  the  publishers  now  have  the  pleasure  to  pre- 
sent it  in  a  perfect  state  to  the  profession,  forming  three  unusually  large  volumes,  bound  in  the  best  manner, 
and  sold  at  a  very  low  price. 

This  excellent  work  was  originally  published  in  Germany,  under  the  unpretending  title  of  "Handbook  to 
the  Author's  Lectures."  In  passing,  however,  through  six  successive  editions,  it  has  gradually  increased 
in  exlent  and  importance,  until  it  now  presents  a  complete  view  of  European  Surgery  in  general,  but  more 
especially  of  English  practice,  and  it  is  acknowledged  to  be  well  fitted  to  supply  the  admitted  want  of  a  com- 
plete and  extended  system  of  Surgery  in  all  its  branches,  comprehending  both  the  principles  and  the  prac- 
tice of  this  important  branch  of  the  healing  art.  Since  Benjamin  Bell's  great  work,  first  published  in  1783, 
and  now  almost  obsolete,  no  thorough  and  extended  work  has  appeared  in  the  English  language,  occupying 
the  ground  which  this  is  so  well  calculated  to  cover. 

The  fact  of  this  work  being  carried  to  six  editions  in  Germany,  and  translated  into  no  less  than  eight  lan- 
guages, is  a  sufficient  evidence  of  the  ability  with  which  the  author  has  carried  out  his  arduous  design. 

This  translation  has  been  undertaken  with  the  concurrence  and  sanction  of  Professor  Chelius.  The  trans- 
lator, Mr.  John  F.  South,  appears  1o  have  devoted  himself  to  it  with  singular  industry  and  ardor,  and  to  have 
brought  it  up  almost  to  the  very  hour  of  publication  His  notes  and  additions  are  very  numerous,  embodying 
the  results  and  opinions  of  all  the  distinguished  surgeon^  of  the  day,  Continental,  English  and  American. 
The  leading  opinions  of  .John  Hunter,  on  which  Modern  English  Surgery  has  been  raised,  are  set  forth  ;  the 
results  of  the  recent  microscopical  discoveries,  esi)ecially  in  reference  to  infiammaiion,  will  be  found  here, 
together  with  many  other  practical  observations,  placing  the  work  on  a  level  with  the  present  slate  of  Sur- 
gery, and  rendering  it  peculiarly  useiul,  both  to  the  student  and  practitioner. 

The  labors  of  the  English  translator  have  been  so  numerous  and  important,  that  there  is  but  little  which 
remains  to  be  supplied  by  the  American  editor.  Dr.  G.  W.  Norris  has  consented,  howeverj  to  superintend 
the  passage  of  the  workj  through  the  press,  and  supply  whatever  may  have  been  omitted  in  relation  to  the 
Surgical  Literature  oflhis  country. 

The  Medical  Press  and  profession,  both  in  England  and  in  this  country,  have  joined  ia 
praise  of  this  great  work, as  being  more  complete  than  any  other,  and  as  affording  a  compiete 
library  of  reference,  equally  suited  to  the  practitioner  and  to  the  student. 

"  We  strongly  recommend  all  surgical  practitioners  and  students,  who  have  not  yet  looked  into  this  work, 
to  provide  themselves  with  it  without  delay,  and  study  its  pages  diligently  and  deliberately." — The  Edin- 
burgh Medical  and  Surgical  Journal. 

•'Judging  from  a  single  number  only  of  this  work,  we  have  no  hesitation  in  saying'that,  if  the  remaining 
portions  correspond  at  all  with  the  first,  it  will  be  by  far  the  most  complete  and  scientific  System  of  Surgery 
in  the  English  language.  We  have,  indeed,  seen  no  work  which  so  nearly  comes  up  to  our  idea  of  what 
such  a  procUiclion  should  be.  both  as  a  practical  guide  and  as  a  work  of  reference,  as  this ;  and  the  fact  that 
it  has  passed  through  six  editions  in  Germany,  and  been  translated  into  seven  languages,  is  sufficiently.con- 
vjncing  proof  of  its  value.  It  is  methodical  and  concise,  clear  and  accurate,  omitting  all  minor  details  and 
fruitless  speculations,  it  gives  us  ail  the  information  we  want  in  the  shortest  and  simplest  form." — 2'Ae  New 
York  Journal  of  Medicine. 

'•  Nor  do  these  parts,  in  any  degree,  fall  short  of  their  predecessors,  in  the  copiousness  and  value  of  their 
details.  The  work  certainly  forms  an  almost  unique  curiosity  in  medical  literature,  in  the  fact  that  the 
notes  occupy  a  larger  portion  of  the  volume  than  the  original  matter,  an  arrangement  which  is  constantly 
appearing  to  render  the  text  subsidiary  to  its  illustrations.  Still  this  singularity  of  manner  does  not  at  all 
detract  from  the  value  of  the  matter  thus  disposed."— T^e  London  Medical  Gazette. 

'•This  work  has  long  been  the  chief  text-book  on  Surgery  in  the  principal  schools  of  Germany,  and  the 
publication  of  five  editions  of  it  in  the  original  and  of  translations  into  no  less  than  eight  foreign  languages, 
shows  the  high  estimation  in  which  it  is  held.  As  a  systematic  work  on  Surgery  it  has  merits  of  a  high  order. 
It  is  methodical  and  concise— and  on  the  whole  clear  and  accurate.  The  most  necessary  information  is 
conveyed  in  the  shortest  and  simplest  form.  Minor  details  and  fruitless  speculations  are  avoided.  It  is  in 
fact,  essentially  a  practical  book.  This  work  was  first  published  nearly  twenty  years  ago,  and  its  solid  and 
permanent  reputation  has  no  doubt  led  Mr.  South  to  undertake  the  present  translation  of  the  latest  edition 
of  it,  which,  we  are  informed,  is  still  passing  through  the  press  in  Germany.  We  should  have  felt  at  a  loss 
lo  select  any  one  better  qualified  for  the  task  than  the  translator  of  Otto's  Compendium  of  Human  and  Com- 
parative Pathological  Anatomy— a  surgeon  to  a  large  hospital  whose  industry  and  opportunities  have 
enabled  him  to  keep  pace  with  the  improvements  of  his  time."  — TAe  Medico-Chirurgical  Review. 

"  Although  Great  Britain  can  boast  of  some  of  the  most  skillful  surgeons,  both  amongjier  past  and  her  present 
professorsof  that  branch  of  medical  scieiice.no  work  professing  to  be  a  complete  system  of  Surgery  has  been 
published  in  the  British  dominions  since  that  of  Benjamin  Bell,  now  more  than  half  a  century  old. 

''This  omission  in  English  medical  literature  is  fully  and  satisfactorily  supplied  by  the  translation  of  Profes- 
scr  Chelius's  System  of  Surgery  by  agentleman  excellently  fitted  for  the  task,  both  by  his  extensive  reading, 
and  the  opportunities  of  practical  experience  which  he  has  enjoyed  for  years  as  surgeon  to  one  of  our  largest 
metropolitan  hospitals.  The  fact  of  Professor  Chelius's  work  having  been  translated  into  seven  languages  is 
wifficienl  proof  of  the  estimation  in  which  it  is  held  by  our  continental  brethren,  and  the  Engli.sh  Edition, 
now  in  course  of  publication,  loses  none  of  the  value  of  the  original  from  the  treatment  received  at  the  hands 
of  its  translator.  The  notes  and  additions  of  Professor  South  are  numerous,  and  contain  the  opinions  result- 
ing from  his  vast  experience,  and  from  that  of  his  colleague." — The  Medical  Times. 

"It  ably  maintains  the  character  formerly  given,  of  being  the  most  learned  and  complete  systematic 
treatise  now  extant  The  descriptions  of  surgical  diseases,  and  indeed  the  whole  of  the  pathological  depart- 
raent,  are  most  valuable."— TAe  Edinburgh  Medical  and  Siirgical  Journal. 

Ojr  Persons  wishing  this  work  sent  to  them  by  mail,  in  parts,  can  remit  Ten  Dollars,  for 
'Which  a  -»et  will  be  sent  by  the  publishers,  free  of  postage,  together  with  a  copy  of  "The 
j^edical  Jilews  and  Library"  for  one  year. 


LEA  &  BLANCHAED'S  PUBLICATIONS. 


GHEUUS'S  SURGERY,  CONTINUED. 

The  publishers  annex  a  very  condensed  summary  orthe  contents  of  Chelius's  Surgery,  showing 
the  complete  and  systematic  manner  in  which  the  whole  subject  is  divided  and  treated. 


I.  Division. — Of  Inflammation. 

1.  Qf  inflammation  in  general. 

2.  Qf  some  peculiar  kinds  of  inflammation. 

a.  Of  erysipelas ;  6.  Of  burns  ;  c.  Of  frost- 
bite ;  d.  Of  boils  ;  e.  Of  carbuncle. 

3.  Qf  inflammation  in  some  special  organs. 

a.  Of  inflammation  of  the  tonsils  ;  b.  Of  the 
parotid  gland  ;  c.  Of  the  breasts  ;  d.  Of 
the  urethra  ;  e.  Of  the  testicle  ;  /.  Of  the 
muscles  of  the  loins;  g.  Of  the  nail 
joints  ;  h.  Of  the  joints,  viz. 

a.  Of  the  synovial  membrane  ;  b.  Of  the  car- 
tilages ;  c.  Of  the  joint-ends  of  the  bones, 
viz.,  aa.  in  the  hip-joint;  66.  in  the 
shoulder-joint ;  cc.  in  the  knee-joint ; 
and  so  on. 
II.  Division. — Diseases  which  consist  in  a  dis- 
turbance of  physical  connexion. 

I.  Fresh  solutions  of  continuity. 

A.  Wounds  ;  B.  Fractures. 

II.  Old  solutions, 

A.  Which  do  not  suppurate,  viz. 

a.  False  joints  ;  6.  Hare-lip  ;  c.  Cleft  in 
the  soft  palate  ;  d.  Old  rupture  of 
the  female  perineum. 

B.  Which  do  suppurate,  viz. 
i.  Ulcers. 

1.  In  general. 

2.  In  particular. 

a.  Atonic  ;  6.  Scorbutic  ;  c.  Scrofulous  ; 
d.  Gouty  ;  e.  Impetiginous  ;  /.  Vene- 
real ;  g.  Bony  ulcers  or  caries. 
ii.  Fistulas. 

a.  Salivary  fistula  ;  6.  Biliary  fistula ;  c.  Faecal 
fistula  and  artificial  anus ;  d.  Anal  fistula ; 
e.  Urinary  fistula. 

III.  Solutions  of  continuity  by  changed  position  of 

parts. 
1.  Dislocations;  2.  Ruptures;  3.  Prolapses; 
4.  Distortions. 

IV.  Solutions  of  continuity  by  unnatural  distention. 

1.  In  the  arteries,  aneurisms  ;  2.  In  the  veins, 
varices ;  3.  In  the  capillary-vascular  sys- 
tem, teleangiectasis. 

III.  Division. — Diseases  dependent  on  the  unna- 
tural adhesion  of  parts. 

1.  Anchylosis  of  the  joint-ends  of  bones  ;  2.  Grow- 
ing together  and  narrowing  of  the  aperture 
of  the  nostrils  ;  3.  Unnatural  adhesion  of  the 
tongue ;  4.  Adhesion  of  the  gums  to  the 
cheeks;  5.  Narrowing  of  the  oesophagus  ;  6. 
Closing  and  narrowing  of  the  rectum ;  7. 
Growing  together  and  narrowing  of  the  pre- 
puce ;  8.  Narrowing  and  closing  of  the  ure- 
thra ;  9.  Closing  and  narrowing  of  the  vagina 
and  of  the  mouth  of  the  womb. 


IV.  Division. — Foreign  bodies. 

1 .  Foreign  bodies  introduced  externally  into  our 

organism. 
a.  Into  the  nose ;  6.  Into  the  mouth  ;  c.  Into 
the  gullet  and  intestinal  canal ;  d.  Into 
the  wind-pipe. 

2.  Foreign  bodies  formed  in  our  organism  by  the 

retention  of  natural  products. 

A.  Retentions  in  their  proper  cavities  and 

receptacles. 

a.  Ranula ;  6.  Retention  of  urine  ;  c. 
Retention  of  the  foetus  in  the  womb 
or  in  the  cavity  of  the  belly,  (Caesa- 
rean  operation,  section  of  the  pubic 
symphysis,  section  of  the  belly.) 

B.  Extravasation  external  to  the  proper  cavi- 

ties or  receptacles. 

a.  Blood  swellings  on  the  heads  of  new- 
born children;  6.  Haematocele;  c. 
Collections  of  blood  in  joints. 

3.  Foreign  bodies  resulting  from  the  accumulation 

of  unnatural  secreted  fluids, 
a.  Lymphatic  swellings  ;  6.  Dropsy  of  joints  ; 
c.  Dropsy  of  the  bursae  mucosae  ;  d.  Wa- 
ter in  the  head,  spina  bifida;  e.  Water 
in  the  chest  and  empyema; /.  Dropsy 
of  the  pericardium  ;  g.  Dropsy  of  the 
belly ;  h.  Dropsy  of  the  ovary  ;  i.  Hy- 
drocele. 

4.  Foreign  bodies  produced  from  the  concretion  of 

secreted  fluids. 

V.  Division. — Diseases  which  consist  in  the  de- 
generation of  organic  parts,  or  in  the  produc- 
tion of  new  structures. 

1.  Enlargement  of  the  tongue  ;  2.  Bronchocele  ; 
3.  Enlarged  clitoris;  4.  Warts;  5.  Bunions; 
6.  Horny  growths;  7.  Bony  growths  ;  8.  Fun- 
gus of  the  dura  mater;  9.  Fatty  swellings ; 
10.  Encysted  swellings;  11.  Cartilaginous 
bodies  in  joints;  12.  Sarcoma;  13.  Medul- 
lary fungus  ;  14.  Polypus ;  15.  Cancer. 

VI.  Division. — Loss  of  organic  parts. 

1.  Organic  replacement  of  already  lost  parts,  es- 

pecially of  the  face,  according  to  the  Taglia- 
cotian  and  Indian  methods. 

2.  Mechanical  replacement :  Application  of  arti- 

ficial limbs,  and  so  on. 

VII.  Division. — Superfluity  of  organic  parts. 

VIII.  Division. — Display  of  the  elementary  ma* 
nagement  of  surgical  operations. 

General  surgical  operations  :  Bleeding,  cupping, 
application  of  issues,  introduction  of  setons, 
amputations,  resections,  and  so  on. 


DRUITT'S  SURGERY.    New  Edition-Wow  Ready,  1847. 

THE  PRINCIPLES  AND  PRACTICE  OF  MODERN  SURGERY.. 

By    ROBERT    DRUITT,    Surgeon. 

THIRD  AMERICAN  FROM  THE  THIRD  LONDON  EDITION 
Illustrated  with  one  hundred  and  fifty-three  wood  engravings. 
WITH  NOTES  AND  COMMENTS, 
BY  JOSHUA  B.  FLINT,  M.D,  M.  M.,  S.  S.,  &c.  &c. 
In  One  very  neat  Octavo  Volume  of  about  Five  Hundred  and  Fifty  Pages. 
In  presenting  this  work  to  the  American  profession  for  the  third  time,  but  little  need  be  said  to  TwITcit  foir 
it  a  continuation  of  the  favor  with  which  it  has  been  received.    The  merits  which  have  procured  it  this 
favor,  its  clearness,  concisenesSj  and  its  excellent  arrangement,  will  continue  to  render  it  the  favorite  text- 
book of  the  student  who  wishes  in  a  moderate  space  a  compend  of  the  principles  and  practice  of  S«rgery. 

"This  work  merits  our  warmest  commendations,  and  we  strongly  recommexjd  it  to  young  surgcu>iL9  M  OT 
admirable  digest  of  the  principles  and  practice  of  modern  Surgery."— Merficai  GazeUi.  ■        -    .  -  •» 


LEA  &  BLANCHARD'S  PUBLICATIONS. 


SJOVT  READir. 


EOYLE'S  MATERIA  MEDICA. 


MATERIA  MEDICA  AND  THERAPEUTICS; 

INCLUDINa  THE  PREPARATIONS  OF  THE  PHARMACOPCEIAS  OF  LONDON, 
EDINBURGH,  DUBLIN,  AND  OF  THE  UNITED  STATES. 

WITH    MANY    NEW    MEDICINES. 

BY  J.  FORBES  ROYLE,  M.D,  F.  R.  S., 

Late  of  the  Medical  Staff  in  the  Bengal  Army,  Professor  of  Materia  Medica  and  Therapeutics,  King's  Col- 
lege, London,  &c.  &c. 

EDITED  BY  JOSEPH  CARSON,  M.D., 

Professor  of  Materia  Medica  in  the  Philadelphia  College  of  Pharmacy,  fcc.  &c. 

WITH  NINETY-EIGHT  ILLUSTRATIONS. 

l][j'  See  Specimen  of  the  Cut»f  but  not  of  the  Paper  or  Working^  on  next  Page* 

In  one  large  octavo  volume  of  about  700  pages. 

Being  one  of  the  most  beautiful  Medical  works  published  in  this  Country. 

The  want  has  been  felt  and  expressed  for  some  time,  of  a  text-book  on  Materia  Medica,  which 
should  occupy  a  place  between  the  encyclopaedic  works,  such  as  Pereira,  and  the  smaller  treatises 
which  present  but  a  meagre  outline  of  the  science.  It  has  been  the  aim  of  the  author  of  the 
present  work  to  fill  this  vacancy,  and  by  the  use  of  method  and  condensation,  he  has  been  enabled 
to  present  a  volume  to  the  student,  which  will  be  found  to  contain  what  is  necessary  in  a  complete 
and  thorough  text-book  of  the  science,  encumbered  with  few  unnecessary  details.  The  editor. 
Dr.  Carson,  has  added  whatever  was  wanted  to  adapt  it  to  the  Pharmacopoeia  of  the  United  States, 
and  it  is  confidently  recommended  to  the  student  and  practitioner  of  medicine,  as  one  of  the  best 
text-books  on  the  subject,  now  before  the  profession. — Great  care  has  been  taken  in  its  mechanical 
execution. 

"  Dr.  Royle's  manual,  while  it  has  the  convenience  of  being  in  a  portable  form,  contains  as  much 
matter  as  would  fill  two  octavo  volumes  in  large  type.  Our  readers  will  judge,  from  the  remarks 
which  we  have  already  made,  that  we  think  highly  of  this  work.  The  subject  is  well  treated,  the 
matter  practical  and  well  arranged,  and  we  do  not  hesitate  to  recommend  it  as  a  most  useful 
volume  to  the  student  and  practitioner.  It  is  a  good  specimen  of  typography,  and  the  engravings 
are  well  executed." — Medical  Gazette. 

In  regard  to  the  yet  more  essential  constituent,  the  literary  portion  of  the  work,  no  one  who  is 
acquainted  with  the  former  productions  of  Dr.  Royle,  will  doubt  that  the  author  has  discharged  his 
duties  with  the  same  skill  as  the  artist.  The  work  is,  indeed,  a  most  valuable  one,  and  will  fill  up 
an  important  gap  that  existed  between  Dr.  Pereira's  most  learned  and  complete  system  of  materia 
medica,  and  the  class  of  productions  at  the  other  extreme,  which  are  necessarily  imperfect  from 
tlieir  small  extent.  Such  a  work  as  this  does  not  admit  of  analysis  and  scarcely  of  detailed  critical 
examination.  It  would,  however,  be  injustice  to  the  learned  author  not  to  state  that,  in  addition 
to  what  former  works  on  the  subject  necessarily  contained,  the  reader  will  find  here  not  a  little 
that  is  either  original,  or  introduced  for  the  first  time,  more  especially  in  the  details  of  botany  and 
natural  history,  and  in  what  may  be  termed  the  archaeology  of  drugs. — The  British  and  Foreign 
Medical  Review. 

Of  the  various  works  that  have  from  time  to  time  appeared  on  materia  medica  on  the  plan  of  the 
one  before  us,  there  is  none  more  deserving  of  commendation.  From  the  examination  which  we 
have  given,  accuracy  and  perspicuity  seem  to  characterize  it  throughout,  as  a  text  book  of  refer- 
ence to  the  student  of  medicine,  and  especially  of  pharmacy  in  its  application  to  medicine,  none 
could  be  better. 

We  think  that  every  one  who  can  afford  it  should  possess  this  excellent  work,  the  value  of  which 
has  been  greatly  enhanced  by  the  additions  of  Dr.  Carson,  than  whom  no  one  is  more  competent 
to  estimate  it  correctly,  and  to  make  such  additions  as  may  adapt  it  for  American  service. — The 
Medical  Examiner. 

We  have  sufficiently  extended  our  notice  of  the  manual  of  materia  medica  and  therapeutics,  to 
show  that  it  possesses  great  merit,  which  will  be  a  pretty  sure  guarantee  of  its  acceptableness  to 
the  profession.  The  department  of  materia  medica  is  now  so  extended,  that  the  treatises  recently 
issued  from  the  press,  partake  of  the  nature  of  cyclopaedias.  To  the  student,  whether  of  pharmacy 
solely  or  medicine,  an  extended  manual  as  the  present  cannot  but  be  regarded  with  favor. — The 
.  American  Journal  of  Pharmacy. 

We  cannot,  however,  conclude  without  expressing  our  warm  approbation  of  the  volume  as  a 
whole.  It  will  certainly  not  detract  from  the  author's  high  reputation. — The  Medico-Chirurgical 
Review, 

Uj. 


1  ■    ■,         ,  » 


SPECIMEN   OF   CUTS   IN 

RO  YLE'S 

MATERIA  MEMCA  AND  THERAPEUTICS 


aAfl:mT."n!/ 


^m 


^u 


10  LEA  &  BLANCHARD'S  PUBLICATIONS. 

"  CHURCHILL'S  MIDWIFERY. 

ON  THE  THEORY  AND  PRACTICE  OF  MIDWIFERY. 

BY  FLEETWOOD  CHURCHILL,  M.  D.,  M.  R.  I.  A., 

Licentiate  of  the  College  of  Physicians  in  Ireland  ;  Physician  to  the  Western  Lying-in-Hospual ;  Lecturer  on 
Midwifery,  &c.,  in  the  Richmond  Hospital  Medical  School,  &c.  &.C. 
WITH  NOTES  AND  ADDITIONS, 
BY  ROBERT  HUSTON,  M.D., 
Professor  of  Materia  Medica  and  General  Therapeutics,  and  formerly  of  Obstetrics  and  the  Disease  of  Wo- 
men and  Children  in  the  Jefferson  Medical  College  of  Philadelphia;  President  of  the  Philadelphia 
Medical  Society,  &c.  &c. 
SECOND  AMERICAN  EDITION. 
WITH  ONE  HUNDRED  AND  TWENTY-EIGHT  irtUSTRATIONS, 
Engraved  by  Gilbert  from  Drawings  by  Bags  and  others. 
In  one  beautiful  octavo  volume. 
In  this  age  of  books,  when  much  is  written  in  every  department  of  the  science  of  medicine,  it  is  a  matter  of 
no  small  moment  to  the  student,  winch  of  the  many  he  shall  choose  for  his  study  in  pupilage,  and  guide  in 
practice.     In  no  department  is  the  choice  more  difficult  than  in  that  of  midwifery  ;  many  excellent  and  truly 
valuable  treatises  in  thisdepartment  of  medicine  have,  within  a  few  years  past,  been  written;  of  this  character 
are  ihose  of  Dewees,  Velpeau.  Meigs  and  R'gi)y,  with  due  refpect  to  the  auihorsoftlie  works  just  cited,  we  are 
compelled  to  admit,  thai  to  Mr.  Churchill  has  been  reserved  the  honorof  presenting  to  the  profession  one  more 
particularly  adapted  to  ihe  want  and  use  of  students,  a  work  rich  in  statistics— clear  in  practice— and  free  in 
siyle— possessing  no  small  claims  to  our  confidence. — The  New  York  Journal  of  Medicine. 

WILLIAMS'  PATHOLOGY. 

PRINCIPLES    OF    ME  DICINE, 

COMPttlSINO 

6ENEBAL  PATHOLOGY  AND  THERAPEUTICS, 

XVl)  A  GBNEUAL  VIEW  OF 

ETIOLOGY,  NOSOLOGY,  SEMEIOLOGY,  DIAGNOSIS  AND  PROGNOSIS. 
BY  CHARLES  J.  B.  WILLIAMS,  M.D.,  F.R.S., 

FeliOw  of  the  Royal  College  of  Physicians,  &c. 

WITH  NOTK8  AND  ADHITIONS, 

BY  MEREDITH  CLYMER,  M.  D.,  &c. 

In  one  volume,  octavo. 


PEREIRA'S    MATERIA    MEDICA. 

Willi  nearly  Three  Hundred  Engravings  on  Wood. 

A  NEW    EDITION,  LATELY  PUBLISHED. 

THE  ELEMENTS  OF 

MATERIA  MEDICA  AND  THERAPEUTICS. 

co^iphehknuing 

THE  NATURAL  HISTORY,  PREPARATION,  PROPERTIES,  COMPO- 
SITION, EFFECTS  AND  USES  OF  MEDICINES. 
BY  JONATHAN  PEREIRA,  M.D.,  F.R.S.  and  L.S. 

Member  of  the  Society  of  Pharmacy  of  Paris;  Examiner  in  Materia  Medica  and  Pharmacy  of  the  University 
of  London;  Lecturer  on  Materia  Medica  at  the  London  Hospital.  &c  Sec. 
Second  American,  from  the  last  London  Edition,  enlarged  afid  improved. 

WITH  NOTES  AND  ADDITIONS  BY  JOSEPH  CARSON,  M.D. 

In  two  volumes;  octavo,  containing  Fifteen  Hundred  very  large  pages,  illustrated  by  Two  Hundred  and 

i?eventy-five  Wood-cuts 

This  encycloprcdia  of  materia  medica,  for  such  it  may  justly  be  entitled,  gives  the  fullest  and  most  ample  ex- 
position of  materia  medica  and  its  associate  branches  of  any  work  hitherto  published  in  ihe  English  language. 
It  abounds  in  research  and  erudition:  its  statements  of  facts  are  clear  and  meiliodically  arranged,  while  its 
therapeutical  explanations  are  philosophical,  and  in  accordance  with  sound  clin:cal  experience.  It  is  equally 
adapted  as  a  text-iiook  for  students,  or  a  work  of  reference  for  the  advanced  practitioner,  and  no  one  can 
consult  its  pages  without  profit.  The  editor  has  performed  his  task  with  much  ability  and  judgment.  In  the 
first  American  edition,  he  adopted  the  PharmaeoptEia  of  the  United  Stales,  and  the  formulaj  .set  forth  in  that 
friandard  authority;  in  the  present  he  has  introduced  an  account  of  substances  that  have  recently  attracted  at- 
tention by  their  therapeutic  employment,  together  with  the  mode  of  forming  the  characters  and  uses  of  new 
pharmaceutic  preparations,  and  the  details  of  more  elaborate  and  particular  chemical  investigations,  w^ith 
respect  to  the  nature  of  previously  known  and  already  described  elementary  principles— all  the  important 
indigenous  medicines  of  the  United  States  heretofore  known  are  also  described.  The  work,  however,  is  too 
well  known  to  need  any  further  remark.  We  have  no  doubt  it  will  have  a  circulation  commensurate  with  its 
extraordinary  merits.—  The  New  York  Journal  of  Medicine. 

•'  An  Encyclopedia  of  knowledge  in  that  department  of  medical  science— by  the  common  consentofthe  pro- 
fession the  most  elaborate  and  scientific  Treatise  on  Materia  Medica  in  our  language."— Wesiern  Journal  of 
Medicine  and  Surgery. 


LEA  &  BLANCHARD'S  PUBLICATIONS.  11 

WILSON'S  ANATOMY.    New  Edition— Now  Ready,  1847. 

A   SYSTEM    OF    HUMAN   ANATOMY, 
GENERAL   AND  SPECIAL. 

BY  ERASMUS  WILSON,  M,D., 

Lecturer  on  Anatomy,  London. 
THIRD  AMERICAN  FROM  THE  LAST  LONDON  EDITION. 

EDITED  BY  P.  B.  GODDARD,  A.M.,  M.D., 

Pfofesfor  of  Anatomy  in  the  Franklin  Medical  Coljf-ge  of  Philadelpliia. 

WITH  TWO  HUNDRED  AND  THIRTY-FIVE  ILLUSTRATIONS  BY  GILBERT. 

In  one  beautiful  octavo  volume  of  over  SIX  HUJWJDREH  Iiarge  jPag-ea, 

Strongly  Bound  and  sold  at  a  low  price. 

Since  the  publication  of  the  second  American  edition  of  this  work,  the  author  has  issued  a  new 
edition  in  London,  in  which  he  has  carefully  brought  up  his  work  to  a  level  with  the  most  advanced 
science  of  the  day.  All  the  elementary  chapters  have  been  re-written,  and  such  alterations  made 
through  the  body  of  the  work,  by  the  introduction  of  all  new  facts  of  interest,  illustrated  by  appro- 
priate engravings,  as  much  increase  its  value.  The  present  edition  is  a  careful  and  exact  reprint 
of  the  English  volume,  with  the  addition  of  such  other  illustrations  as  were  deemed  necessary  to  a 
more  complete  elucidation  of  the  text;  and  the  insertion  of  such  of  the  notes  appended  to  the  last 
American  edition  as  had  not  been  adopted  by  the  author  and  embodied  in  his  text;  together  with 
such  additional  information  as  appeared  calculated  to  enhance  the  value  of  the  work.  It  may  also 
be  stated  that  the  utmost  care  has  been  taken  in  the  revision  of  the  letter-press,  and  in  obtaining 
clear  and  distinct  impressions  of  the  accompanying  cuts. 

It  will  thus  be  seen,  that  every  effort  has  been  used  to  render  this  text-book  worthy  of  a  con- 
tinuance of  the  great  favor  with  which  it  has  been  everywhere  received.  Professors  desirous  of 
adopting  it  for  their  classes  may  rely  on  being  always  able  to  procure  editions  brought  up  to  the 
day. 

This  book  is  well  known  for  the  beauty  and  accuracy  of  its  mechanical  execution.  The  present 
edition  is  an  improvement  over  the  last,  both  in  the  number  and  clearness  of  its  embellishments; 
it  is  bound  in  the  best  manner  in  strong  sheep,  and  is  sold  at  a  price  which  renders  it  accessible 
to  all. 


CONDIE  ON  CHILDREN.— New  Edition,  1847. 

A  practicaiTtreatise  on 

THE     DISEASES     OF     CHILDREN, 

BY  D.  FRANCIS  CONDIE,  M.  D, 

Fellow  of  ihe  College  of  Physicians,  Member  of  the  American  Philosophical  Society,  &c. 
In  one  large  octavo  volume. 

iHr"  The  publishers  would  particularly  call  the  attention  of  the  profession  to  an  examination  of  this  book. 

In  the  preparation  of  a  new  edition  of  the  present  treatise,  every  part  of  the  work  has  been  subjected  to  a 
careful  revision;  several  portions  have  been  entirely  rewritten;  wMiile,  throughout,  numerous  additions 
have  been  made,  comprising  all  the  more  important  facts,  in  reference  to  the  nature,  diagnosis,  and  treat- 
ment of  the  diseases  of  infancy  and  childhood,  ihat  have  been  developed  since  the  appearance  of  the  first 
edition.  It  is  wiih  some  confidence  that  the  author  presents  this  edition  as  embracing  a  full  and  connected 
view  of  the  actual  state  of  the  pathology  and  therapeutics  of  those  aifections  which  most  usually  occur  be- 
tween birth  and  puberty. 

This  work  is  being  introduced,  as  a  text-book,  very  extensively  throughout  the  Union. 


CHURCHILL  ON  FEMALES.    New  Edition,  1847.— Now  Ready. 

THE  DISEASEToF  FEMALES, 

INCLUDING  THOSE  OF  ' 

PREGNANCY  AND    CHILDBED. 

BY  FLEETWOOD   CHURCHILL,  M  D., 

Author  of  "Theory  and  Practice  of  Midwifery,"  &c.  &c. 
.  FOURTH  AMERICAN,  FROM  THE  SECOND  LONDON  EDITION,  WITH  ILLUSTRATIONS. 

EDITED,    WITH    NOTES, 
BY    ROBERT     M.      HUSTON,    M.D.,&c.&c. 

In  one  volume,  8vo. 
The  rapid  sale  of  three  editions  of  this  valuable  work,  stamp  it  so  emphatically  with  the  approbation  of  the 
profession  of  this  country,  that  the  publishers  in  presenting  a  fourth  deem  it  merely  necessary  to  observe, 
that  every  care  has  been  taken,  by  the  editor,  to  supply  any  deficiencies  which  may  have  existed  in  former 
impressions,  and  to  bring  the  work  fully  up  to  the  date  of  publication. 


12  LEA  &  BLANCHARD'S  PUBLICATIONS. 

LIBRARY  OF  OPHTHALMIC  MEDICINE  AND  SURGERY. 
Brought  up  to  1847. 

A  TREATISE  ON  THE^^ISEASES  OF  THE  EYE. 

BY    W.    LAWRENCE,    F.R.S., 

Surgeon  Extraordinary  to  the  Queen,  Surgeon  to  St.  Bartholomew's  Hospital,  &c.  &c. 
A    NEW     EDITION, 

With  many  Modifications  and  Additions,  and  the  Introduction  of  nearly  two  hundred  Illustrations. 

BY     ISAAC     HAYS,    M.  D., 

Surgeon  to  Wills'  Hospital,  Physician  to  the  Philadelphia  Orphan  Asylum,  &c.  &c. 

In  one  very  large  octavo  volume  of  near  900  pages,  with  tw^elve  plates  and  numerous  wood-cuts  through 

the  text. 

This  is  among  the  largest  and  most  complete  works  on  this  interesting  and  difficult  branch  of  Medica 
Science. 

The  early  call  for  a  new  edition  of  this  work,  confirms  the  opinion  expressed  by  the  editor  of  its  great 
value,  and  has  stimulated  him  to  renewed  exertions  to  increase  its  usefulness  to  practitioners,  by  incorporat-' 
ing  in  it  the  recent  improvements  in  Ophthalmic  Practice.  In  availing  himself,  as  he  has  freely  done,  of 
the  oi)servations  and  discoveries  of  his  fellow-laborers  in  the  same  field,  the  editor  has  endeavored  to  do  so 
with  entire  fairness,  always  awarding  to  others  what  justly  belongs  to  them.  Among  the  additions  which 
have  been  made,  may  be  noticed,— the  descriptions  of  several  afleclions  not  treated  of  in  the  original, — an 
account  of  the  catoptric  examination  of  the  eye,  and  of  its  employment  as  a  means  of  diagnosis.— one  hun- 
dred and  seventy-six  illustrations,  some  of  ihem  from  original  drawings,— and  a  very  full  index.  There  have 
also  been  introduced  in  ihe  several  chapters  on  the  more  important  diseases,  the  results  of  the  editor's  ex- 
perience in  regard  to  their  treatment,  derived  Oom  more  than  a  quarter  of  a  century's  devotion  to  the  subject, 
during  all  of  which  period  he  has  been  attached  to  some  public  institution  for  the  treatment  of  diseases  of  the 
eye. 

"  We  think  there  are  few  medical  works  which  could  be  so  generally  acceptable  as  this  one  will  be  to  the 
profession  on  this  side  of  the  Atlantic.  The  want  of  a  scientific  and  comprehensive  treatise  on  Diseases 
of  the  Eye,  has  been  much  deplored.  That  want  is  now  well  supplied.  The  reputation  of  Mr.  Lawrence 
as  an  Oculist  has  been  long  since  fully  established;  his  great  merit  consists  in  the  clearness  of  his  style 
and  the  very  practical  tenor  of  his  work.  The  value  of  tlie  present  beautiful  edition  is  greatly  enhanced, 
by  the  important  additions  made  by  the  editor.  Dr.  Hays  has,  for  nearly  a  quarter  of  a  century,  been  con- 
nected with  public  institutions  for  the  treatment  of  Diseases  of  the  Eye,  and  few  men  have  made  better  im- 
provement than  he  has.  of  such  extensive  opportunities  of  acquiring  a  thorough  knowledge  of  the  subject. 
The  wood-cuts  are  executed  with  great  accuracy  and  beauty,  and  no  man,  wlio  pretends  to  treat  diseases 
of  the  eye,  should  be  without  this  work."— I-ancef. 


JONES  ON  THE  EYE.    Now  Ready. 

THE  PRINCIPLESAND  PRACTICE 
OF  OPHTHALMIC  MEDICINE  AND  SURGERY. 

By  T.  WHARTON  JONES,  F.R.S.,  &c.  &c. 

-WITH    ONE    HUNDRED    AND    TEN    ILIiUSTRATIONS. 

EDITED  BY  ISAAC  HAYS,  M.D.,  &c. 

In  One  very  neat  Volume,  large  royal  12mo.,  idth  Four  Plates,  plain  or  colored,  and  Ninety- 
eight  well  executed  Wood-cuts. 

This  volume  will  be  found  to  occupy  a  place  hitherto  unfilled  in  this  department  ofmedical  science. 
The  aim  of  the  author  has  been  to  produce  a  work  which  should,  in  a  moderate  compass,  be  suffi- 
cient to  serve  both  as  a  convenient  text-book  for  students  and  as  a  book  of  reference  for  practitioners, 
suitable  for  those  who  do  not  desire  to  possess  the  larger  and  encyclopaBdic  treatises,  such  as 
3-..awrence's.  Thus,  by  great  attention  to  conciseness  of  expression,  a  strict  adherence  to  arrange- 
ment, and  the  aid  of  numerous  pictorial  illustrations,  he  has  been  enabled  to  embody  in  it  the  prin- 
ciples of  ophthalmic  medicine,  and  to  point  out  their  practical  application  more  fully  than  has 
Vjeen  done  in  any  other  publication  of  the  same  size.  The  execution  of  the  work  will  be  found 
to  correspond  with  its  merit.  The  illustrations  have  been  engraved  and  printed  with  care,  and  the 
whole  is  confidently  presented  as  in  every  way  worthy  the  attention  of  the  profession. 

"  We  are  confident  that  the  reader  will  find,  on  perusal,  that  the  execution  of  the  work  amply  fulfils  the 
promise  of  the  preface,  and  sustains,  in  every  point,  the  already  high  reputation  of  the  author  as  an  ophthal- 
mic surgeon,  as  well  as  a  physiologist  and  pathologist.  The  hook  is  evidently  the  result  of  much  labor  and 
research,  and  has  heen  written  with  the  greatest  care  and  attention  ;  it  possesses  that  best  quality  which  a 
general  work,  like  a  system,  or  manual,  can  show,  viz  :— the  quality  of  having  all  the  materials  whenccso- 
ever  derived,  sollioroughly  wrought  up.  and  digested  in  the  author's  mind,  as  to  come  forthwith  the  freshness 
and  impressiveness  of  an  original  production.  We  regret  that  we  have  received  the  book  at  so  late  a  period 
as  precludes  our  giving  more  than  a  mere  Tiotice  of  it,  as  although  essentially  and  necessarily  a  compilation, 
it  caivtains  many  things  which  we  should  be  glad  to  reproduce  in  our  pages,  whether  in  the  shapt;  of  new 
pathological  views,  of  old  errors  correctt'd.  or  of  sound  principles  of  practice  in  doubtful  cases  clearly  laid 
down.  But  we  dare  say  most  of  our  readers  will  shortly  have  an  opportunity  of  seeing  these  in  their  original 
locality,  as  we  entertain  little  doubt  that  this  book  will  become  what  its  author  hoped  it  might  become,  a 
manual  for  daily  reference  and  consultation  by  the  student  and  the  general  practitioner.  The  work  is 
marked  by  that  correctness,  clearness  and  precision  of  style  which  distinguish  all  the  productions  of  the 
learned  ainhoT.''— The  British  a?id  Foreign  Medical  Review. 


LEA  &  BLANCHARD'S  PUBLICATIONS.  13 

NEW  AND  COMPLETE  MEDICAL  BOTANY. 

NOW    EEADY. 

medicalIotany, 

OR,  A  DESCRIPTION  OF  ALL  THE  MORE  IMPORTANT  PLANTS  USED  IN 

MEDICINE,    AND    OF    THEIR    PROPERTIES,    USES    AND 

MODES  OF  ADMINIS  f-RATION. 

BY  R.  EGLESFELD  GRIFFITH,  M.D.,  &c.  &c. 

In  one  large  octavo  volume. 

With  about  three  hundred  and  fifty  Illustrations  on  Wood. 
Specimens  of  the  Cuts  are  annexed,  but  not  so  well  printed  as  in  the  work,  nor  on  as  good  paper. 

This  work  is  intended  to  supply  a  want  long  felt  in  this  country,  of  some  treatise  present- 
ing correct  systematic  descriptions  of  medicinal  plants,  accompanied  by  representations  of 
the  most  important  of  them,  and  furnished  at  a  price  so  moderate  as  to  render  it  generally 
accessible  and  useful.  In  the  arrangement,  the  author  has  treated  more  fully  of  those 
plants  which  are  known  to  be  of  the  greatest  importance;  and  more  especially  of  such  as 
are  of  native  origin  ;  while  others,  rarely  used,  are  briefly  noticed,  or  mentioned  only  by 
name.  In  all  cases,  the  technical  descriptions  are  drawn  up  in  accordance  with  the  existing 
.state  of  botanical  knowledge,  and  in  order  that  these  maybe  fully  appreciated,  even  by  those 
not  proficients  in  the  science,  an  Introduction  has  been  prepared,  containing  a  concise  view 
of  Vegetable  Physiology,  and  the  Anatomy  and  Chemistry  of  Plants.  Besides  this,  a  very 
copious  GLossAnx  of  botanical  terms  has  been  appended,  together  with  a  most  complete 
Index,  giving  not  only  the  scientific  but  also  the  common  names  of  the  species  noticed  in 
it.  It  will  thus  be  ?^Qen.  that  the  work  presents  a  view  not  only  of  the  properties  and  medical 
virtues  of  the  various  species  of  the  vegetable  world,  but  also  of  their  organization,  compo- 
sition and  classification. 

To  the  student,  who  is  really  anxious  to  study  Botany  for  those  great  purposes  which  ren- 
der it  so  necessary  for  the  advancement  of  Medical  Science,  and  who  has  been  obliged  to 
rest  satisfied  with  such  imperfect  knowledge  as  can  be  obtained  from  the  different  treatises 
on  the  Materia  Medica,  the  present  work  will  be  of  great  utility  as  a  text-book  and  guide  in 
his  researches,  as  it  presents  in  a  condensed  form,  all  that  is  at  present  known  respecting 
those  vegetable  substances  which  are  employed  to  alleviate  suffering  and  to  minister  to  the 
wants  of  man.  It  will  also  be  found  extremely  convenient  to  practitioners  through  the 
country,  who  are  anxious  to  obtain  a  knowledge  of  the  medicinal  plants  occurring  in  their 
vicinity,  and  who  are  unwilling  to  procure  the  scarce  and  high-priced  works  which  are  at 
present  the  only  ones  accessible  on  this  important  branch  of  medical  knowledge. 

Great  care  has  been  taken  to  render  the  mechanical  execution  satisfactory. 


NOW     PREPARING, 
AND    TO    BE    READY    BY    AUGUST    NEXT, 

AN  ANALYTICAL  COMPEND  OP  THE  YARIODS  BRANCHES  OP 

PRACTICAL  MEDICINE,  SURGERY,  ANATOMY, 

MIDWIFERY,  DISEASES  OF  WOMEN  AND  CHILDREN, 
•Jflattria  Jfledicu  and  Therapeutics^  Phifsiology^ 

By  JOHN  NEILL,  M.  D  , 

Demonstrator  of  Anatomy  in  the  University  of  Pennsylvania,  and 

F.    GURNEY    SMITH,    M.D., 

Lecturer  on  Physiology  in  the  Philadelphia  Association  for  Medical  Instruction. 
To  make  one  large  royal  Duodecimo  volume,  with  numerous  Illustrations  on  Wood. 
It  is  the  intention  of  the  publishers  to  page  this  work  in  such  a  way,  that  it  can  be  done  up  in 
separate  divisions,  and  in  paper  to  go  by  mail;  no  one  division  will  cost  over  50  cents,  thus  pre- 
senting separate  MANUALS  on  the  various  branches  of  medicine,  and  at  a  very  low  price. 


SPECIMEN  OF  THE  ILlUSTRiTIONS  IN 

GRIFFITH'S   MEDICAL   BOTANY. 


LEA  &  BLANCHARD'S  PUBLICATIONS.  15 

THE  GREAT  MEDICAL  LIBRARY. 
THE  CYCLOP/EDIA  OF  PRACTICAL  MEDICINE  j 

COMPRISING  TREATISES  ON  THE 

NATURE  AND  TREATMENT  OF  DISEASES,    ' 

MATERIA  MEDICA  AND  THERAPEUTICS, 

DISEASES  OF  WOMEN  AND  CHILDREN, 
MEDICAL  JURISPRUDENCE,  &c.  &c. 

EDITED   BY 

JOHN  FORBES,  M.  D.,  F.  R.  S., 
ALEXANDER   TWEEDIE,   M.D.,   F.R.S., 

AXD 

JOHN   CONOLLY,   M.D. 

REVISED,  WITH  ADDITIONS, 

By  ROBLEY  DUNGLISON,  M.  D. 

THIS  WORK  IS  NOW  COMPLETE,  AND  FORMS 

FOUR  LARGE  SUPER-ROYAL,  OCTAVO  VOLUMES. 

CONTAINING  THIRTY-TWO  HUNDRED  AND  FIFTY-FOUR 

UNUSUALLY  LARGE  PAGES  IN  DOUBLE  COLUMNS, 

PRINTED  ON  GOOD  PAPER,  WITH  A  NEW  AND  CLEAR  TYPE. 
THE  WHOLE  WELL  AND  STRONGLY  BOUND, 
WITH  RAISED  BANDS  AND  DOUBLE  TITLES. 
Or,  to  he  had  in  twenty-four  parts,  at  Fifty  Cents  each. 

For  a  list  of  Articles  and  Authors,  together  with  opinions  of  the  press,  see  Supplement  to  the  No- 
vember number  of  the  Medical  News  and  Library  for  1845. 

This  work  having  been  completed  and  placed  before  the  profession,  has 
been  steadily  advancing  in  favor  with  all  classes  of  physicians.  The  nu- 
merous advantages  which  it  combines,  beyond  those  of  any  other  work ;  the 
weight  which  each  article  carries  with  it,  as  being  the  production  of  some 
physician  of  acknowledged  reputation  who  has  devoted  himself  especially 
to  the  subject  confided  to  him;  the  great  diversity  of  topics  treated  of;  the 
compendiousness  with  which  everything  of  importance  is  digested  into  a 
comparatively  small  space  ;  the  manner  in  which  it  has  been  brought  up 
to  the  day,  everything  necessary  to  the  American  practitioner  having  been 
added  by  Dr.  Dunglison ;  the  neatness  of  its  mechanical  execution ;  and 
the  extremely  low  price  at  which  it  is  afforded,  combine  to  render  it  one  of 
the  most  attractive  works  now  before  the  profession.  As  a  book  for  con- 
stant and  reliable  reference,  it  presents  advantages  which  are  shared  by  no 
other  work  of  the  kind.  To  country  practitioners,  especially,  it  is  abso- 
lutely invaluable,  comprising  in  a  moderate  space,  and  trifling  cost,  the 
matter  for  which  they  would  have  to  accumulate  libraries,  w^hen  removed 
from  public  collections.  The  steady  and  increasing  demand  with  w^hich 
it  has  been  favored  since  its  completion,  shows  that  its  merits  have  been 
appreciated,  and  that  it  is  now  universally  considered  as  the 

LIBRARY  FOR  CONSULTATION  AND  REFERENCE. 


SMITH  &  HORNER'S  ANATOMICAL  ATLAS. 


W 


Just  Published,  Price  Five  Dollars  in  Parts. 


AN 

ANATOMICAL    ATLAS 
ILLUSTRATIVE  OF  THE  STBUCTnilE  OF  THE  HUMAN  BOUT. 

BY  HENRY  H.  SxMITH,  M.  D., 

Feiloio  of  the  College  of  Physicians^  ^c. 
UiN'DER  THE  SUPERVISION  OF 

WILLIAM  E.  HORNER,  M.  D., 

Professor  of  Anatomy  in  t/ie  University  of  Fetmsylvamcu  , 

In  One  large  Volume,  Imperial  Octavo. 

This  work  is  but  just  completed,  having  been  delayed  over  the  time  intended  by  the  great  difficulty  in  giving 
to  the  illustrations  the  desired  finish  and  perfection.    It  consists  of  five  pans,  whose  contents  are  as  lbllovtr«: 

Part     I.  The  Bones  and  Ligaments,  with  one  hundred  and  thirty  engravings. 

Part   II.  The  Muscular  and  Dermoid  Systems,  with  ninety-one  engravings. 

.Part  III.  The  Organs  of  Digestion  and  Generation,  with  one  hundred  and  ninety-one  engravings. 

Part  IV.  The  Organs  of  Respiration  and  Circul-alion,  with  ninety-eight  engravings. 

Part   V.  The  Nervous  System  and  the  Senses,  with  one  hundred  and  twenty-six  engravings. 
Forming  altogether  a  complete  System  of  Anatomical  Plates,  of  nearly 

SIX   HUNDRED   AND   FIFT^Y   FIGURES, 
executed  in  the  best  style  of  art,  and  making  one  iarge  imperial  octavo  volume.    Those  who  do  not  want  it  in 
parts  can  have  the  work  bound  in  extra  cloth  or  sheep  at  an  extra  cost. 

This  work  possesses  novelty  both  in  the  design  and  the  *"xecution.  It  is  the  first  attempt  to  apply  engraving 
on  wood,  on  a  large  scale,  to  the  illustration  of  human  anatomy,  and  the  beauty  of  the  parts  issued  induces  the 
publishers  to  flatter  themselves  with  the  hope  of  the  perfect  success  of  their  undertaking.  The  plan  of  the 
work  is  at  once  novel  and  convenient.  Each  page  is  perfect  in  itself,  the  references  being  immediately  untler 
the  figures,  so  that  llie  eye  takes  in  the  whole  at  a  glance,  and  obviates  the  necessity  of  continual  reference 
backwards  and  forwards.  The  cuts  are  selected  from  the  best  and  most  accurate  sources ;  and,  where  neces- 
sary, original  drawings  have  been  made  from  the  admirable  Anatomical  Collection  of  the  University  of  Penu 
gylvania.  It  embraces  all  the  late  beautiful  discoveries  arising  from  tlie  use  of  the  microscope  in  the  investi- 
gation of  the  minute  structure  of  the  tissues. 

In  the  getting  up  of  this  very  complete  work,  the  publishers  have  spared  neither  pains  nor  expense,  and  tliey 
now  present  it  to  the  protession.  with  the  full  confidence  that  it  will  Ije  deemed  all  that  is  wanted  in  a  scientific 
and  artistical  point  of  view,  while,  at  the  same  time,  its  very  low  price  places  it  within  the  reach  of  all. 

It  is  particularly  adapted  to  supply  tlu  place  ofsktktons  or  subjects,  cu  the  profession  will  see  by  examining  the  list 
of  plates 


"These  figures  are  well  selected,  and  present  a  complete  and  accurate  representationof  that  wonderful  fabric, 
the  human  body.  The  plan  of  this  Atlas,  which  renders  it  so  peculiarly  conveniejit  for  the  student,  and  its 
superb  artistical  execuiioUj  have  been  already  pointed  out.  We  must  congratulate  the  student  upon  the 
completion  of  this  atlas,  as  it  is  the  most  convenient  work  of  the  kind  that  has  yet  appeared;  and,  we  must 
add,  the  very  beautiful  manner  in  which  it  is  '  got  up'  is  so  creditable  to  the  country  us  to  be  flattering  to  our 
national  pride." — American  Medical  Journal. 

"This  is  an  exquisite  volume,  and  a  beautiful  specimen  of  art.  "We  have  numerous  Anatomical  Atlases, 
but  we  will  venture  to  say  that  none  equal  it  in  cheapness,  and  none  surjiass  it  in  faithfulness  and  spirit.  We 
strongly  recommend  to  our  tnends.  both  urban  and  suburban,  the  purrlia.se  of  this  excellent  work,  for  which 
both  editor  and  publisher  deserve  tne  thanks  of  the  profession." — Mtdical  Examiner. 

"We  would  strongly  reconnnend  it,  not  only  to  the  student,  but  also  to  the  working  practitioner,  who, 
although  grown  rusty  in  the  toils  of  his  harness  still  has  the  desire,  and  often  the  necessity,  of  refreshing  his 
knowledge  in  this  fundamental  part  of  the  science  of  medicine." — New  York  Journal  of  Medicine  and  Surg, 

"  The  plan  of  this  Atlas  is  admirable,  and  its  execution  superior  to  any  thing  of  the  kind  before  published  m 
this  country.  Il  is  a  real  labour-saving  affair,  and  we  regard  Us  publication  as  the  greatest  boon  that  could  be 
conferred  on  the  student  of  anatomy.  It  will  be  equally  valuable  to  the  practitioner,  by  alTording  him  an  easy 
means  of  recalling  the  details  learned  in  tlie  dissecting  room,  and  wiiich  are  soon  forgotten." — American  Medi- 
cal Journal. 

"  It  is  a  beautiful  as  well  as  particularly  useful  design,  which  should  be  extensively  patronized  by  physicians, 
surgeons  and  medical  siudtjnis." — Boston  Med.  and  Surg.  Journal. 

"  It  has  been  the  aim  of  the  author  of  the  Atlas  to  comprise  in  it  tne  valuable  points  of  all  previous  works,  to 
embrace  the  latest  microscopical  observations  on  the  anatomy  of  the  tissues,  and  by  placing  it  at  a  moderate 
price  to  enable  all  to  accjuire  it  who  may  need  its  assistance  in  the  dissecting  or  operating  room,  or  other  field 
of  practice." — Wenern  Journal  of  Med.  and  Surgery. 

''These  numbers  complete  the  series  of  this  beautiful  work,  which  fully  merits  the  praise  bestowed  upon  the 
earlier  numbers.  We  regard  all  the  engravings  as  possessing  an  accuracy  only  equalled  by  their  beauty, 
and  cordially  recommend  tlie  work  to  all  engaged  in  tlie  study  of  anatomy."— i\^K«>  York  Journal  of  Medicine 
atul  Surgery. 

"A  more  elegant  work  than  the  one  before  us  could  not  easily  be  placed  by  a  physician  upon  tlie  table  of 
his  student.*' — Western  Journal  of  Medicine  and  Surgery. 

"We  were  much  pleased  with  Part  I,  but  the  Second  Part  gratifies  us  still  more,  both  as  regards  the  attract- 
ive nature  of  the  subject.  (The  Dermoid  and  Muscular  Systems.)  and  the  beautiful  artistical  execution  of  the 
.Ihistrations.  We  have  here  delineated  the  most  accurate  microscopic  views  of  some  of  the  tissues,  as,  for 
instance,  the  cellular  and  adipose  tissues,  the  epidermis,  rete  mucosum  and  cutis  vera,  the  sebaceous  and 
perspiratory  organs  of  the  skin,  the  perspiratory  giauds  and  hairs  of  the  skm,  and  the  hair  and  nails.  Then 
follows  the  general  aiinloniy  of  the  muscles,  and.  lastly,  ilieir  separate  delineations.  We  would  recommend 
this  Anatomical  Atlas  to  our  readers  in  the  very  strongest  lernis." — New  York  Journal  of  Medicine  and  Sur- 
gery. 


LEA  &  BLANCHARD'S  PUBLICATIONS.  f? 

HORNER'S  ANATOMY; 

NEW  EDITION. 

SPECIAL  anatomy"  AND   HISTOLOGY. 

BY  WILLIAM  E.  HORNER,  M.D., 

PROFESSOR  OF  ASATOMT  IN  THE  UJflVEBSITI  OF  PENNSYLVANIA,  &C.,  &C. 

Seventh  edition. 

With  many  improvements  and  additions.    In  two  octavo  volumes,  with  illustrations  on 

wood. 

This  standard  work  has  been  so  long  before  the  profession,  and  has  been  so  extensively- 
used,  that,  in  announcing?  the  new  edition,  it  is  only  necessary  to  state,  that  it  has  under- 
gone a  most  careful  revision  ;  the  author  has  introduced  many  illustrations  relating  to  Mi- 
croscopical Anatomy,  and  has  added  a  large  amount  of  text  on  those  various  points  of 
investigation  that  are  rapidly  advancing  and  attracting  so  much  attention.  This  new  edition 
has  been  arranged  to  refer  conveniently  to  the  illustrations  in  Smith  and  Horner's  Anato- 
mical Atlas. 

"The  name  of  Professor  Horner  is  a  sufficient  voucher  for  the  fidelity  and  accuracy  of 
any  work  on  anatomy,  but  if  any  further  evidence  could  be  required  of  the  value  of  the  pre- 
sent publication,  it  is  afforded  by  the  fact  of  its  having  reached  a  seventh  edition.  It  is 
altogether  unnecessary  now  to  inquire  into  the  particular  merits  of  a  work  which  has  been 
so  long  before  the  profession,  and  is  so  well  known  as  the  present  one,  but  in  announcing  a 
new  edition,  it  is  proper  to  state  that  it  has  undergone  several  modifications,  and  has  been 
much  extended,  so  as  to  place  it  on  a  level  with  the  existing  advanced  state  of  anatomy. — 
The  histological  portion  has  been  remodelled  and  rewritten  since  the  last  edition;  numerous 
wood  cuts  have  been  introduced,  and  specific  references  are  made  throughout  the  work  to 
the  beautiful  figures  in  the  Anatomical  Atlas,  by  Dr.  H.  H.  Smith." — The  American  Medical, 
Journal,  for  January,  1847. 


HORNER' S^ISSECTOR. 

THE  UNITED  STATES  DISSECTOR, 

BEING  A   NEW  EDITION,  WITH  EXTENSIVE   MODIFICATIONS, 
AND  ALMOST  REWRITTEN,  OF 

'^UORJVER^S  PR^ICTIC^E,  JUVJlTO^Wir.-^^ 

IN  ONE  VERY  NEAT  VOLUME,  ROYAL  12jio. 

With  many  Illustrations  on  Wood.  "*  * 

The  numerous  alterations  and  additions  which  this  work  has  undergone,  the  improve- 
ments which  have  been  made  in  it,  and  the  numerous  wood-cuts  which  have  been  intro- 
duced, render  it  almost  a  new  work. 

It  is  the  standard  work  for  the  Students  in  the  University  of  Pennsylvania. 

Some  such  guide-book  as  the  above  is  indispensable  to  the  student  in  the  dissecting  room, 
and  this,  prepared  by  one  of  the  most  accurate  of  our  anatomists,  may  claim  to  combine  as 
many  advantages  as  any  other  extant.  It  has  been  so  favorably  received  that  the  publish- 
ers have  issued  the  fourth  edition,  which  comes  forth  embellished  by  various- wood  cuts. — 
The  copy  for  which  we  are  indebted  to  the  publishers,  although  received  by  us  a  fortnight 
since,  gives  proof  in  its  appearance  that  it  has  already  seen  service  at  the  dissecting  table, 
where  students  have  found  it  a  valuable  guide. —  The  Western  Journal  of  Medicine  and  Sur- 
gery. 


HOPE  ON  THE  HEART. 

A  TREATISE  ON  THE  DISEASES 

OF  THE  HEART  AWD  GREAT  VESSELS, 

AND  ON  THE  AFFECTIONS  WHICH  MAY  BE  MISTAKEN  FOR  THEM, 
Comprising  the  author's  view  of  the  Physiology  of  the  Heart's  Action  and  Sounds  as  demonstrated  by  his  ex- 
periments on  tlie  Motions  and  Sounds  in  1830.  and  on  ihe  Sounds  in  1834 — 5. 
BY  J.  HOPE,  M.  D.,  F.  R.  S.,  &c.  &c. 
Second  American  from  the  third  London  edition.    W^ith  Notes  and  a  Detail  of  Recent  Experiments. 
BY  C.  W.  PENNOCK,  M.  D.,  &c. 
In  one  octavo  volume  of  nearly  six  hundred  pages,  writh  lithographic  plates. 


18  LEA  &  BLANCHARD'S  PUBLICATION?. 

WORKS  BY  PROFESSOR  W.  P.  DEWEES. 

NEW    EDITIONS. 

DEWEES'S^IDWIFERY. 

A  COMPREHENSIVE  SYSTEM  OF  MIDWIFERY. 

CHIEFLY  DESIGNED    TO   FACILITATE  THE  INQUIRIES  OF  THOSE  WHO  MAY  BE  PUR- 
SUING THIS  BRANCH  OF  STUDY. 

ILLUSTRATED  BY  OCCASIONAL  CASES  AND  MANY  ENGRAVINGS. 
Eleventh  Edition,  with  the  Author^s  last  Improvements  and  Corrections. 

BY  WILLIAM  P.  DEWEES,  M.D., 

LATE  PROFESSOR  OF  MIDWIFERY  IN  THE  UNIVERSITY  OF  PENNSYLVANIA,  ETC. 
In  one  volume,  octavo, 
'  That  this  work,  notwithstanding  the  length  of  time  it  has  been  before  the  profession,  and  the  numerous  treat- 
ises that  have  appeared  since  it  was  written,  should  have  still  maintained  its  ground,  and  passed  to  edition  after 
edition,  is  sufficient  proof  that  in  it  the  practical  talt-nts  of  the  author  were  fully  placed  before  the  profes- 
sion. Of  the  book  itself  it  would  be  superfluous  to  speak,  having  been  so  long  and  so  favorably  known  through- 
out the  country  as  to  have  become  identified  with  American  Obstetrical  Science. 

DEWEES  ON  FEMALES. 

A  TREATISE  ON  THE  ISEASES  OF  FEMALES. 

BY  WILLIAM  P.  DEWEES,  M.  D.,  &c., 

LATE  PROFESSOR  OF  MIDWIFERY  IN  THE  UNIVERSITY  OF  PENNSYLVANIA,  ETC. 

EIGHTH  EDITION, 
With  the  Author's  last  Improvements  and  Corrections. 

In  one  octavo  volume^  with  plates. 

D  E  WEES    ON^lflLDR  E  N. 

A  TREATISE  ON  THE 

PHYSICAL  AND  MEDICAL  TREATMENT  OF  CHILDREN, 

BY  WILLIAM  P.  DEWEES,  M.D., 

LATE  PROFESSOR  OF  MIDWIFERY  IN  THE  UNIVERSITY  OF  PENNSYLVANIA,  ETC.  ETC. 

NINTH    EDITION. 

In  one  volume  octavo. 

This  edition  embodies  the  notes  and  additions  prepared  by  Dr.  Dewees  before  his  death,  and  will  be  found 
much  improved. 

The  objects  of  this  work  are,  1st.  to  teach  those  who  have  the  charge  of  children,  either  as  parent  or  guardian, 
the  most  approved  methods  of  securing  and  improving  their  physical  powers.  This  is  attempted  by  pointing 
out  the  duties  which  the  parent  or  the  guardian  owes  for  this  purpose,  to  this  interesting  but  helpless  class  of 
beings,  and  the  manner  by  which  their  duties  shall  be  fulfilled.  And  2d.  to  render  available  a  long  experience 
to  those  objects  of  our  affection  when  they  become  diseased.  In  attempting  this,  the  author  has  avoided  as 
much  as  possible,  "technicality,"  and  has  given,  if  he  does  not  flatter  himself  too  much  to  each  disease  of 
which  he  treats,  its  appropriate  and  designating  characters,  with  a  fidelity  that  will  prevent  any  two  being 
confounded  together,  with  the  best  mode  of  treating  them,  that  either  his  own  experience  or  that  of  others  has 
suggested. 

Physicians  cannot  too  strongly  recommend  the  use  of  this  book  in  all  families. 

ASHWELL  ON  THE  DISEASES  OF  FEMALES. 

A  PRACTICAL  TREATISE  ON  THE 

DISEASES  PECULIAR  TO  WOMEN. 

ILLUSTRATED  BY  CASES 
DERIVED    FROM    HSPOITAL    AND    PRIVATE    PRACTICE. 

By  SAMUEL  ASHWELL,  M.D., 

Member  of  the  Royal  College  of  Physicians ;  Obstetric  Physician  and  Lecturer  to  Guy's  Hospital,  &c. 

Edited  by  PAUL  BECK  GODDARD,  M.  D. 

The  whole  complete  in  one  large  octavo  volume. 
"  The  most  able,  and  certainly  the  most  standard  and  practical  work  on  female  diseases  that  we 
have  yet  seen." — Medico-Chirurgical  Review. 


LEA  &  BLANCHARD'S  PUBLICATIONS.  19 

WATSON'S  PRACTICE  OF  PHYSIC. 

NEW    EDITION    BY    CONDIE. 


LECTURES    ON    THE 

PRINCIPLES  AND  PRACTICE  OF  PHYSIC. 

DELIVERED  AT  KING'S  COLLEGE,  LONDON, 

By  THOMAS  WATSON,  M.D.,  &c.  &c. 
Second  American,  from  the  Second  Lofidon  Edition. 

REVISED,  WITH  ADDITIONS, 

BY  D.   FRANCIS  CONDIE,   M.  D., 

Author  of  a  work  on  the  "Diseases  of  Children,"  &c. 

In  One  Octavo  Volume 
Of  nearly  ELEVEN  HUNDRED  Large  Pages,  strongly  bound  with  raised  bands. 

The  rapid  sale  of  the  first  edition  of  this  work  is  an  evidence  of  its  merits,  and  of  its  general  favor  with  the 
American  practitioner.  To  commend  it  still  more  stronstly  to  the  profession,  the  publishers  have  gone  ?o  x 
great  expense  in  preparing  this  edition  with  larger  type,  finer  paper,  and  stronger  binding  with  raised  band-?. 
It  is  edited  with  reference  particularly  to  American  practice,  by  Dr.  Condie;  and  with  these  numerous  ;tii- 
provemenls,  the  price  is  still  kept  so  low  as  to  be  within  the  reach  of  all,  and  to  render  it  among  the  cheapest 
works  offered^to  the  profession.  It  has  been  received  with  the  utmost  favor  !)y  the  medical  press,  both  o'"  lii  ■* 
country  and  of  England,  a  few  of  the  notices  of  which,  together  with  a  letter  from  Professor  Chapman,  are 
submitted. 

Philadelphia,  September  Ttth,  1844. 
Watson's  Practice  of  Physic,  in  my  opinion,  is  among  the  most  comprehen- 
sive works  on  the  subject  extant,  replete  with  curious  and  important  matter,  and 
written  with  great  perspicuity  and  felicity  of  manner.  As  calculated  to  do  much 
good,  I  cordially  recommend  it  to  that  portion  of  the  profession  in  this  country 
who  may  be  influenced  by  my  judgment. 

N.  CHAPMAN,  M.D., 

Professor  of  the  Practice  and  Theory  of  Medicine  in  the  University  of  Pennsylvania. 

"We  know  of  no  work  better  calculated  for  being  placed  in  the  hands  of  the  student,  and  for  a  text-book,  and 
as  such  we  are  sure  it  will  be  very  extensively  adopted.  On  every  important  point  the  author  seems  to  have 
posted  up  his  knowledge  to  the  day." — American  MedicalJournal. 

One  of  the  most  practically  usetul  books  that  ever  was  presented  to  the  student — indeed  a  more  admirable 
summary  of  general  and  special  pathology,  and  of  the  application  of  therapeutics  to  diseases,  we  are  free  to 
say  has  not  appeared  for  very  many  years.  The  lecturer  proceeds  through  the  whole  classification  of  human 
ills,  a  capile  ad  calcem.  showing  at  every  step  an  extensive  knowledge  of  his  subject,  with  the  ability  of  commu- 
nicating his  precise  ideas  in  a  style  remarkable  for  its  clearness  and  simplicity." — N.  Y.  Journal  of  Medi- 
cine and  Surgery. 

"  We  are  free  to  state  that  a  careful  examination  of  this  volume  has  satisfied  us  that  it  merits  all  the  com- 
mendation bestowed  on  it  in  this  country  and  at  home.  It  is  a  work  adapted  to  the  wants  of  young  practi- 
tioners, combining  as  it  does,  sound  principles  and  substantial  practice.  It  is  not  too  much  to  say  that  it  is  a 
representative  of  the  actual  slate  of  medicine  as  taught  and  practised  by  the  most  eminent  physicians  of  the 
present  day,  and  as  such  we  would  advise  everyone  about  embarking  in  the  practice  of  physic  to  provide  him- 
self with  a  copy  of  iV^— Western  Journal  of  Medicine  and  Surgery. 


VdCEUS   PATHOLOGICAL  ANATOMY. 

THE 

PATHOLOGICAL  ANATOMY  OF  THE  HUMAN  BODY. 

By  JULIUS  VOGEL,  M.D.,  &c. 

TRANSLATED  FROM  THE  GERMAN,  WITH  ADDITIONS, 

By  GEORGE  E.  DAY,  M.D.,  &c. 

KUustwteti  t)»  uplnavtis  of  ©ae  ?QimtJre"li  IJlafn  anli  ©oloreti  Hnflrabfng.?. 

In  One  neat  Octavo  Volume. 

In  our  last  number  we  gave  a  pretty  full  analysis  of  the  original  of  this  very  valuable  work,  to  which  we 
must  refer  the  reader.  We  have  only  to  add  here  our  opinion  that  the  translator  has  performed  his  task  in  an 
excellent  manner,  and  has  enriched  the  work  with  many  valuable  additions.— TAe  British  and  Foreign  Medical 
Review. 

It  is  decidedly  the  best  work  on  the  subject  of  which  it  treats  in  the  English  language,  and  Dr.  Day,  whose 
translation  is  well  executed,  has  enhanced  its  value  by  a  judicious  selection  of  the  most  important  figures  from 
the  atlas,  which  are  neatly  engraved.— TAe  London  Medical  Gazette. 


m  LE\  &  BLANCHARD'S  PUBLICATIONS. 

A  NEW  EDITION  OF  THE  GREAT 

M  E  D  I  a  A  L_L  E  Z I  O  0  IT . 

A   Dictionary  of 

MEDICAL     SCIENCE, 

CONTAINING  A  CONCISE  ACCOUNT   OF  THE  VARIOUS  SUBJECTS  AND  TERMS;   WITH  THE 
FRENCH    AND   OTHER  SYNONVMES;    NOTICES  OF  CLIMATES  AND  OF  CELE- 
BRATED MINERAL  WATERS;  FORMULAE  FOR  VARIOUS  OFFICINAL 
AND  EMPIRICAL  PREPARATIONS,  &c. 

BY  HOBLEY  DUNGLISON,  M.  D., 

PROFESSOR  OF  THE  INSTITUTES  OF  MEDICINE,  ETC.  IN  JEFFERSON  MEDICAL  COLLEGE,  PHILADELPHIA. 

Sixth  edition,  revised  and  greatly  enlarged.  In  one  royal  octavo  volume  of  over  800  very  large  pages, 
double  columns.    Strongly  bound  in  the  best  leather,  raised  bands. 

"The  most  complete  medical  dictionary  in  the  English  language."—  Wtstern  Lancet. 

"  We  think  that  -the  author's  anxious  wish  to  render  the  work  a  satisfactory  and  desirable— if  not  indispen- 
sable—Lexicon, in  which  the  student  may  search  without  disappointment  for  every  term  that  has  been 
legitimated  in  the  nomenclature  of  the  science,'  has  been  fully  accomplis-hed.  Such  a  work  is  much  needed 
by  all  medical  students  and  young  physicians,  and  will  doubtless  continue  in  extensive  demand.  It  is  a 
lasting  monument  of  the  industry  and  literary  attainments  of  the  author,  who  has  long  occupied  the  highest 
rank  among  the  medical  teachers  of  America  "—TAe  New  Orleans  Medical  and  Svrgkal  Journal 

"  The  sinriple  announcement  of  the  fact  that  Dr.  Dunglison's  Dictionary  has  reached  a  sixth  edition,  is  almost 
as  high  praise  as  could  be  bestowed  upon  it  by  an  elaborate  notice.  It  is  one  of  those  standard  works  that  have 
been  '  weighed  in  the  balance  and  (not)  been  found  wanting  '  It  has  stood  the  test  of  experience,  and  the  fre- 
quent calls  for  new  editions,  prove  conclusively  that  it  is  held  by  the  profession  and  by  students  in  the  highest 
estimation.  The  present  edition  is  not  a  mere  reprint  of  former  ones;  the  author  has  for  some  time  been 
laboriously  engaged  in  revising  and  making  such  alterations  and  additions  as  are  required  by  the  rapid  pro- 
gress of  our  science,  and  the  introduction  of  new  terms  mto  our  vocabulary.  In  proof  of  this  it  is  stated  '  that 
the  present  edition  comprises  nearly  two  thousand  five  hundred  subjects  and  terms  not  contained  in  the  last. 
Many  of  these  had  been  introduced  into  medical  terminology  in  consequence  of  the  progress  of  the  science, 
and  others  had  escaped  notice  in  previous  revisions.'  We  think  that  the  earnest  wish  of  the  author  has  been 
accomplished  ;  and  that  he  has  succeeded  in  rendering  the  work 'a  satisfactory  and  desirable— if  not  indis- 
pensal)le— Lexicon,  in  which  the  student  may  search,  without  disappointment,  for  every  term  that  has  been 
legitimated  in  the  nomenclature  of  the  science.'  This  desideratum  he  has  been  enabled  to  attempt  in  suc- 
cessive editions,  by  reason  of  the  work  not  being  stereotyped  ;  and  the  present  edition  certainly  offers  stronger 
claims  to  the  attention  of  the  practitioner  and  student,  than  any  of  its  predecessors.  The  work  is  got  i\p  in 
the  usual  good  taste  of  the  publishers,  and  we  recommend  it  in  full  confidence  to  all  who  have  not  yet  supplied 
themselves  with  so  indispensable  an  addition  to  their  libraries  "—TVi*  New  York  Journal  of  Medicine. 

A  NEW  EDITION  OF  DUNGLISON'S  HDMAN  PHYSIOLOGY. 

HUMAN  PHYSIOLOGY, 

WITH  THREE  HUNDRED  AND  SEVENTY  ILLUSTRATIONS. 
BY  ROBLEY  DUNGLISON,  M.D., 

PKOFESSOR  OF  THE  INSTITUTES  OF  MEDICINE  IN  THE  JEFFERSON  MEDICAL  COLLEGE,  PHILADELPHIA,  ETC., ETC. 

Sixth  edition,  greatly  improved. — In  two  large  octavo  volumes,  containing  nearly  1350  pages. 
"  It  is  but  necessary  for  the  Author  to  say,  that  all  the  cares  that  were  bestowed  on  the  preparation  of  the 
fit'th  edition  have  been  extended  to  the  sixth,  and  even  to  a  greater  amount.  Nothing  of  importance  thai  has 
been  recorded  since  its  publication,  has,  he  believes,  escaped  his  aitniiitioa.  Upwards  of  seventy  illustrations 
have  been  added ;  and  many  of  the  former  cuts  have  been  replaced  by  others.  The  work,  he  trusts,  will  be 
found  entirely  on  a  level  with  the  existing  advanced  state  of  physiological  science." 

In  mechanical  and  artistical  execution,  this  edition  is  far  in  advance  of  any  former  one. 
The  illustrations  have  been  subjected  to  a  thorough  revision,  many  have  been  rejected  and 
their  places  supplied  wilh  superior  ones,  while  numerous  new  wood-cuts  have  been  added 
■wherever  perspicuity  or  novelty  seemed  to  require  them. 

,  "Those  who  have  been  accustomed  to  consult  the  former  editions  of  this  work,  know  with  how  much 
care  and  accuracy  every  fact  and  opinion  of  weight,  on  the  various  subjects  embraced  in  a  treatise  on 
Physiology,  are  collected  and  arranged,  so  as  to  present  the  latest  and  best  account  of  the  science  To  such 
■we  need  hardly  say,  that,  in  this  respect,  the  present  edition  is  not  less  distinguished  than  those  which  have 
preceded  it.  In  the  two  years  and  a  half  which  have  elapsed  since  the  last  or  fifih  edition  appeared,  nothing 
of  consequence  that  has  been  recorded  seems  to  have  been  omitted.  Upwards  of  seventy  illustrations  have 
been  added,  and  many  of  the  former  cuts  have  been  replaced  by  others  of  better  execution.  These  mostly 
represent  the  minute  structures  as  seen  through  the  microscope,  and  are  necessary  for  a  proper  comprehension 
of  the  modern  discoveries  m  this  department  " — The  Medical  Examiner. 

The  "  Human  Physiology"  of  Professor  Dunglison  has  long  since  taken  rank  as  one  of  the  medical  classics 
in  our  language.  Edition  after  edition  has  been  issued,  each  more  perfect  than  the  last,  till  now  we  have  the 
sixth,  with  upwards  of  seventy  new  illustrations.  To  say  that  it  is  by  far  the  best  text-book  of  physiology  ever 
published  in  this  country,  is  but  echoing  the  general  voice  of  the  profession.  It  is  simple  and  concise  in  style, 
clear  in  illustration,  and  altogether  on  a  level  with  the  existing  advanced  state  of  physiological  science.  The 
additions  to  the  present  edition  are  extremely  numerous  and  valuable;  scarcely  a  fact  worth  naming  which 
has  a  bearing  upon  the  subject  seems  to  have  been  omitted.  All  the  recent  writers  on  physiology,  both  in  the 
French,  German  and  English  languages,  have  been  consulted  and  freely  used,  and  the  facts  lately  revealed 
through  the  agency  of  organic  chemistry  and  the  microscope  have  received  a  due  share  of  attention.  As  it  is, 
w^e  cordially  recommend  the  work  as  in  the  highest  degree  indispensable  both  to  students  and  practitioners 
of  medicine. — New  York  Journal  of  Medicine. 

The  most  full  and  complete  system  of  physiology  in  our  language.— ires/ern.  Lancet. 


LEA  &  BLANCHARD'S  PUBLICATIONS.  21 

DUNGLISON'S  THERAPEUTICS. 

NEW  AND  MUCH   IMPROVED   EDITION. 

GENERAL  THERAPEUTICS  AND  MATERIA  MEDICA. 

With  One  Hundred  and  Twenty  Illustrations. 

ADAPTED  FOR  A  MEDICAL  TEXT-BOOK. 

BY  ROBLEY  DUNGLISON,  M.D., 

Professor  of  Institutes  of  Medicine,  &c.  in  Jeflerson  Medical  College;  Late  Professor  of  Materia  Medica,  &c. 
in  the  Universities  ot  Virginia  and  Maryland,  and  in  Jefferson  Medical  College. 

Third  Edition,  Revised  and  Improved,  in  two  octavo  volumes,  well  hound. 

In  this  edition  much  improvement  will  be  found  over  the  former  ones  The  author  has  subjected  it  to  a  tho- 
rough revision,  and  has  endeavored  to  so  modify  the  work  as  lo  make  it  a  more  complete  and  exact  exponent 
of  the  present  state  of  knowledge  on  the  important  subjects  of  which  it  treats.  Thefavor  with  which  the  former 
editions  were  received,  demanded  that  the  present  should  be  rendered  still  more  worthy  of  the  patronage  of  the 
profession,  and  this  alteration  will  be  found  not  only  in  the  matter  of  the  volumes,  but  also  in  the  numerous 
illustrations  introduced  and  the  general  improvement  in  the  appearance  of  the  work. 

•'This  is  a  revised  and  improved  edition  of  the  author's  celebrated  book,  entitled  '  General  Therapeutics;'  an 
account  of  the  different  articles  of  the  Materia  Medica  having  been  incorporated  with  it.  The  work  has,  in 
fact,  been  entirely  remodelled,  so  that  it  is  now  the  most  complete  and  satisfactory  exponent  of  the  existingstate 
of  Therapeutical  Science,  within  the  moderate  limits  of  a  texi-book,of  any  hitherto  published.  What  gives  the 
work  a  superior  value,  in  our  judgment,  is  the  happy  blendingof  Therapeutics  and  Materia  Medica  as  they  are, 
or  ought  lo  be  taught  in  all  our  medical  schools;  going  no  farther  into  the  nature  and  lommercial  history  of 
drugs,  than  is  indisp^isable  for  the  medical  student.  This  gives  to  the  treatise  a  clinical  and  practical  charac- 
ter, calculated  to  benefit  in  the  highest  degree,  both  students  and  practitioners.  We  shall  adopt  it  as  a  text- 
book for  our  classes,  while  pursuing  this  branch  of  medicine,  and  shall  be  happy  to  learn  that  it  has  been 
adopted  as  such,  in  all  of  our  medical  institutions  " — The  N.  Y.  Journal  of  Metiicine. 

•'Our  junior  brethren  in  America  will  find  in  these  volumes  of  Professor  Dunglison,a  'Thesaurus  Medica- 
MlNUMj'more  valuable  than  a  large  purse  of  gold."— Z-owr^on  Medico-Chiriirgical  Review. 

DUNGLISON  ON  NEW  REMEDIES. 

NEW   EDITION,   BROUGHT   UP  TO  OCTOBER  1846. 

NEW    REMEDIES. 

BY  ROBLEY  DUNGLISON,   M.D.,  &c.  &c. 

Fifth  edition,  with  extensive  additions.     In  one  neat  octavo  volume. 

The  numerous  valuable  therapeutical  agents  which  have  of  late  years  been  introduced  into  the  Matera 
Medica,  render  it  a  difficult  matter  for  the  practitioner  to  keep  up  with  the  advancement  of  the  science,  espe- 
cially a.s  the  descriptions  of  them  are  difficult  of  access,  being  scattered  so  widely  thiougli  transactions  of 
learned  societies,  journals,  monographs,  &c.  &c.  To  obviate  this  difficulty,  and  to  place  within  reach  of  the 
profession  this  important  information  in  a  compendious  form,  is  the  object  of  the  present  volume,  and  the  num- 
ber of  editions  through  which  it  has  passed  show  that  its  utility  has  not  been  underrated. 

The  author  has  taken  particular  care  that  this  edition  shall  be  completely  brought  up  to  the  present  day  — 
The  therapeutical  agents  added,  which  may  be  regarded  as  newly  introduced  into  the  Materia  Medica,  to- 
gether with  old  agents  brought  forward  with  novel  applications,  and  which  may  therefore  be  esteemed  as 
'•New  Remedies,"  are  the  following:— Benzoic  Acid.  t;hromic  Acid,  Gallic  Acid.  Nitric  Acid,  Phosphate  of 
Ammonia,  Binelli  Water,  Brocchieri  Water,  Atropia  Beerberia.  Chloride  of  Carbon  (Chloroform),  Digitalia, 
Electro-Magnetism.  Ergotin,  Oy-gall,  Glycerin,  llajmospasy.  Hacmostasis,  Hagcnia  Abyssinica.  Honey  Bee, 
Protochloride  of  Mercury  and  Quinia.  Io<loform,  Carbonate  of  liiihia,  Sulphate  of  Manganese,  Matico,  DouMe 
Iodide  of  Mercury  and  Morphia,  lodhydrate  of  Morphia,  Iodide  of  lodhydrate  of  Morphia,  Muriate  of  Mor- 
phia and  Codeia,  Naphthalin,  Piscidia  Erythritia,  Chloride  of  Lead.  Nitrate  of  Polassa,  Arseniateof  Quinia, 
Iodide  of  Quinia,  Iodide  of  Cinchonia.  Iodide  of  lodhydrate  of  Quinia,  Lactate  of  Quinia,  Pyroacetic  Acid, 
(Naphtha,  Acetone)  Hyjiosulphate  of  Soda,  Phosphate  of  Soda,  Iodide  of  lodhydrate  of  fcirychnia,  Double  Iodide 
of  Zinc  and  Strychnia,  Double  Iodide  of  Zinc  and  Morphia,  and  Valerianate  of  Zinc. 

( .''•  A  work  like  this  is  obviously  not  suitable  for  either  critical  or  analytical  review.  It  is,  so  far  as  it  goes,  a 
dispensatory,  in  which  an  account  is  given  of  the  chemical  and  physical  properties  of  all  the  articles  recenliy 
added  to  the  Materia  Medicaand  their  preparations,  with  a  noticeof  the  diseases  for  which  they  are  prescribed, 
the  doses,  mode  of  administration  &c  " — The  Medical  Examiner. 


THE    MEDIGAL    STUDENT| 

OR  AIDS  TO  THE  STUDY  OF  MEDICINE. 

A  REVISED  AXD  MODIFIED  EDITION. 

BY    ROBLEY    DUNGLISON,    M.  D. 

In  one  neat  12mo.  volume. 


HUMAN    HEALTH: 

OR,  THE   INFLUENCE   OF   ATMOSPHERE  AND  LOCALITY.  CHANGE  OF  AIR  AND  CLIMATE) 

SEASONS,   FOOD.  CLOTHir^G,  BATHIiVG    AND  MINERAL  ^PRfNGS,  EXERCISE, 

SLEEP,  CORPOREAL  AND  INTELLECTUAL  PURSUITS.  &c.  &c., 

ON  HEALTHY  MAN:  CONSTITUTING 

ELEMENTS    OF    HYGIENE. 

BY  ROBLEY  DUNGLISON,  M.  D. 

A  New  Edition  with  many  Modifications  and  Additions.    In  one  Volume,  8vo. 


«2  LEA  &  BLANCHARD'S   PUBLICATIONS. 

AMERICAN    PRACTICE    OF    MEDICINE. 

BY     PROFESSOR     DUNGLISON. 

SECOND    EDITION,    MUCH    IMPROVED.  'jlt^iji- 

THE  PRACTICE  OF  MEDICINE; 

A    TREATISE     ON 

SPECIAL    PATHOLOGY    AND    THERAPEUTICS. 

SECOND  EDITION, 

By  ROBLEY  DUNGLISON,  M.  D. 

Professor  of  the  Institutes  of  Medicine  in  the  Jefferson  Medical  College;  Lecturer  on  Clinical  Medicine.,  S^'C 

In  Two  large  Octavo  Volumes  of  over  Thirteen  Hundred  Pages. 

The  Publishers  annex  a  condensed  statement  of  the  Contents: 
Diseases  ef  the  Mouth,  Tongue,  Teeth,  Gums,  Velum  Palati  and  Uvula,  Pharynx  and 
(Esophagus,  Stomach,  Intestines,  Peritoneum,  Morbid  Productions  in  the  Peritoneum  and 
Intestines — Diseases  of  the  Larynx  and  Trachea,  Bronchia  and  Lungs,  Pleura,  Asphyxia, 
Morbid  Conditions  of  the  Blood,  Diseases  of  the  Heart  and  Membranes,  Arteries,  Veins, 
Intermediate  or  Capillary  Vessels. — Spleen,  Thyroid  Gland,  Thymus  Gland  and  Supra 
Renal  Capsules,  Mesenteric  Glands.— Salivary  Glands,  Pancreas,  Biliary  Apparatus,  Kidney, 
Ureter,  Urinary  Bladder. — Diseases  of  the  Skin,  Exanthematous,  Vesicular,  Bullar,  Pustular, 
Papular,  Squamous,  Tuberculous,  Maculae,  Syphilides. — Organic  Diseases  of  the  Nervous 
Centres,  Neuroses,  Nerves. — Diseases  of  the  Eye,  Ear,  Nose. — Diseases  of  the  Male  and 
Female  Organs  of  Reproduction. — Fever. — Intermittent,  Remittent,  Continued,  Eruptive, 
Arthritic,  Cachectic,  Scrofulous,  Scorbutic,  Chlorotic,  Rhachitic,  Hydropic  and  Cancerous. 

Notwithstanding  the  numerous  and  attractive  works  wliich  have  of  late  been  issued  on  the  Practice  of 
Physic,  these  volumes  keep  their  place  as  a  standard  text-book  for  tlie  student,  and  manual  of  reference  for 
the  practitioner.  The  care  with  which  the  author  embodies  everythinsf  of  value  from  all  sources,  the  industry 
with  which  all  discoveries  of  interest  or  importance  are  summed  up  in  succeeding  editions,  the  excellent 
order  and  system  which  is  everywhere  manifested,  and  the  clear  and  intelligible  style  in  which  his  thoughts 
are  presented,  render  his  works  universal  favorites  with  the  profession. 

'•In  the  volumes  before  us,  Dr.  Dunglison  has  proved  that  his  acquaintance  with  the  present  facts  and 
doctrines,  wheresoever  originating,  is  most  extensive  and  intimate,  and  the  judgment,  skill,  and  impartiality 
with  which  the  materials  of  the  work  have  been  collected,  weighed,  arranged,  and  exposed,  are  strikingly 
manifested  iii  every  chapter.  Great  care  is  everywhere  taken  to  indicate  the  source  of  information,  and 
under  the  head  of  treatment,  formulae  of  the  most  appropriate  remedies  are  everywhere  introduced.  In  con- 
clusion, we  congratulate  the  students  and  junior  practitioners  of  America  on  possessing  in  the  present 
volumes  a  work  of  standard  merit,  to  which  they  may  confidently  refer  in»  their  doubts  and  dilllculties." — 
Brit,  and  For.  Med.  Rev. 

''  Since  the  foregoing  observations  were  written,  we  have  received  a  second  edition  of  Dunglison's  work, 
a  suiTicient  indication  of  the  high  character  it  has  already  attained  in  America,  and  justly  attained."— I6t<f. 

"In  the  short  space  of  two  years,  a  second  edition  of  Dr.  Dunglison's  Treatise  on  Special  Pathology  and 
Therapeutics  has  been  called  for,  and  is  now  before  the  public  in  the  neat  and  tasteful  dress  in  which  Lea 
&  Blanchard  issue  all  their  valuable  publications.  We  do  not  notice  the  fact  for  the  purpose  of  passing  any 
studied  eulogy  upon  this  work,  which  is  now  too  well  known  to  the  profession  to  need  the  commendation  of 
the  press.  \ 

"A  cursory  examination  will  satisfy  any  one,  that  great  labor  has  been  bestowed  upon  these  volumes, 
and  on  a  careful  perusal  it  will  be  seen  that  they  exhibit  the  present  state  of  our  knowledge  relative  to 
special  pathology  and  therapeutics.  The  work  is  justly  a  great  favorite  with  students  of  medicine,  whose 
exigencies  the  learned  author  seems  especially  to  have  consulted  in  its  preparation."— Western  Jour,  of 
Med.  and  Surg. 

'■  This  is  a  work  which  must  at  once  demand  a  respectful  consideration  from  the  profession,  emanating  as 
It  does  from  one  of  the  most  learned  and  indefatigable  physicians  of  our  country. 

"This  arrangement  will  recommend  itself  to  the  favorable  consideration  of  all,  for  simplicity  and  com- 
prehensiveness. We  have  no  space  to  go  into  details,  and,  therefore,  conclude  by  saying,  that  although 
isolated  defects  might  be  pointed  out,  yet  as  a  whole,  we  cheerfully  recommend  it  to  the  profession,  as 
embracing  much  important  matter  which  cannot  easily  be  obtained  from  any  other  source."—  Western  Lancet. 


Hasse's  Pathological  Anatomy. 

AN  ANATOMICAL  DESCRIPTION  OF  THE  DISEASES  OF  THE 
ORGANS  OP  GXROULATIOir  AlffD  RESPIRATION. 

BY  CHARLES  EWALD  HASSE, 
Professor  of  Pathology  and  Clinical  Medicine  in  the  University  of  Zurich.,  SfC. 

Translated  and  edited  by  W,  E.  Swaine,  M.  D.,  &c. 
lu  one  octavo  volume.    A  new  work,  just  ready— October,  1846. 


LEA   &  BLANCHARD'S  PUBLICATIONS.  23 

BRODIE'S   SURGICAL  WORKS. 


CLINICAL  LECTUHES  ON  SUR6ERY| 

DELIVERED   AT    ST.   GEORGE'S   HOSPITAL 

By  Sir  BENJAMIN  BRODIE,  Bart.,  V.  P.  R.  S., 

SERJEANT  SURGEON  TO  THE  QUEEN,  ETC.  ETC. 

^  IN  ONE  NEAT  OCTAVO  VOLUME. 

"  It  would  not  be  easy  to  find  in  the  same  compass  more  useful  matter  than  is  embraced  in  each 
of  these  discourses,  or  indeed  in  this  volume.  We  the  less  regret  the  limited  extracts  we  have  it 
in  our  power  to  make  from  it,  because  we  feel  sure  that  it  will  in  a  short  time  find  its  wiy  into  ali 
the  medical  libraries  in  the  country." — The  Western  Journal  of  Medicine  and  Surgery. 

'        LECTURES 
ON  THE  DISEASES   OF   THE  URINARY  ORGANS. 

SECOND  AMERICAN  FROM  THE  THIRD  LONDON  EDITION. 

WITH  ALTERATIONS  AND  ABBITIONS. 

In  One  Small  Octavo  Volume^  Cloth. 

This  work  has  been  entirely  revised  throughout,  some  of  the  author's  views  have  been  modified, 
and  a  considerable  proportion  of  new  matter  has  been  added,  among  which  is  a  lecture  on  the 
Operation  of  Lithotomy. 

PATHOLOGICAL  AND  SURGICAL  OBSERVATIONS 
FROM  THE  FOURTH  LONDON  EDITION. 

tDitI)  tl)c  ^uti)or's  Alterations  anb  Ambitions. 

In  One  Small  Octavo  Volume,  Cloth. 

"To  both  the  practical  physician  and  the  student,  then,  this  little  volume  will  be  one  of  much  service,  ina?- 
much  as  we  have  here  a  condensed  view  of  these  complicated  subjects  thoroughly  investigated  by  the  aid  of 
the  light  affordeil  hy  modern  Pathological  Surgery."— JV.  Y.  Journal  of  Medicine. 

^[Cr'  These  three  works  can  be  had  bound  together,  forming  a  large  volume  of 
BRODIE'S  SURGICAL  WORKS. 


MILLER'S   SURGICAL  WORKS 


THE  PRINCIPLES  OF  SURGERY. 

BY  JAMES  MILLER,  F.R.S.E.,  F.R.  C.S.E., 

Professor  of  Surgery  in  the  University  of  Edinburg,  &c. 
In  one  neat  octavo  volume,  to  match  the  Author^s  volume  on  "  Practice.^^ 
"  We  feel  no  hesitation  in  expressing  our  opinion  that  it  presents  the  philosophy  of  the  science 
more  fully  and  clearly  than  any  other  work  in  the  language  with  which  we  are  acquainted." — Phi' 
ladelphia  Medical  Examiner. 

LATELY    PUBLISHED. 

THE  PRACTICK  OF  SURGERY. 

BY  JAMES  MILLER, 

Professor  of  Surgery  in  the  University  of  Edinburg. 
In  one  neat  octavo  volume. 
This  work  is  printed  and  bound  to  match  the  "  Principles  of  Surgery,"  by  Professor  Miller,  lately 
issued  by  L.  &  B.     Either  volume  may  be  had  separately. 
"  This  work,  with  the  preceding  one,  forms  a  complete  text-book  of  surgery,  and  has  been  under- 
taken  by  the  author  at  the  request  of  his   pupils.     Although  as  we  are  modestly  informed  in  the 
preface,  it  is  not  put  forth  in  rivalry  of  the  excellent  works  on  practical  surgery  which  already  exist, 
we  think  we  may  take  upon   ourselves  to   say ,that  it  will  form  a  very  successful    and  formidable 
rival  to  most  of  them.     While  it  does  not  offer  the  same  attractive  illustrations,  with  which  some  of 
our  recent  text-books  have  been  embellished,  and  while  it  will  not,  as  indeed  is  not  its  design,  set 
aside  the  more  complete  and  elaborate  works  of  reference  which  the  profession  is  in  possession  of, 
we  have  no  hesitation  in  stating  that  the  two  volumes  form,  together,  a  more  complete  text-book 
of  surgery  than  any  one  that  has  been  heretofore  offered  to  the  student." — The  Northern  Journal 
of  Medicine. 


LEA  &   BLANCHARD'S  PUBLICATIONS. 


CAB.P£:NT22B.'S  INTSW  "^OHK. 


A  MANUAL,  OR  ELEMENTS   OF  PHYSIOLOGY, 

FOU  THE  USE  OF  THE  MEDICAL  STUDENT. 

BY  WILLIAM  B.  CARPEiNTER,  M.  D.,  F.  R.  S  , 

FULLBRIAN  PKOFESSOK  OF  PHYSIOLOGY  IN  THE  ROYAL  INSTITUTION  OF  GREAT  BRITAIN,  ETC. 

With  one  hundred  and  eighty  illustrations.  In  one  octavo  volume  of  5(56  pages.  Elegantly  printed  to  match 
his  "  Principles  of  Human  Physiology." 

This  work,  though  but  a  very  short  time  published,  has  atlracled  much  attention  from  all  engaged  in  teach- 
ing the  science  of  medicine,  and  has  been  adopted  as  a  text-book  l<y  many  schools  throughout  llie  country. — 
The  clearness  and  conciseness  with  vvhich  all  the  latest  investigations  are  enunciated  render  it  peculiarly 
>veil  suited  for  those  commencing  the  study  of  medicine.  It  is  proi'usely  illustrated  with  beautiful  wood  en- 
gravings, and  is  confidently  presented  as  among  the  best  elementary  lexi-books  on  Physiology  in  the  lan- 
guage. 

The  merits  of  this  work  are  of  so  high  an  order,  and  its  arrangement  and  discussion  of  subjects  so  admi- 
rably adapted  to  the  wants  of  students,  that  we  unhesitatingly  connmend  it  io  ther  favorahle  notice.  This 
work  studied  first,  and  thoi  followed  by  the  more  elaborate  treatise  of  Dunglison.  or  Muller,  or  others  of  similar 
character,  is  decidedly  the  best  course  forthe  student  of  physiology.— TAe  Western  Lancet. 


CARPENTER'S  HUMAN  PHYSIOLOGY. 

PRINCIPLES  OF  HUMAN  PHYSIOLOGY, 

WITH  THEIR  CHIEF  APPLICAriONS  TO 

PATHOLOGY,    HYGIENE,   AND    FORENSIC    MEDICINE. 

BY  WILLIAM  B.  CARPENTER,  M.  D.,  F.  R.  S.,  &c. 

Second  American,  from  a  New  and  Revised  London  Edition. 

WITH  NOTES  AND  ADDITIONS, 

BY  MEREDITH  CLYMER,  M.  D.,  &c. 

WUh  Two  Hundred  and  Sixteen   Wood-cuts  and  other  Illu»tratton», 

In  one  octavo  volume,  of  about  650  closely  and  beautifully  printed  pages. 

The  very  rapid  sale  of  a  large  impression  of  the  firtil  edition  is  an  evidence  of  the  merits  of  this  valuable 
•work  and  that  it  has  been  duly  appreciated  by  the  profession  of  this  country  The  publishers  hope  that  the 
present  edition  will  be  found  still  more  worthy  of  approbation,  not  only  from  the  additions  of  the  author  and 
editor,  but  also  from  its  superior  execution,  and  the  abundance  of  its  illustrations.  i\o  less  than  eighty-five 
wood-cuis  and  anotner  lithographic  plate  will  be  found  to  have  been  added,  affording  the  most  material  assist- 
ance to  the  student. 

''  We  have  much  satisfaction  in  declaring  our  opinion  that  this  work  is  the  best  systematic  tr^^atise  on  pliy- 
siology  in  our  own  language,  and  the  best  adapted  for  the  student  existing  in  any  language."— iVIed/co-CAtrMrgt- 
cal  Review  of  London. 

''The  work  as  it  now  stands  is  the  only  Treatise  on  Physiology  in  the  English  language  which  exhibits  a 
clear  and  connt-cted,  and  comprehensive  view  of  the  present  condition  of  that  science."— JLo/xdon  and  Edin- 
burgh Monthly  Journal. 


SUPPLEMENT  TO  THE  ENCYCLOPJIDU  AMERICANA,  UP  TO  THE  YEAR  1847. 

ENCYCLOPiEDIA  AMERICANA-Supplementary  Vol. 

A  POPULAR  DICTIONARY 

OF  ARTS,  SCIENCES,  LITERATURE,  HISTORY,  POLITICS  AND 

BIOGRAPHY. 

VOL.    XIV. 

Edited  by  HENRY  VETHAKE,  LL.D., 

Vice-Provost  and  Professor  of  Mathematics  in  the  University  of  Pennsylvania,  Author  of  "A  Treatise  on  Poli- 
tical Economy." 

In  One  large  Octavo  Volume  of  over  Six  Hundred  and  Fifty  double  columned  pages. 

The  numerous  subscribers  who  have  been  waiting  the  completion  of  this  volume  can  now  perfect 
their  sets,  and  all  who  want  a  Register  of  the  Events  of  the  last  Fifteen  Years,  for  the  Whole 
World,  particularly  embracing  interesting  scientific  investigations  and  discoveries,  can  obtain  this 
volume  separately,  price  Two  Dollars  uncut  in  cloth,  or  Two  Dollars  and  Fifty  Cents  in  leather, 
to  match  the  styles  in  which  the  publishers  have  been  selling  sets. 

Subscribers  in  the  large  cities  can  be  supplied  on  application  at  any  of  the  principal  bookstores  ; 
and  persons  residing  in  the  country  can  have  their  sets  matched  by  sending  a  volume  in  charge  of 
friends  visiting  the  city. 

Complete  sets  furnished  at  very  low  prices  in  various  bindings. 

'•The  Conversations  Lexicon  (Encyclopfcdia  Americana)  has  becoiue  a  household  book  in  all  the  intelli- 
gent families  in  America,  and  is  undoubtedly  the  best  depository  of  biographical,  historical,  geogrnphical  and 
political  information  of  that  kind  which  discriminating  readers  require.  There  is  in  the  present  volume  much 
matter  purely  scieutific,  which  was  all  the  niore  acceptable  to  us  that  it  was  unexpected."— <StWtOTa«'«  Journal. 


LEA  &  BLANCHARD'S  PUBLICATIONS. 


FOWNES'  CHEMISTRY  FOR  STUDEJMTS. 

elementary' CHEMISTRY. 

THEORETICAL  AND  PRACTICAL.  ' 

BY  GEORGE  FOWNES,  Ph.  D., 

Chemical  Lecturer  in  the  Middlesex  Hospital  Medical  School,  &c.  &c. 

With  Numerous  Illustrations.    Edited,  with  Additions, 
BY  ROBERT  BRIDGES,  M.  D., 

Professor  ofGeneral  and  Pharmaceutical  Chemistry  in  the  Philadelphia  College  of  Pharmacy,  &c.  &c. 
In  one  large  duodecimo  volume,  sheep  or  extra  cloth. 
Though  this  work  has  been  so  recently  publislied,  it  has  already  been  adopted  as  a  text-book  by  many  of  ihe 
Medical  Institutions  ihrougbotii  the  country.  As  a  work  for  the  first  class  student,  and  as  an  introduction  to 
the  larger  systems  of  Chemistry,  such  as  Graham's,  there  has  been  but  one  opinion  expressed  concernijig  u', 
and  It  may  )iow  be  considered  hs 

THE  TEXT-BOOSL  FOR  THE  CHEMICJiMj  STUDEJTT. 

"  An  admirable  exposition  of  tlie  present  stale  of  chemical  science,  simply  and  clearly  written,  and  display- 
ing a  thorough  praetical  knowledge  of  its  details  as  well  as  a  profound  acquaintance  with  its  principles.  The 
illustrations,  and  the  whole  getting-up  of  the  book,  merit  our  highest  praise."— iJmis/t  and  Foreign  Medical 
Review. 

•'  Remarkable  for  its  clearness,  and  the  most  concise  and  perspicuous  work  of  the  kind  we  have  seen,  admi- 
ral.'ly  calculated  to  prepare  the  student  for  the  more  e]ai)oraie  treatises." — Pharmaceutical  Journal. 

This  work  of  Fownes,  while  not  enlarging  on  ihe  subject  as  much  as  Graham,  is  far  more  lucid  and  expanded, 
than  the  usual  small  introductory  works.  Persons  using  it  may  rely  upon  its  being  kept  up  to  the  day  by  fre- 
quent revisions. 

GRAHAM'S   CHEMISTRY. 

THE  ELEMENTS~OF   CHEMISTRY. 

INCLUDING   THE    APPLICATION   OF   THE   SCIENCE  TO  THE   ARTS. 
"With.  Kumerous  Illixstratlons. 

Br  THOMAS  GRAHAM,  F.  R.  S  L.  and  E.  D., 
Professor  of  Chemistry  in  University  College,  London,  &c.  &c. 

WITH  NOTES  AND  ADDITIONS, 

Br  ROBERT  BRIDGES,  M.  D.,  &c.  &c. 
In  one  volume  octavo. 


SIMON'S    CHEMISTRY   OF    MAN. 

ANIMAL   cllBMISTRir, 

WITH  REFERENCE  TO  THE  PHYSIOLOGY  AND  PATHOLOGY  OF  MAN. 
BY  DR.  J.  FRANZ  SIMON. 

TRANSLATED  AND   EDITED  BY 

GEORGE  E.  DAY,  M.  A.  &  L.  M.  Cantab.,  &c. 
With  plates.    In  one  octavo  volume,  of  over  seven  hundred  pages,  sheep,  or  in  tvjo  parts,  "boards. 

This  important  work  is  now  complete  and  may  be  had  in  one  large  octavo  volume.  Those  who  obtained  the 
first  part  can  procure  the  second  separate. 

•'No  treatise  on  physiological  chemistry  approaches,  in  fulness  and  accuracy  of  detail,  the  work  which 
stands  at  the  head  of  this  article.  It  is  the  production  of  a  man  of  true  German  assiduity,  who  has  added  to  his 
own  researches  the  results  of  the  labors  of  nearly  every  other  inquirer  in  this  interesting  branch  of  science — 
The  death  of  such  a  laborer,  which  is  mentioned  in  the  preface  to  the  work  as  having  occurred  prematurely  in 
1342,  is  indeed  a  calamity  to  science.  He  had  hardly  reaehed  the  middle  term  of  life,  and  yet  had  made  himself 
known  all  over  Europe,  and  in  our  country,  where  his  name  has  been  familiar  for  several  years  as  among  the 
most  successful  of  the  cultivators  of  the  Chemistry  of  Man  ....  It  is  a  vast  repository  of  facts  to  which  the 
teacher  and  student  may  refer  with  equal  satisfaction. "—J'/k  Western  Journal  of  Medicine  and  Surgery. 

"  The  merits  of  the  work  are  so  universally  known  and  acknowledged,  as  to  need  no  further  commendation 
at  our  hands." — iV.  Y.  Journal  of  Medicine  and  Svrge/ry 


THE  CHEMISTRY  OF  THE  FOIIR  SEASONS— A  NEW  WORK. 
THE  CHEMISTRY  OF  THE  FOUR  SEASONS, 

SPRING,  SUMMER,  AUTUMN  AND  WINTER. 

AN   ESSAY    PRINCIPALLY   CONCERNING    NATURAL    PHENOMENA    ADMITTING    OF 

ILLUSTRATION  BY  CHEMICAL  SCIENCE.  AND  ILLUSTRATING  PASSAGES 

OF  SCRIPTURE. 

BY  THOMAS  GRIFFITHS, 

Professor  of  Chemistry  in  the  Medical  College  of  St.  Bartholomew's  Hospital,  &c. 
In  One  very  neat  Volume.,  royal  1 2mo.,  of  Four  Hundred  and  Fifty  large  Pages,  extra  cloth,  illus- 
trated with  numerous  Wood-cuts. 
"  VVe  would  especially  recommend  it  to  youths  commencing  the  study  of  medicine,  both  as  an  incentive  to 
their  natural  curiosity  and  an  imroduction  to  several  of  those  branches  of  science  which  will  necessarily  soon 
occupy  their  attention      We  would  notice  further,  and  with  commendation,  that  a  sound  and  rational  natural 
theology  is  spread  through  the  whole  work.^^— The  British  and  Foreign  Medical  Revieto. 

"This  interesting  and  attractive  volume  is  designed  to  illustrate  by  easy  and  familiar  experiments,  and  in 
popular  language,  many  of  the  phenomena  going  on  in  the  realm  of  nature  through  the  ever-varying  year,  and 
to  exemplify  and  explain  many  beautiful  scriptural  allusions  involving  the  play  of  chemical  and  philosophical 
laws.  Nor  has  the  gifted  author  failed  in  accomplishing  his  laudable  purpose.  His  agreeable  style,  the  eor- 
reciuess  of  his  philosophical  views,  and  especially  ttxe  high  moral  and  religious  bearing  of  his  work,  cannot 
but  secure  for  him  the  comnnendaiion  and  patronage  of  the  intelligent  and  virtuous."— SowiAern  Medical  and 
Sur  gical  Journal. 


C5  .  LEA  &  BLANCHARD'S  PUBLICATIONS.  - 

LECTURES  ON  THE  OPERATIONS  OF  SURGERY, 

AND  ON  ' 

DISEASES  AND  ACCIDENTS  REQUIRING  OPERATIONS, 

DELIVERED   AT   UNIVERSITY    COLLEGE,    LONDON. 
BY  ROBERT  LTSTON,  Esq.,  F.  R.  S.,  &c. 

EBITEB,     WITH     NUMEROUS     ALTEKATIONS     AND     ADDITIONS, 

BY  T.  D.  MUTTER,  M.D., 

Professor  of  Surgery  in  the  JefTerson  Medical  College,  Philadelphia. 

In  One  I^arge  and  Beautifully  Printed  Octavo  Volume. 

WITH  TWO  HUNDRED  AND  SIXTEEN  ILLUSTRATIONS  ON  WOOD. 

More  than  one-third  of  this  volume  is  by  Professor  Miitter,  embodying  elaborate  treatises  on 
Plastic  Operations,  Staphyloraphy,  Club-Foot,  Diseases  of  the  Eye,  Deformities  from  Burns,  &c.&c. 


iL  SYSTEM  OP  PRAOTiaAL  STTR^ERY. 

BY  WILLIAM  FERGUSSON,  F.  R.  S.  E. 

SECOND   AMERICAN   EDITION,   REVISED   AND  IMPROVED. 

With  Tw^  Hundred  and  Fifty-two  Illustrations  from  Drawings  by  Bagg,  Engraved  by  Gilbert  f 

With  Notes  and  Additional  Illustrations, 

BY    GEORGE    W.    NORRIS,M.    D.,  &c. 

In  one  beautiful  octavo  volume  of  six  hundred  and  forty  large  pages. 


THE  PRINCIPLES  AND  PRACTICE  OF 

OBSTETRIC  MEDICINE  AND  SDRGERY, 

IN  REFERENCE  TO  TKE  PROCESS  OF  PARTURITION. 

ILLUSTRATED  BT 

Oi»«  hundred  and  forty-eight  Jjarg-e  JPiffures  on  55  JLithoffraphic  JPlate$, 

BY  FRANCIS  H.  RAMSBOTHAM,  M.  D.,  &c. 

A  NEW  EDITION,  FROM  THE  ENLARGED  AND  REVISED  LONDON  EDITION. 

In  one  large  imperial  octavo  volume,  well  bound. 

Philadelphia,  August  6th,  1845. 
Messrs.  Lea  &  Bla.nchard. 

Gentlemen  :— I  have  looked  over  the  proofs  of  Ramsbotham  on  Human  Parturition,  with  its  important  im- 
provements, from  the  new  London  edition. 

This  Work  needs  no  commendation  from  me,  receiving,  as  it  does,  the  unanimous  recommendation  of  the 
British  periodical  press,  as  the  standard  work  on  Midwifery;  "chaste  in  language,  classical  in  composition, 
happy  in  point  of  arrangement,  and  abounding  in  most  interestmg  illustrations." 

To  the  American  public,  therefore,  it  is  most  valuable— from  its  mtrinsic  undoubted  excellence,  and  as  being 
the  best  authorized  exponent  of  British  Midwifery.  Its  circulation  will,  I  trust,  be  extensive  throughout  our 
country. 

There  is,  however,  a  portion  of  Obstetric  Science  to  which  sufficient  attention,  it  appears  to  me,  has  not  been 
paid.  Through  you,  I  have  promised  to  the  public  a  work  on  this  subject,  and  although  the  continued  occupa- 
tion of  my  lime  and  thoughts  in  the  duties  of  a  teacher  and  practitioner  have  as  yet  prevented  ihe  fulfilment  of 
the  promise,  the  day,  I  trust,  is  not  distant,  when,  under  the  hope  of  being  useful,  I  shall  prepare  an  account  of 
the  Mechanism  of  Labor,  illustrated  by  suitable  engravings,  which  may  be  regarded  as  an  addendum  to  the 
fitandard  works  of  Ramsbotham,  and  our  own  Dewees. 

Very  respectfully,  yours, 

HUGH  L.  HODGE,  M.D., 
Professor  of  Obstetrics,  S(C.  SfC,  in.  the  Unuxrsity  of  Pennsylvania, 


PROFESSOR  CHAPMAN'S'!WORKS  ON  PRACTICE. 

A  COMPENDIUM  OF  LECTURES  ON  THE 

THEORY   AND    PRACTICE  OF    MEDICINE. 

DELIVERED   BY  PROFESSOR  CHAPMAN  IN  THE  UNIVERSITY  OF  PENNSYL- 
VANIA.   PREPARED,  WITH   PERMISSION,  FROM  DR  CHAPMAN'S  MA- 
NUSCRIPTS, AND  PUBLISHED  WITH  HIS  APPROBATION, 
By  N.  D.  BKNKDICT,  M.  D.    In  one  very  neat  octavo  volume. 

f^  This  work  contains  the  diseases  not  treated  of  in  the  two  following. 


LECTURE3  ON  THE  MORE  IMPORTANT  DISEASES  OF  THE 

THORACIC  AND  ABDOMINAL  VISCERA. 

Delivered  in  the  University  of  Pennsylvania,  by  N.  Chapmabt,  M.  D.,  Professor  of  the  Theory 
and  Practice  of  Medicine,  &c.    In  one  volume,  octavo. 


LECTURES  ON  THE  MORE  IMPORTANT 

ERUPTIVE  FEVERS,  HEMORRHAGES  AND  DROPSIES, 

AND  ON  GOUT  AND  RHEUMATISM, 

Delivered  in  the  University  of  Pennsylvania  by  N.  Chapmax,  M.  D.,  Professor  of  the  Theory 
and  Practice  of  Medicine,  &c.  &c.    In  one  neat  octavo  volume. 


LEA  &  BLANCHARD'S  PUBLICATIONS.  27 

A  NEW  MEDICAL  DICTIONARY. 

In  one  Volume,  large  12mo.,  now  ready,  at  a  low  price. 


A  DICTIONARY  OF 

THE    TERMS    USED    IN    MEDICINE 

AND 

THE    COLLATERAL    SCIENCES; 
BY  RICHARD  D.  HOBLYN,  A.  M.,  Oxon. 

FIRST    AMERICAN,    FROM    THE    SECOND    LONDON    EDITION. 

REVISED,  WITH  NUMEROUS  ADDITIONS, 

BY  ISAAC  HAYS,  M    D., 

Editor  of  the  American  Journal  of  the  Medical  Sciences. 

A  NEW  AN^^COMPLEtFw^     ON  FEVERS. 

FEVERS; 

THEIR  DIAGNOSIS,  PATHOLOGY  AND  TREATMENT. 

PREPARED  AND  EDITED  WITH  LARGE  ADDITIONS, 

FROM  THE  ESSAYS  ON  FEVER  IN 

TWEEDIE'S  LIBRARY  OF  PRACTICAL  MEDICINE, 
BY  MEREDITH  CLYMER,  M.  D., 

Professor  of  the  Principles  and  Practice  of  Medicine  in  Franklin  Medical  College,  Philadelphia  / 

Consulting  Physician  to  the  Philadelphia  Hospital ;  Fellow  of  the  College  of  Physicians^  SfC.  ^c. 

In  one  octavo  volume  of  600  pa  ges. 

THE  SURGICAL  WORKS  OF  SIR  ASTLEY  COOPER. 

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B^    SIK  ASTLEY  COOPER,  BART. 

Edited  by  C.  ASTON  KEY,  Surgeon  to  Guy's  Hospital,  &c. 
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ON  THE  STRUCTURE  AND  DISEASES  OF  THE  TESTIS. 

Illustrated  by  120  Figures.     From  the  Second  London  Edition. 
BY  BRANSBY  B.  COOPER,  Esq. 

AND  ALSO  ON  THE  AIN ATOMY  OF  THE  THYMUS  GLAND. 

Illustrated  hy  fifty-seven  Figures. 
The  two  works  together  la  one  beautiful  imperial  octavo  volume,  illustrated  with  twenty-nine  plates. 

ANATOMY  AND   DISEASES   OF   THE   BREAST,  &c. 

THIS  LARGE  AND  BEAUTIFUL  VOLUME  CONTAINS  THE   ANATOMY  OF  THE  BREAST 
THE    COMPARATIVE    ANATOMY    OF   THE    MAMMARY    GLANDS;    ILLUSTRA- 
TIONS OF  THE  DISEASES  OF  THE  BREAST  ; 

And  Twenty-five  Miscellaneous  Surgical  Papers,  now  first  published  in  a  collected  form. 

BY  SIR  ASTLEY  COOPER,  Bakt.,  F.  R.  S.,  &c. 

The  whole  m  one  large  imperial  octavo  volume,  illustrated  with  two  hundred  and  fifty-two  figures. 

A  TREATISE  ON  DISLOCATIONS  AND  FRACTURES  OF  THE  JOINTS. 

By  Sir  ASTLEY  COOPER,  Bart.,  F.  R.  S.,  Sergeant  Surgeon  to  the  King,  &c. 

A  New  Edition  much  enlarged  ; 

Edited  by  BRANSBY  COOPER,  F.  R.  S.,  Surgeon  to  Guy's  Hospital. 

With  additional  observations  from  Professor  JOHN  C.  WARREN,  of  Boston. 

With  numerous  Engravings  on  Wood,  after  designs  by  Bagg,  a  Memoir  and  a  splendid  Portrait  of  Sir  Astley 

In  one  octavo  volume. 


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LEA   &  BLANCHARD'S  PUBLICATIONS.  29 

the  Diseases  of  the  Heart  and  Lungs.  By  H.  M.  Hughes,  M.  D.,  &c.  fn  one  12mo. 
volume,  with  a  plate. 

INTRODUCTION  TO  PRACTICAL  ORGANIC  CHEMISTRY;  based  on  the  Works  of 
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numerous  Cuts. 


30  LEA  &  BLANCHARD'S  PUBLICATIONS. 

A  TREATISE  ON  THE  DISEASES  OF  FEMALES,  ~ 

AND  ON  THE  SPECIAL  HYGIENE  OF  THEIR  SEX. 

WITH  NUMEROUS  WOOD-CUTS. 

BY     COLOMBAT     DE     L'ISERE,M.D., 

Chevalier  of  the  Legion  of  Honor  ;  late  Surgeon  to  the  Hospital  of  the  Rue  de  Valois,  devoted  to  the 

Diseases  of  Females,  SfC.  SfC. 

TRANSLATED,  WITH  MANY  NOTES  AND  ADDITIONS, 

BY  C.  D.  METGS,  M.  D., 

Frofessor  of  Obstetrics  and  Diseases  of  Women  and  Children  in  the  Jefferson  Medical  College,  ^c.  ^e. 

In  one  large  volume,  8vo. 

iroii.MTT  ojy  THE  noa. 

T  H  E  ~D  O  G . 

BY  WILLIAM  YOUATT. 

WITH  NUMEROUS  AND  BEAUTIFUL  ILLUSTRATIONS. 

EDIIED  BY  E.  J.  LEWIS,  M.  D.,  &c.  &c. 

tn  One  heaulifully printed  Volume,  Crown  Octavo,  with  Twenty. four  Plates,  done  up  in  richcrim- 

son  extra  cloth. 
"  With  this  explanation  of  his  connection  with  the  work  he  leaves  it,  in  the  hope  that  it  may 
prove  of  value  to  the  sportsman  from  its  immediate  relation  to  his  stirring  pursuits;  to  the  general 
reader  from  the  large  amount  of  curious  information  collected  in  its  pages;  and  to  the  MEDICAL 
STUDENT  from  the  light  it  sheds  on  the  PATHOLOGY  AND  DISEASES  of  the  dog,  by  which  he 
will  be  surprised  to  learn  how  many  ills  that  animal  shares  in  common  with  the  human  race." — 
Editor's  Pkeface. 


LANDRETH'S  JOHNSON'S_GARDENERS'  DICTIONARY. 

JXT3T  RBADT. 

A  DICTIONARY  OF  MODERN  GARDENING. 

BY  GEORGE  WILLIAM  JOHNSON,  Esa., 

Fellow  of  the  Horticultural  Society  of  India,  &c.  &c. 

With    One    Hundred   and    Eighty   Wood-Cuts. 

EDITED,  WITH  NUMEROUS  ADDITIONS, 

BY  DAVID  LANDRETH,  of  Philabelphia. 

Tn  the  American  edition,  many  modifications  and  additions  have  been  made,  so  as  to  render  the  work  a  com- 
plete and  satisfactory  book  of  reference  upon  every  subject  connected  with  modern  gardening  in  its  most  ex- 
tended sense;  while  great  care  has  been  exercised  in  adapting  it  to  the  practice  of  every  section  of  this  country. 

Numerous  wood-cut  illustrations  have  been  added,  and  the  publishers  present  a  beautiful  volume  of  near 
650  pages,  in  a  clear  but  small  type,  well  done  up  in  extra  cloth,  and  at  a  very  low  price.  Such  a  work  has 
long  been  needed  by  the  many  persons  who  cannot  afford  to  purchase  the  large  expensive  work  of  Loudon. 

Sold  by  all  Booksellers,  JYurserymen  and  Seedsmen  in  the  United  States, 
CONTENTS    OF    THE 

AMEBtCAN  JOURNAL  OF  THE  I^EDICAL  SCIENCES, 

For  .Spril,  1847. 

Memoirs  and  Cases — Art.  I.  History  of  seven  cases  of  Pseudo-membranous  Laryngitis,  or  True  Croup. 
By  J.  F.  Meigs,  M.  D.  II.  Poisonous  Properties  of  the  Sulphate  of  Quinine.  By  Wm.  O.  Baldwin,  M.  D.  III. 
Removal  of  the  Superior  Maxilla  for  a  tumour  of  the  antrum;  Apparent  cure.  Retuinof  the  disease.  Second 
operation.  Sequel.  By  J.  Marion  Sims,  M.  D.  [With  a  wood-cut]  IV.  Lacerationofthe  Perineum.  By  John 
V.  Mettauer,  M.  D.  V.  Report  of  Cases  treated  in  Cincinnati  Commercial  Hospital.  By  .lohn  P.  Harrison, 
M.  D.  VI.  Surgical  Cases.  By  Geo.  C.  Blackman,  M.  D.  [With  a  wood-cut.]  VII.  Cases  of  Paralysis 
peculiar  to  the  Insane.  By  Pliny  Earle,  M.  D.  VIH.  Contributions  to  Pathology;  being  a  Report  of  Fatal 
Cases  taken  from  the  records  of  the  U.  S.  Naval  Hospital,  New  York.  By  W.  S.  W.  Ruschenberger,  M.  D. 
IX.  Caseof  Hydrops  Pericardii  suddenly  formed,  with  Remarks.  By  S.  Jackson,  M.  D.  X.  Case  of  Tuber- 
cles in  the  pericardium,  vena  cava,  columnse  carnese,  pleura,  lungs,  liver,  &c.,  with  Meningitis.  By  J.  D. 
Trask,  M.  D.  XL  On  letting  Blood  from  the  Jugular  in  the  Diseases  of  Children.  By  Charles  C.  Hildreth, 
M.D. 

Review. — XIT.  Lectures  on  Subjects  connected  with  Clinical  Medicine ;  comprising  Diseases  of  the 
Heart.    By  P.  M.  Latham,  M.  D. 

Bibliographical  Notices.— -XIII.  Green  on  Diseases  of  the  Air  Passages.  XIV.  Condie  on  the  Diseases  of 
Children.  Second  edition.  XV.  Royle's  Materia  Medica  and  Therapeutics.  Edited  by  Carson.  XVI.  VogePs 
Pathological  Anatomy  of  the  Human  Body.  Translated,  with  additions,  by  George  E.  Day.  XVII.  Trans- 
actions of  the  College  of  Physicians  of  Philadelphia.  From  September  to  November,  1646,  inclusive. 
XVIII.  Wharton  Jones  on  the  Principles  and  Practice  of  Ophthalmic  Medicine  and  Surgery.  Edited  by 
Isaac  Hays,  M.  D.  XIX.  Wood  on  the  Practice  of  Medicine.  XX.  Wernher's  Manual  of  General  and 
Special  Surgery.  XXI.  Baumgarten's  Surgical  Almanac  for  the  years  lc44  and  1845.  XXII.  Wilson's 
System  of  Human  Anatomy,  General  and  Special.  Third  American  from  the  third  London  edition.  Edited 
by  Paul  B  Goddard,  M.  D.  XXHI.  Von  Behr's  Handbook  of  Human  Anatomy,  General,  Special  and 
Topographical.    Translated  by  John  Birkelt. 


LEA  &  BLANCH ARD'S  PUBLICATIONS.  31 

Contents  of  the  Medical  Journal  Continued. 

QUARTERLY    RETROSPECT, 

A  SUMMARY  OF  THE  IMPROVEMENTS  AND  DISCOVERIES  IN  THE  MEDICAL  SCIENCES. 

Foreign  Intelligence— Anatomy  AND  Physiology— 1.  QMfA;e«  on  Intimate  Structure  of  Bone.  2.  Meckel 
on  Processor  Secretion.  3.  Blondlot  on  the  Propertiesof  the  Bile.  4.  .Bam?>rrg-§-e  on  Supplementary  Spleen, 
death  from  the  patient  being  placed  in  the  supine  position.  5.  Robinson  on  the  Nature  and  Source  of  the 
contents  of  the  Foetal  Stomach.    6.  Prof.  Bischoff  on  the  Absorption  of  Narcotic  Poisons  by  the  Lymphatics. 

Materia  Medica  and  Pharmacy. — 7.  Battley  on  Syrup  of  Iodide  and  Chloride  of  Iron.  8.  Rlcord  on  Bro- 
mide of  Potassium  as  a  substitute  for  the  Iodide.  9.  VoUlemier  on  Santonine.  10.  GweftoMri  on  the  changes 
of  composition  which  the  Tincture  of  Iodine  undergoes  in  keeping.  11.  Mellon  on  the  Action  of  the  Acetate 
of  Morphia  on  Children. 

Medical  Pathology  and  Therapeutics  and  Practical  Medicine. — 12.  Bennett  on  Anormal  Nutrition 
and  Diseases  of  the  Blood.  13.  Rostan  on  Acute  Spinal  Myelitis.  14.  Rostan  on  Curability  of  Hypertrophy 
of  the  Heart.  15.  Crisp  on  Rupture  of  the  left  Ventricle  of  the  Heart.  16.  Francis  on  Aneurism  of  the  Basi- 
lar Artery.  17.  Lombard^s  Observations  on  Sudden  deaths,  probably  dependent  on  Diseases  of  the  Heart 
and  large  Blood-vessels.  18.  Carson  on  Obliteration  of  the  Vena  Cava  Descendens.  19.  Thompson  on 
Treatment  of  Chronic  Bronchitis  and  Bronchial  Asthma.  20.  Muklbauerh  Microscopic  Researches  on  the 
Absorption  of  Pus.  21.  Briquet  on  Mercurial  Ointment  in  Variola.  22.  Bell  on  Rupture  of  Lateral  Sinus  of 
Dura  Mater.  23.  Watts  on  Tubercles  in  Bones.  24.  Gendrin  on  Hysterical  Affections.  25.  Cottereau's 
Remedy  for  Toothache.  26.  Prof  Trousseau  on  Anatomy  of  Pneumonia  in  Infants.  27.  Volz  on  Hooping 
Cough  an  Exanthemata.  28.  Crisp  on  Infantile  Pleurisy.  29.  Yowi  on  Abscess  of  the  Brain  in  a  Child.  30. 
Trousseau  on  the  Employment  of  Nux  Vomica  in  the  Treatment  of  St.  Vitus'  Dance. 

Surgical  Pathology  and  Therapeutics  and  Operative  Surgery.— 3L  Prof.  Syme  on  Amputation  at 
the  Shoulder  Joint  for  Axillary  Aneurism.  32.  Whipple  on  Amputation  at  the  Hip  Joint.  3-3.  Prof.  Ehr- 
mann on  Successful  Extirpation  of  a  Polypous  Tumour  of  the  Larynx.  34.  Bellingham  on  Compression  in 
Aneurism.  35.  Orr^s  Case  of  Tracheotomy.  36.  Holmes  Coote  on  Cancer  of  the  Breast  in  the  Male.  .37. 
Moore  on  Gunshot  wound  of  the  Lung,  where  the  ball  lodged  fifty  years.  33.  On  the  Employment  of  Iodide 
of  Potassium  in  the  Treatment  of  Syphilis.  39.  Application  of  ice  in  the  treatment  of  injuries.  40.  Lenoiroa 
Ununited  Fracture  successfully  treated  by  Acupuncturation.  41.  Prof.  Syme  on  Amputation  of  the  Thigh. 
42.  Curling'^s  Case  of  Fatal  Internal  Strangulation  caused  by  a  cord  prolonged  from  a  Diverticulum  of  the 
Ileum.  43.  Golding  Bird  and  John  Hilton  on  Case  of  Internal  Strangulation  of  Intestine  relieved  by  Opera- 
tion. 44.  Fergussonon  Strangulated  Congenital  Hernia  in  an  infant  seventeen  days  old,  requirinp^  opera- 
tion. 45.  Guersant,  Jr.,  on  Surgical  Treatment  of  Croup.  46.  Geoghegan  on  Partial  Amputation  of  the  Foot. 
47.  Report  of  a  Committee  of  the  Surgical  Society  of  Ireland,  relative  to  the  use  and  effects  of  Sulphuric 
Ether. 

Ophthalmology.— 48.  Prof.  Jacob  on  Foreign  Bodies  in  the  Eye.  49.  Dixon''s  Remarkable  Case  of  Injury 
of  the  Eye.  50.  Szokalskion  Obscurations  of  the  Cornea  in  their  Histological  relations  with  reference  to  the 
Practice  of  Ophthalmic  Surgery.    51.  Berncastle  on  Amauro  sis  from  Hydatid  Cyst  in  the  Brain. 

Midwifery.— 52.  Robiquet  on  Remarkable  case  of  spontaneous  rupture  of  the  Uterus  during  labour— Re- 
covery. 53.  Le  Chaptois^  Case  of  Vaginal  Entero-hysterocele  reduced  by  taxis,  and  maintamed  in  place 
by  the  introduction  of  sponges  in  the  v  agina.  54.  K-iihne  on  Rupture  of  the  Uterus— abdominal  section — 
recovery.  55.  Czajewski  on  AVound  of  the  Gravid  Uterus — premature  delivery — peritonitis— recovery.  56. 
Bennett  on  Inflammatory  Ulceration  of  the  Cervix  Uteri  during  Pregnancy,  and  on  its  Influence  as  a  Cause 
of  Abortion.  67.  Caesarian  Operation  performed  by  Mr.  Skey,  at  St.  Bartholomew's  Hospital,  the  patient 
being  rendered  insensible  by  ether.  58.  Pochhammer  on  Congenital  protrusion  of  the  Liver  through  the 
umbilical  ring.  59.  Caesarian  Section.  60.  iSowz  on  Lacerated  Perineum.  61.  DepowZ  on  Asphyxia  neona- 
torum.   62.  Klencke  on  Diet  in  Infancy. 

Medical  Jurisprudence  and  Toxicology.— 63.  Taylor  on  Contested  identity  determined  by  the  teeth. 
64.  Blake  on  Poisons.  65.  Delirium  Tremens  in  an  Infant.  66.  Hamilton  on  the  Echites  Suberecta.  67. 
Dupasquier  on  Vapours  of  Phosphorus,  Lucifer  Matches.  68.  Thompson  on  the  mode  of  testing  the  presence 
of  minute  quantities  of  Alcohol.  69.  Invalidity  of  a  Contract  made  by  a  Lunatic.  70.  Procuring  of  Abortion. 
71.  Lepage's  Case  of  Poisoning  by  Arsenic  relieved  by  the  use  of  Magnesia.  72.  Sale  of  Poisonous  Sub- 
stances. 

Medical  Education.— 73.  The  Edinburgh  Statutes  regarding  the  Degree.  74.  Medical  Organization  in 
Spain. 

Foreign  Correspondence.— Letters  to  the  Editor  from  London.  Sulphuric  Ether  in  Surgical  Operations 
at  Vienna. 

American  Intelligence— Original  Communications.— ParJbnan's  Anatomical  Anomaly.  Tyler''s  Ante- 
version  of  the  Womb  with  adhesion  of  Os  Uteri  to  body  of  4th  Lumbar  Vertebra,  &c. 

Domestic  Summary  —Beck  on  Effects  of  Mercury  on  the  Young  Subject.  Brainard  on  Amputation  for 
Scrofulous  Diseases  of  the  Joints.  Baker  on  Case  of  Vicarious  Menstruation  from  an  Ulcer  on  the  right 
Mamma.  Allen  on  Singular  case  of  laceration  of  the  Broad  Ligaments.  McLean  on  Blindness  caused  by 
the  use  of  Sulphate  of  Quinine.  Harrison''s  Speculations  on  the  Cause  of  Yellow  Fever.  Herrick  on  Foreign 
Bodies  in  the  Organs  and  Tissues  of  the  Body.  Srvett  on  Case  of  Empyema  in  which  the  operation  for  Para- 
centesis Thoracis  failed  from  a  cause  not  generally  noticed.  MPheeters  on  Rheumatism,  with  Hypertrophy 
of  both  eyes.  Draper  on  the  Cause  of  the  Circulation  of  the  Blood.  Little  on  Ischuria  Renalis.  Hogan  on 
Strychnine  in  Chorea.  Deaderick  on  Excision  of  the  Inferior  Maxillary  Bone  for  Osteo- Sarcoma.  Cain  on 
Imperforate  Prepuce.  Couper  on  Medical  Schools  of  the  United  States.  Warren  on  Inhalation  of  Ether. 
Burwell  on  Absence  of  one  Kidney.  Brainard  on  Dislocation  of  the  Elbow.  Gilman  on  Presentation  of 
the  shoulder,— prolapsed  Cord,— cord  not  pulsating,  yet  child  born  alive.  National  Medical  Convention. 
Delegates  to  National  Medical  Convention.  Arrangements  for  the  Meeting  of  the  National  Medical  Con- 
vention.   Resignation  of  Professor  Warren.    New  Medical  Books. 

LEA  &  BLANCHARD,  Philadelphia. 
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Elements  of  physiology^ 


4  I  v>  *  '  J 


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